Are gas emissions at Yellowstone dangerous? You may ask this question while walking along the boardwalks of Yellowstone's geyser basins, where you'll see billowing white gas plumes or wrinkle your nose at a stinky "rotten egg" smell. In fact, it's a question that has been considered by scientists and visitors to the area for over a century.

Learn all about the potential hazards of gases at Yellowstone in this week's Yellowstone Caldera Chronicles.

Fans of Yellowstone Caldera Chronicles are likely well aware of the Yellowstone Volcano Observatory (YVO) and its existence as a consortium of different state, federal and university partners (more details are available in a previous YCC article). You might not be so familiar, though, with how YVO fits in with the rest of volcano observatories in the U.S.

For the scoop, check ou this week's issue of Yellowstone Caldera Chronicles!

Does there need to be hot water at the surface for an area within Yellowstone to be an active hydrothermal area? No, there's another clue...unvegetated, bleached, and steaming landscapes. The bleached areas are called acid-sulfate ground. They form when high heat flow and large emissions of acid gases, such as carbon dioxide (CO2) and hydrogen sulfide (H2S), alter the surface rock and create poor growing conditions for most types of plants. Yellowstone's acid-sulfate areas emit much greater quantities of gas than what is emitted from the geyser basins. For scientists who study magmatic gases, these areas are "the place to be" for learning more about the underlying magma system.

If you could travel to Yellowstone 20,000 years ago, what would you see? Erupting geysers? Scenic thermal springs? Herds of bison and elk? No! In fact, you would see an ice sheet that was thousands of feet thick! And the retreat of this ice sheet might have resulted in some of the largest hydrothermal explosions anywhere on Earth in the last several thousand years. Read all about it in this week's Yellowstone Caldera Chronicles!

Yellowstone is one of the most dynamic places on Earth, with active volcanism, seismic swarms, strong earthquakes, episodic ground deformation of up to nearly 20 cm/yr (8 in/yr), and extraordinarily high heat flux that is greater than 40 times the continental average (in places it is up to 2000 times average!). It is this heat that fuels the world's largest hydrothermal system of geysers, fumaroles and hot springs. From last week's Caldera Chronicles article we know that the ultimate source of the heat is a hotspot that transports material to the surface from deep within the Earth, but how does that heat get to the surface to drive the features that have made Yellowstone famous?

Read all about it!

In 1922, Dr. Thomas Jaggar, MIT professor and founder of the Hawaiian Volcano Observatory, took a horse-pack trip through Yellowstone. After the journey, Jaggar stated: "Anyone who has spent summers with pack-train in a place like Yellowstone comes to know the land to be leaping. ... The mountains are falling all the time and by millions of tons. Something underground is shoving them up." How prophetic were Jaggar's interpretations of Yellowstone's dynamic geology and how volcanic hotspots help shape Earth's surface? In fact, Yellowstone has been shaping the western United States for nearly 17 million years.

Would you like to know more?

Yellowstone National Park's Norris Geyser Basin is a hydrothermal basin full of geysers and thermal pools that are constantly changing. Factors like air temperature, amount of snow and rain, depth of the groundwater table, and the influx of magmatic fluids perturb an already dynamic hydrothermal system. The interaction of these factors with the constantly evolving hydrothermal system is a complex scientific puzzle that sometimes goes a little haywire. We call these quasi-annual events "seasonal disturbances," or just "disturbances" for short, and there may be one occurring right now.

Want to know more about these disturbances? Check out the latest issue of Yellowstone Caldera Chronicles! https://volcanoes.usgs.gov/volcanoes/yellowstone/article_home.html.

The Yellowstone Volcano Observatory (YVO) is aptly named – the consortium of 8 organizations collaborates to study and monitor the active geologic processes and hazards of the Yellowstone Plateau. However, that's not all we do. The U.S. Geological Survey Volcano Hazards Program, one of the consortium members, is responsible for monitoring all potentially active volcanoes in the country. It just so happens that a nearly a dozen of these volcanic centers are within the Yellowstone Volcano Observatory's area of responsibility – and only one of them is Yellowstone! So, what are these other YVO volcanoes? Find out in this week's edition of Yellowstone Caldera Chronicles!

There's been a lot of talk about Steamboat Geyser recently, and rightly so—major eruptions over the past several weeks have been occurring with surprising regularity (every 6 to 8 days), and the 8 eruptions in 2018 ended a period of quiet that lasted 3.5 years. Most of the 2018 eruptions occurred at night or during times when the area was closed to visitors. On June 4, however, the geyser put on a show starting at about 9 a.m. And YVO scientists were on site to witness the spectacle. Read our chief seismologist's perspective in this week's Yellowstone Caldera Chronicles

Steamboat Geyser in Norris Geyser Basin has been measured as the World's tallest geyser (70-120 meters; 230-294 feet). The recent series of geyser eruptions emphasize the importance, variability, power, and beauty of Yellowstone's hot springs, geysers, fumaroles, and mudpots. But, where does all that hot water come from and how does it form such different features?

Check out the latest edition of Yellowstone Caldera Chronicles to read the rest of the story!

Today, YVO scientists monitor ground deformation at Yellowstone using GPS and InSAR. Both techniques rely on signals from Earth-orbiting satellites. But how did scientists study deformation in the "old days" (meaning, prior to the 1990s)? The answer isn't rocket science, but it requires a bit of explanation.

Check out the latest edition of Yellowstone Caldera Chronicles to hear the rest of the story!

Steamboat Geyser, in the Norris Geyser Basin, appears to have entered a phase of more frequent water eruptions, much like it did in the 1960s and early 1980s. Although these eruptions do not have any implications for future volcanic activity at Yellowstone (after all, geysers are supposed to erupt, and most are erratic, like Steamboat), they are nonetheless spectacular, and hopefully many people will have a chance to see Steamboat in eruption during the summer of 2018.

To keep track of the geysering, we will keep an updated count of Steamboat water eruptions on this page. So far in 2018, Steamboat has erupted 13 times (all times below are local):

• March 15, 5:37 AM
• April 19, 4:30 PM
• April 27, 6:30 AM
• May 4, 11:50 PM
• May 13, 3:54 AM
• May 19, 9:49 PM
• May 27, 7:33 PM
• June 4, 9:05 AM
• June 11, 1:06 AM
• June 15, 4:55 PM
• July 6, 1:38 PM
• July 20, 10:36 PM
• August 4, 2:10 PM

Would you like to become a Steamboat watcher? If so, there are three datasets to keep an eye on:

1. Seismic station YNM, in the Norris museum, is the first indicator of an eruption. The webicorder for the station is located here. Look for a thick seismic trace that lasts 30-60 minutes.
2. About 90 minutes after eruption, increased discharge can often be seen at the Tantalus stream gage. You can get that information here. Scroll down to the plot "Discharge, cubic feet per second" and look for a spike and subsequent decay, but be careful...precipitation can cause spikes too! Rainfall information is given in another plot on that page.
3. Each night, temperature data from a sensor in the Steamboat drainage channel is downloaded and posted on line. A sudden and short-lived (minutes-long) spike in temperature indicates a Steamboat eruption. To view those data, go to the YVO monitoring map and zoom in on the Norris area. Hover over any of the thermometer symbols to see their names, and click on the one labeled "Steamboat" to see data from various time periods past.

Have fun! You might also check out the Steamboat page at geysertimes.org for information about Steamboat activity.

Steamboat geyser, in Norris Geyser Basin within Yellowstone National Park, is world famous for being the tallest active geyser in the world. It doesn't erupt that often, sometimes going decades between activity. When Steamboat does erupt, however, the water column can reach 300 feet in the air! And already in 2018, Steamboat has experienced three eruptions, although they have been relatively small compared to previous events.

Read all about the recent activity in this week's Yellowstone Caldera Chronicles!

"Geohydrobiology" sounds like a made-up word—as if the prefixes from multiple scientific fields were strung together to score big points in a game of Scrabble. But it makes more sense when you break it down: geo, meaning Earth; hydro, meaning water; and bio, meaning life. It is easy to understand why studying geohydrobiology is an important endeavor at Yellowstone, a place where Earth, water, and life intersect in unusual and stunning ways.

Read more about how Earth, water, and life come together in this week's edition of Yellowstone Caldera Chronicles!

Yellowstone is a geological wonderland, home to geysers, hot springs, and stunning landscapes, and subject to dynamic forces that result in near constant earthquake activity and ground deformation. But what is driving this activity? What is the source of Yellowstone's heat? New research suggests that Yellowstone's heat engine originates deep within the Earth.

Read all about it in this week's edition of Yellowstone Caldera Chronicles!

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Mike Gottlieb, Project Manager for borehole strainmeter operations with UNAVCO, Inc., in Boulder, CO.

Readers of this column will recall that the Yellowstone Volcano Observatory (YVO) is actually a consortium of agencies that work together to monitor activity at Yellowstone. Today we will take a deeper look at the role that UNAVCO plays in that consortium, and some of the work that we do in the park.

Who is UNAVCO, you may ask? We are a federally funded non-profit charged by the National Science Foundation with operating the National Earth Science Geodetic Facility. We help study the Earth's shape, gravity field, and rotation, using high precision field measurements to quantify small changes in the Earth's surface. Among other things, we built and now operate the Plate Boundary Observatory (PBO), a network of high-precision, geodetic remote monitoring stations that spans the continental US and Alaska.

Within Yellowstone National Park, UNAVCO operates 14 continuous Global Positioning System (GPS) stations, five borehole strainmeter, tiltmeter, and seismic stations, as well as a lake level monitoring system on Yellowstone Lake. These stations are collecting and transmitting data in near real-time, allowing scientists around the world to study small changes (deformation) in the volcano, hydrothermal system, and Lake Yellowstone.

Keeping all this remote equipment running in environments like Yellowstone can be challenging. Engineers from UNAVCO typically visit the park four or five times a year to maintain and upgrade the instruments and associated equipment. Field work ranges from repairing solar panels and enclosures damaged by snow, to upgrading GPS receivers and antennas allow them to track new satellite signals. Getting the data back can be difficult too, as many of these stations are very far from civilization! We employ a combination of cellular, satellite, and local radio networks to carry the information back for archival and analysis.

While most of the fieldwork is scheduled for the summer season, sometimes equipment fails in the winter too. And since Yellowstone is closed to cars from November through April, getting to the remote stations is not trivial. Some years it can involve snowmobiling 60 miles each way at temperatures as low as -20 degrees F, or cross-country skiing several miles from the road. Even finding the equipment can be a challenge as it is often buried under feet of snow.

This past February, a team from UNAVCO visited several sites in the park to repair an offline continuous GPS station and tiltmeter. The work required a 1950s-era Bombardier snow coach and some cross-country skiing to be able to replace the failed communications equipment.

The net result of all this effort is a stream of high-precision and real-time data on how the surface of the Yellowstone region is deforming—critical monitoring data for the Yellowstone Volcano Observatory. The latest measurements indicate that, since 2015, the caldera is subsiding at a rate of a few centimeters (about an inch) per year. The Norris area, in contrast, is uplifting at about the same rate.

All of the data collected by UNAVCO are available to the public, so we encourage you to check out these resources:

• GPS data from the 14 stations in Yellowstone National Park can be accessed from the UNAVCO map interface (just navigate to the Yellowstone region)
• borehole strain data from stations B205, B206, B207, B208, B944, and B950 are available from the strainmeter data archive
• borehole seismic data from stations B205, B206, B207, and B208 are available from the seismic data archive
• borehole tilt data from stations B205, B206, B207, B208, B944, B945, and B950 are available from the tilt data archive

As you explore these datasets, keep in mind the engineers at UNAVCO whose hard work regardless of seasons and conditions keeps the data flowing and ensures that scientists and the public have the information they need to understand surface deformation at Yellowstone.

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Lisa Morgan, emeritus research geologist with the U.S. Geological Survey.

Yellowstone Lake is huge. It is the largest high-altitude (above 2130 m, or 7000 ft) freshwater lake in North America, covering about 341 square kilometers (about 130 square miles). That's about 100 times the size of New York City's Central Park! Over the past decade or so, researchers have discovered many new features on the lake bottom, including a vigorous hydrothermal system that would make for an impressive geyser basin if it were on land. In fact, the hottest hydrothermal vent temperatures measured anywhere in the Park were on the lake bottom—170°C (340°F)! What else might the lake be hiding beneath its surface?

Hot springs, geysers, and fumaroles in and around Yellowstone Lake serve as constant reminders of the volcanically and seismically active Yellowstone Caldera below. The numerous active hydrothermal vents on the floor of Yellowstone Lake are a significant part of the world's largest continental hydrothermal system—there are over 10,000 documented active thermal features in Yellowstone National Park. The region is also one of the most seismically active areas in the intermountain west, has greater than typical heat flow values, and has high rates of precipitation due to its relatively high elevation. Understanding the cause-and-effect relationships between environmental conditions and activity, as well as annual changes in lake level, can yield valuable insights into subsurface processes that are otherwise difficult to observe.

A research team has embarked on a multi-year project to understand how the Yellowstone Lake hydrothermal system responds to geological and environmental forcing. The Hydrothermal Dynamics of Yellowstone Lake (HD-YLAKE) project has major funding and logistical support from the National Science Foundation, the Yellowstone Volcano Observatory, the U.S. Geological Survey, and the National Park Service. The main goals of the project are to understand the relationship between the long-term history of hydrothermal activity in Yellowstone Lake and its influence on aquatic ecosystems and climate-driven processes in the lake and its watershed.

The team is using a two-pronged approach to address these goals. First, they are conducting geophysical and geochemical monitoring of the active system to assess changes over time. Second, they are collecting and analyzing sediment core samples from the lake bottom to study the postglacial (<15,000 year) geologic and climatic history of Yellowstone Lake. This work involves using a research vessel, the RV Annie, as well as a remotely operated vehicle, named Yogi, to study the lake bottom and collect samples.

Over the past few years, the research team deployed a network of pressure–temperature gauges, heat flow equipment, and seismometers on the lake floor. The most intensive work began in the summer of 2017, when they deployed a full-scale network of monitoring instrumentation, including 10 lake-bottom seismometers and two chemical sensors. Equipment will be recovered in August 2018, after which time data analysis can begin.

In addition, the team collected sediment gravity cores from the top 1 m (3 ft) of the lake bed, sediment piston cores that extended as much as 12.1 m (~40 ft) into the lake bed, gastight samples of hydrothermal fluid from thermal vents, and samples of microbial material.

Preliminary examination of the piston and gravity cores reveals that many contain multiple hydrothermal explosion deposits, suggesting a history of repeated small explosions from the Yellowstone Lake area (this confirms previous study of on-land deposits). Analyses are currently under way to determine mineralogy and composition of the sediment. Geochemical analyses of samples of fluid from within the cores will provide information about the composition of hydrothermal waters that exist below the lake floor and will the extent of the lake-bottom hydrothermal vent fields. Finally, studying single-celled organisms, pollen, charcoal, and tephra preserved in the cores will link the aquatic response of the lake to past climate, hydrothermal, and geologic activity.

More information about the HD-YLAKE project can be found here . Stay tuned to Yellowstone Caldera Chronicles for more information on research results as analyses are completed and equipment is recovered in 2018!

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Christina George, outreach and publications manager at the Wyoming State Geological Survey.

By now, readers of Yellowstone Caldera Chronicles know that the Yellowstone Volcano Observatory (YVO) is a consortium of 8 different agencies. Each agency has different priorities and skills, and working together and applying their specialties can bring a better understanding of how Yellowstone works. Today, we'll learn more about the Wyoming State Geological Survey (WSGS) and its role in monitoring and researching Yellowstone's geology.

The WSGS joined the Yellowstone Volcano Observatory (YVO) in 2013 as part of the state agency's efforts to inform and protect residents and visitors from geologic hazards, many of which can originate from the Yellowstone National Park region.

Although established 85 years ago, the roots of the WSGS stretch back to 1877, when Wyoming was still a territory. Over the decades, the agency has been renamed and reorganized several times, but the primary mission has remained essentially the same: to gather, interpret, and disseminate reliable information on state geology.

Thirteen geologists are on staff at the WSGS, which is located on the University of Wyoming campus in Laramie. They conduct studies in the areas of hazards, groundwater, fossils, minerals, coal, and oil and gas. There are also eight support staff, ranging from administration to GIS and outreach. Under the leadership of the Wyoming State Geologist and WSGS Director, Dr. Erin Campbell, the WSGS staff strives to promote the beneficial and environmentally sound use of the state's vast geologic, mineral, and energy resources, while helping protect the public from geologic hazards.

A current example of hazards work is the role of WSGS geologists in multi-agency teams that are tasked with monitoring and investigating two active landslides near Dubois and Alpine, Wyoming. Also, in 2017 the WSGS worked with the U.S. Geological Survey and others to excavate a trench across a scarp on the Teton Fault in northwestern Wyoming. The purpose of the project was to investigate the fault rupture extent and recurrence of past large earthquakes.

Geologic hazards studies by WSGS geologists are particularly important because they are critical for the safety of residents and visitors as well as for providing information to protect property and infrastructure. Geologic hazards that occur across Wyoming's nearly 100,000 square miles include earthquakes, landslides, and volcanic eruptions. More information about geologic hazards in Wyoming can be found on the WSGS website: http://www.wsgs.wyo.gov/hazards/hazards. A region where many of these hazards can and do occur is the Yellowstone National Park area.

The WSGS, through its communications and public outreach program, provides key hazards-based information to Wyoming citizens as well as to the global community. The Yellowstone region is one of Wyoming's precious gems, but it is abundant with geologic hazards, incuding volcanic, hydrothermal, and seismic hazards. The partnership between the WSGS and the YVO serves as an important source of information for state leaders, emergency responders, and the public should a critical situation arise.

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Robert Smith, Distinguished Research Professor with the University of Utah and a founding member of the YVO consortium.

This week, Yellowstone Caldera Chronicles would like to acknowledge one of the unsung heroes of the long-term effort to monitor activity in the Yellowstone region. Dave Drobeck spent nearly three decades building and maintaining the Yellowstone seismic network with the University of Utah Seismograph Stations (UUSS). We are saddened to report Dave's unexpected and untimely passing on February 11, just 8 days shy of his 58th birthday, and we would like to take this opportunity to celebrate his life and accomplishments.

Dave was born in Albany, New York, in 1960 and grew up just east of the Hudson River Valley. After receiving a BS degree in engineering from Duke University in 1985, he moved west to the University of Utah for a PhD in materials science engineering. Upon completion of his doctorate, Dave recognized that living in the Intermountain West offered him something new—namely to explore this new wilderness and mountain landscape and, most of all, to be his own boss.

The latter skill and his independent nature carried him throughout his career by simply asking, "what do you want to get done," and then saying "let me do it and do not bother me." Whatever was needed, it always got done. His first Utah job was shoveling snow off the roofs of lodges at Alta, Utah, and in the summers Dave explored the Colorado Plateau, the Green River, the Colorado River, the San Juan River, the Wind River Range, and the Tetons.

In the 1990s, Dave was hired at UUSS after demonstrating his commitment by volunteering to haul huge air-cell batteries (70 pounds each!) up steep hills to new seismic stations throughout Utah and Yellowstone. Dave had not taken any courses in electronics but was a very fast learner. As digital electronics began replacing analog systems, Dave quickly acquired the knowledge to install, repair and maintain the digital parts of the UUSS seismic network, keeping seismic monitoring in Utah and Yellowstone running smoothly for decades. Thanks in large part to Dave's hard work, the Yellowstone seismic network has evolved from its skeletal beginnings of a dozen old stations inherited from the U.S. Geological Survey to 35 modern digital seismic stations with 165 recorded channels and a high-reliability telemetry network.

Dave's contributions were not restricted to seismic monitoring. He also led the field construction of a network of permanent Global Positioning System (GPS) stations, and there are now about 25 sites in the region that are continuously measuring surface deformation. Both the GPS and seismic networks were located in the highest area of the Rocky Mountains, where winters can last 9 months, snow can be 10 feet deep, and temperatures have been known to drop to -50 Fahrenheit. Despite these challenges, most stations operate reliably year round.

These skills and experiences prompted many organizations to lean on Dave for assistance and advice. He was often called to help design new systems by the Incorporated Research Institutions for Seismology, University NAVSAR Consortium, the National Park Service, and the U.S. Geological Survey.

In addition to his tremendous skills, Dave also made friends with everyone he met. In Yellowstone, he knew all of the National Park Service personnel, interpreters, rangers, horse packers, and helicopter pilots. When staying in Park housing while doing field work, Dave would routinely cook up huge breakfast platters including eggs, tomatoes, garlic, potatoes, and onions (many of the ingredients for which were gathered from his own garden!) for not only his colleagues, but also nearby Park employees. The enticing smell wafted across the compound and brought neighbors by the dozen. He would also play his guitar on the porch and even in the field, serenading friends new and old.

Dave Drobeck will be sorely missed. His technical skills were beyond reproach, and his friendship is irreplaceable. We know more about Yellowstone because of Dave, and we are all better people for having known him.

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Behnaz Hosseini, geologist, and Jefferson Hungerford, park geologist, at the Yellowstone Center for Resources in Yellowstone National Park.

In the early nineteenth century, European settlers began exploring the lands of northwestern Wyoming—lands that had been known to Native Americans for millennia. The first organized expedition to the Yellowstone region was in 1869, and it laid the groundwork for the following Washburn-Langford-Doane Expedition of 1870 and Hayden Geological Survey of 1871. The two latter expeditions documented the dynamic and diverse hydrothermal features and played a pivotal role in convincing the U.S. Congress to pass legislation establishing Yellowstone National Park in 1872. With this, America's greatest idea came to fruition.

For over a decade after its founding, Yellowstone's succession of superintendents struggled to protect the park's natural features without adequate laws or resources. Congress did not allocate funds for an effective administration, and so in 1886 the Secretary of the Interior summoned the U.S. Army to take charge of Yellowstone. Three decades later, the Organic Act of 1916 established the National Park Service, giving Yellowstone the centralized administration required to protect park resources and provide educational experiences for visitors.

Of the eight Yellowstone Volcano Observatory member agencies, the NPS is the "boots on the ground" presence in Yellowstone. As was mentioned in an earlier Yellowstone Caldera Chronicles column, it may be tempting to imagine a legion of scientists stationed at several lookouts over the Yellowstone Caldera. The reality, however, is different but no less compelling: a team of geologists working in the Yellowstone Center for Resources in Mammoth, WY. Due to an on-site presence, the NPS affiliates of YVO are primed to repair inoperative equipment (e.g., seismic stations, data loggers, etc.) and provide updates on geologic activity within the park.

The Geology Program at the Yellowstone Center for Resources is tasked with research into and preservation of Yellowstone's hydrothermal features. In accordance with the Code of Laws of the United States, a long-term monitoring program was established to initiate a systematic approach to monitoring the park's hydrothermal features. The cornerstone of Yellowstone's monitoring program is the acquisition of temperature data from hydrothermal areas using both ground-based and airborne methods.

The monitoring program deploys and maintains data loggers with thermal sensors in the runoff channels of geysers in the Upper Geyser Basin, Lower Geyser Basin, and Norris Geyser Basin. By recording temperature at 30- to 60-second intervals, the data loggers provide indications of when geysers have erupted. In other words, when recorded temperatures exceed a certain baseline for a certain duration, a geyser eruption is implied. This method allows us to continually record the activity of specific geysers and thereby gain insight into the dynamics of the underlying hydrothermal system.

Traditionally, the monitoring program has also acquired 1 meter resolution and 1 °C accuracy thermal infrared imagery using an equipped helicopter. As described in last week's column, objects on Earth's surface—such as hydrothermal features—emit energy that is a function of the object's temperature. Although hydrothermal features are not hot enough to emit visible light, they do emit thermal infrared light that can be detected by specific sensors. This method allows us to detect changes in radiated heat from hydrothermal areas over time.

Yellowstone's alluring hydrothermal features continue to draw millions of visitors to the park every year. While visiting Yellowstone's hydrothermal areas, it is crucial to remember that they are as dangerous as they are striking. Please be cautious while viewing these features, and remain on boardwalks and designated trails while you enjoy the world's first national park!

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from R. Greg Vaughan, research geologist with the U.S. Geological Survey.

A lot of heat is released from Earth's surface at Yellowstone. The evidence of this heat flow includes thermal features like hot springs, geysers, mud pots, and fumaroles. Tracking the temperatures and sizes of thermal areas is critical for monitoring Yellowstone's hydrothermal activity, and also for understanding and preserving these spectacular features. But how do scientists accomplish this task, given that there are more than 10,000 individual thermal features spread out over a large and mostly inaccessible area within Yellowstone National Park?

The characteristics of Yellowstone's thermal features change with time, due to both natural processes and human activities. For example, as was discussed last week, there are occasional thermal disturbances at Norris Geyser Basin that are characterized by increased ground temperatures, changes in the eruption frequency and discharge rates at geysers and hot springs, and sometimes the formation of new features. In 2003, a portion of the hiking trail around Norris Geyser Basin was temporarily closed for safety reasons due to increased ground temperatures in areas near the trail that were previously cool.

Various human activities can also impact Yellowstone's thermal features, including vandalism (throwing objects into the thermal features) and the development of infrastructure (buildings, roads, and boardwalks). To recognize changes and understand the causes, we must continuously monitor these thermal areas.

Temperature is one of the key characteristics to monitor. Some of Yellowstone's thermal features, like those at Norris Geyser Basin, are continuously monitored with temperature sensors. However, it is not feasible to place temperature sensors and data recorders in every thermal feature in the Park. Fortunately, there is another way.

Everything that has a temperature emits energy into its surroundings, and the characteristics of this emitted energy are primarily a function of the object's temperature. This is the basis for how we can measure the temperature of a surface without being in contact with it—a technique called thermal infrared remote sensing.

If something is hot enough, it glows with light that we can see with our eyes. The temperature of water or steam in Yellowstone's thermal features is not hot enough to glow with visible light, but it glows (or emits radiation) in the thermal infrared part of the electromagnetic spectrum. We can't see thermal infrared light with our eyes, but we can build instruments that are sensitive to that energy. When you put an instrument like this on a satellite, you can make a thermal infrared temperature map of large areas, like Yellowstone.

One of the advantages of satellite-based thermal infrared remote sensing is that you can view nearly all of the thermal areas in the Park at once. But there also challenges and limitations to satellite remote sensing. For example, the temperature of Yellowstone's thermal areas is often not much higher than the temperature of the surroundings during the day because the Sun heats the Earth's surface. Using thermal infrared images that are acquired at night minimizes the influence of the Sun, allowing us to estimate just the geothermal component of the temperature.

Another technical challenge is that thermal infrared images from satellites tend to have low spatial detail. For example, the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) instrument on board NASA's Terra satellite records thermal infrared images with pixels that are 90 meters (about 300 feet) on a side. In other words, the largest thermal feature in the Park, Grand Prismatic Spring, is about the size of a single pixel. Nevertheless, ASTER thermal infrared images of Yellowstone have enough detail to make thermal area maps that are comparable to maps made from ground-based work. This is especially important because satellite images can provide information about areas that are not easily accessible.

Overall, research in thermal infrared remote sensing of Yellowstone has helped assess and update maps of the Park's thermal areas, created new thermal anomaly maps, estimated the geothermal heat output, and established background thermal patterns. Examination of how these maps change over time will provide important evidence for how both natural and human-induced processes affect some of Yellowstone's most iconic features.

For more information on mapping Yellowstone's thermal areas from space, check out Scientific Investigations Report 2014-5137.

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Jennifer Lewicki, research geologist with the U.S. Geological Survey in Menlo Park, CA.

Ever wonder what makes the Norris Geyser Basin in Yellowstone National Park so special? It turns out that the basin not only boasts the hottest temperatures and largest changes in hydrothermal (hot water) activity in the National Park, but is also home to Steamboat Geyser, which erupts to unmatched heights of up to 100 m (328 ft).

Norris Geyser Basin is also changing all the time, which makes it one of the most interesting thermal areas in the Park. These changes can involve unusual boiling, chemical changes to water, variations in spring activity, and increases in acidity and cloudiness of certain hot springs and geysers. A recent example is activity of Echinus Geyser, which, for a few weeks during October-November 2017, erupted every 2-3 hours, instead of its more usual intermittent activity.

A more noteworthy change occurred in 2003, when the southern part of Norris Geyser Basin, known as the Back Basin, attracted the attention of both scientists and visitors. Dramatic increases in hydrothermal activity occurred over a period of several months. Ground and water temperatures rose, water in some thermal pools boiled away and left hissing steam vents, new mud pots (depressions filled with boiling acidic water and mud) formed, and vegetation died and burned. Porkchop Geyser, inactive since 1989, increased markedly in temperature and then sprang back to life in an eruption. These changes motivated increased monitoring of seismicity and deformation by University of Utah scientists, and Yellowstone National Park ordered the temporary closure of the Back Basin to visitors to protect the public and park staff from hazards that could result from unusually high ground and water temperatures. It is still a mystery as to why the 2003 increase in hydrothermal activity was so extreme.

Norris Geyser Basin also hosts several craters that reach up to 100 m (328 feet) in diameter. These craters were formed during hydrothermal explosions that ejected boiling water, mud and rocks. The most recent of these events happened when Porkchop Geyser exploded unexpectedly in 1989, throwing boulders up to 1 m (3 feet) in diameter more than 66 m (216 feet) from the geyser. Although no one was injured in the explosion, it served as a reminder of the sudden and unpredictable hazards these events can pose.

Since Norris Geyser Basin is such an active and hot area of the Park, Yellowstone Volcano Observatory (YVO) scientists use an array of equipment to monitor hydrothermal activity. Data from these instruments help us to identify changes that occur before geyser eruptions, boiling episodes, or hydrothermal explosions, which will aid in minimizing impacts due to future hazardous situations. As related in previous columns, seismic instruments and Global Positioning System (GPS) receivers are used to measure ground movements that occur when water and gas flow in the subsurface, but the unique nature of the geyser basin requires more detailed work.

The Norris Geyser Basin is host to an array of temperature sensors that monitor changes in the flow of hot water out of the ground. These data can be accessed on YVO's monitoring webpage (zoom in to the Norris area and click on any of the thermometer icons to see plots of temperature at those stations over time). YVO also measures water chemistry of samples taken from hot springs and geysers to track their origins and underground flow paths, and heat flow is tracked by thermal infrared instruments on both aircraft and satellites. Many of these datasets are described in USGS data releases or publications about gas and water samples, gas and thermal samples from a 2016 temporary experiment, and satellite and ground-based thermal mapping. In the summer of 2018, new instruments are planned for continuous measurement of heat and gas emissions from Norris Geyser Basin.

Together, the array of information obtained from this diverse monitoring toolset should shed light on the potential causes of hydrothermal variations in Norris Geyser Basin and mitigate related hazards in the future. More information on Yellowstone's fascinating Norris Geyser Basin can be found at: https://pubs.usgs.gov/pp/1456/.

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Mike Poland, USGS research geophysicist and YVO Scientist-in-Charge, and Jamie Farrell, assistant research professor with the University of Utah Seismograph Stations and YVO Chief Seismologist.

Over the past several days, an earthquake swarm has been ongoing at Yellowstone. Before you read any more, keep in mind that swarms like this account for more than 50% of the seismic activity at Yellowstone, and no volcanic activity has occurred from any past such events. As of the night of February 18, over 200 earthquakes have been located in an area ~13 km (8 mi) NE of West Yellowstone, Montana. Many more earthquakes have occurred, but are too small to be located.

Does the location for this swarm sound familiar? It should... This is approximately the same place as last summer's Maple Creek swarm, which included about 2400 earthquakes during June-September 2017. In fact, the current swarm may be just a continuation of the Maple Creek swarm, given the ongoing but sporadic seismicity in the area over the past several months.

The present swarm started on February 8, with a few events occurring per day. On February 15, seismicity rates and magnitudes increased markedly. As of the night of February 18, the largest earthquake in the swarm is M2.9, and none of the events have been felt. All are occurring about 8 km (5 mi) beneath the surface.

What is causing this swarm seismicity? And why do swarms always seem to be happening in this part of Yellowstone National Park? A view of historical earthquakes in the region shows that the area is a hotbed of seismicity.

The University of Utah Seismograph Stations, which is responsible for seismic monitoring in the Yellowstone region, uses a standard definition of an earthquake swarm—an increase in earthquake rates within a given area over a relatively concentrated period of time without a single large "mainshock."

Swarms reflect changes in stress along small faults beneath the surface, and generally are caused by two processes: large-scale tectonic forces, and pressure changes beneath the surface due to accumulation and/or withdrawal of fluids (magma, water, and/or gas).

The area of the current swarm is subject to both processes. The largest historic earthquake in the region, the 1959 M7.3 Hebgen Lake event, was due to faulting that has its ultimate cause in the fact that the western United States is being pulled and stretched apart—this is what results in the "basin and range" topography of much of the region. But we also know that there is a tremendous amount of fluid in the subsurface, including hydrothermal water and gases that come to the surface at nearby Norris Geyser Basin—the hottest thermal area in Yellowstone National Park!

The current and past earthquake swarms reflect the geology of the region, which contains numerous faults, as well as fluids that are constantly in motion beneath the surface. This combination of existing faults and fluid migration, plus the fact that the region is probably still "feeling" the stress effects of the 1959 earthquake, contribute to making this area a hotbed of seismicity and swarm activity.

While it may seem worrisome, the current seismicity is relatively weak and actually represents an opportunity to learn more about Yellowstone. It is during periods of change when scientists can develop, test, and refine their models of how the Yellowstone volcanic system works. Past seismic swarms like those of 2004, 2009, and 2010, have led to new insights into the behavior of the caldera system. We hope to expand this knowledge through future analyses of the 2017 and 2018 seismicity.

The earthquakes, too, serve as a reminder of an underappreciated hazard at Yellowstone—that of strong earthquakes, which are the most likely event to cause damage in the region on the timescales of human lives. As recently as 1975 there was a M6.5 event in the area of Norris Geyser Basin.

In future columns, we will be sure to share the results of research into Yellowstone's seismic swarms. We will also keep you informed about current earthquake activity, both in this column and through our monthly updates. Stay tuned!

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Mike Poland, geophysicist with the U.S. Geological Survey and Scientist-in-Charge of the Yellowstone Volcano Observatory.

If you've been paying attention to monitoring data from Yellowstone or reading the Yellowstone Volcano Observatory (YVO) monthly updates, you might have noticed a recent change in how the ground around the Norris Geyser Basin is moving. This ground motion, called deformation, is one of the primary indicators of activity within Yellowstone's magmatic and hydrothermal systems. In December, deformation data indicate that the Norris Geyser Basin experienced a "hiccup," probably due to changes in hydrothermal fluids in the subsurface.

As last week's column reported, surface deformation can be monitored by many types of instruments, including borehole strainmeters, borehole tiltmeters and Global Positioning System (GPS) stations. GPS is one of the best ways of measuring long-term deformation and is used at volcanoes around the world. At Yellowstone, about 15 GPS stations are operating within the National Park, and many more are located in the surrounding region. These instruments track the ups and downs of the region in great detail, capturing numerous episodes of changing ground motion over the past several years.

Since 2015, deformation of Yellowstone has been largely consistent. GPS stations in the caldera indicate downward motion (subsidence), while stations near the Norris Geyser Basin show upward motion (uplift) of that area. Rates of subsidence and uplift have been small—approximately a few centimeters (about an inch) per year.

In early December, however, the pattern at Norris changed—the GPS station located closest to the geyser basin, named NRWY, suddenly began to record subsidence. Over the next 2-3 weeks, that station subsided by about 2 cm (almost 1 inch). By the end of December, the subsidence had stopped, and uplift resumed.

GPS stations outside the area could "sense" the Norris subsidence. Nearby stations began moving toward Norris, being drawn in by the subtle downwarping of the surface there.

This is not the first time a sudden change in deformation has occurred at Norris. In late 2013, the area began uplifting rapidly, accumulating 5 cm at the NRWY GPS station after just a few months. The uplift abruptly switched to subsidence on about March 30, 2014—the same day of a M4.8 earthquake in the area (the largest earthquake to have occurred in Yellowstone since 1980!).

By the end of 2014, the subsidence had returned Norris to its previous levels. Scientists believe that the sudden episode of uplift was caused by accumulation of hydrothermal fluids beneath the region, and that the earthquake represented the rupturing of a "seal" or other blockage. After the rupture, the fluids were able to drain from the system, and the surface subsided.

It is possible that the December 2017 subsidence represents a similar process. The uplift could be caused by hydrothermal fluids accumulating behind a blockage in the subsurface. This blockage was breached and allowed some fluids to drain, resulting in the subsidence, but then reestablished itself by the end of the month, and uplift resumed. Unlike the 2014 episode, however, there were no significant earthquakes in the Norris area at the time of the change in deformation.

Despite the recent "hiccup" at Norris, overall deformation of the caldera did not change. GPS data show that subsidence there continued at the same rates as have been measured since 2015. And the activity is not a signal of a potential eruption, but rather reflects the dynamic and ever-changing nature of Yellowstone's hydrothermal system.

If you would like to follow the Yellowstone deformation story yourself, all GPS data from the region are publically available. You can find plots by clicking on the stars that indicate GPS stations on the YVO Monitoring page, by zooming in to the region and clicking on GPS stations via the UNAVCO GPS station map interface, or by zooming in on the Yellowstone region and clicking on individual stations on the Nevada Geodetic Laboratory interactive map.

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from David Mencin and Glen Mattioli, geodesists with UNAVCO, Inc., in Boulder, CO.

We all know what it is like to experience strain. The pressures of everyday life can leave you feeling contorted and stretched. It turns out, volcanoes are no different—they experience strain as well, and measuring that strain can help scientists understand a volcano's activity. Unlike you, when a volcano experiences strain it really does contort or stretch. The very subtle change in shape of subsurface rock is called deformation. It can be caused by a variety of forces, including changes in magma pressure or even in the amount of water in lakes at the surface. But how can you tell how much strain a volcano is experiencing? Fortunately, the Yellowstone Volcano Observatory (YVO) consortium includes UNAVCO, Inc. as a member organization, and they are experts at measuring strain.

UNAVCO, Inc., is a non-profit university-governed consortium headquartered in Boulder, CO. Scientists there are responsible for operating and maintaining equipment for measuring ground movement (deformation) at Yellowstone and throughout the western United States. Some of the tools used for this type of monitoring include the Global Positioning System (GPS), borehole tiltmeters, and borehole strainmeters. Borehole strainmeters are particularly sensitive to deformation of the ground surface, and so have an important role to play in monitoring activity of Yellowstone.

To detect strain within the subsurface, scientists measure the change in diameter or volume of a strainmeter—an extremely sensitive instrument that is permanently grouted in a borehole. At Yellowstone, strainmeters are installed from 100 to 250 m (328 to 820 ft) depth below the surface. Borehole strainmeters can detect changes on the order of four picometers—that's about one ten millionth of the width of a human hair and smaller than the width of a hydrogen atom!

Sometimes these tiny strain measurements yield big surprises. For example, Yellowstone strainmeters are sensitive enough to record surface waves on Yellowstone Lake. Here's the surprising part:?the strainmeters are hundreds of feet deep and up to 12.5 miles (20 km) away from the lake, yet these water waves can tell us something about Yellowstone's deep volcanic plumbing system.

It's not that Yellowstone's magma affects the water waves directly, but rather that magma in the crust affects the way the waves are measured at the strainmeters—the strain signal is larger than would be expected if the crust under Yellowstone were completely solid. Computer simulations show that a zone of magma under the caldera would amplify the wave motion—that's exactly what is measured by the strainmeters! These independent observations agree with other instruments at Yellowstone, like seismometers, that indicate a zone of semi-molten rock starting about 3 miles (5 km) beneath the surface. We say semi-molten because the entire zone contains only between 5 and 15% liquid rock that occupies small pockets of space between solid rock.

These findings are no cause for alarm. The measurements and the models that are based on them are examples of how sensitive instruments located on and just below the Earth's surface are helping us learn more about the deep secrets of Yellowstone and other volcanoes.

More information about Borehole Strainmeter Data Products can be found here.

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Deborah Bergfeld, research geologist with the U.S. Geological Survey.

If you've visited Yellowstone, you've probably noticed that some thermal areas have a distinctive smell. This is due to the gas that discharges from features such as geysers, mud pots, roiling pools and fumaroles. But why is it that some areas are "smelly"—like rotten eggs or crude oil—and other areas are odorless, despite the presence of distinctive plumes of vapor? The answer is in the chemical makeup of the gases.

Most of the gas emitted from Yellowstone's thermal features is steam (boiling water), which is often visible, especially on a cold morning. If we ignore the steam, the remaining gas is primarily carbon dioxide (typically > 90%) with minor additions of helium, hydrogen sulfide, nitrogen, oxygen, methane, ammonia and other trace gases.

Research on the chemistry of Yellowstone's gas emissions is driven by a need to better understand and monitor both the deep magmatic system and the overlying hydrothermal system. This research shows there are 3 primary sources of gas at Yellowstone: the deep magmatic system; shallower crustal (rock-related) sources; and the atmosphere. The gas that ultimately discharges at the surface may contain components from all of these sources.

Studies of gas emissions are further complicated by the fact that some gas components are found in more than one source. For example, helium and carbon dioxide are emitted by magma at all volcanoes, but can also be released from crustal rocks under the influence of heat. So how can you tell the difference between these sources of gas? One method is to determine the isotopic composition of some gas components which can tell the story about gas origins.

For example, prominent degassing features at the Mud Volcano thermal area north of Yellowstone Lake include large churning pools of muddy water and a long-lived a superheated fumarole—the hottest vent in the park at ~114°C (237°F). Hydrogen sulfide makes up about 0.15% of the gas emissions and accounts for the strong rotten egg odor that permeates the air. Helium concentrations at Mud Volcano are only about 0.002% of the gas, but isotopic analyses of the carbon dioxide and helium readily confirm the link to the magmatic system. In fact, the helium isotopes show that the Mud Volcano gases have the strongest magmatic signature of any of Yellowstone's thermal areas. This thermal area is located well within the Yellowstone Caldera, so the strong connection to magma is reasonable.

In contrast, seeps at Devil's Den, below Tower Fall along the Yellowstone River, emit gas with a tar-like organic odor of hydrocarbons tinged with ammonia. South of the Tower-Roosevelt junction, similar hydrocarbon-rich gases are found at Washburn Hot springs. At these sites, carbon and helium isotopes indicate that the magmatic gases are significantly diluted by gases formed from the thermal breakdown of organic matter in crustal rocks.

Nitrogen and oxygen in Yellowstone gas emissions are primarily derived from the atmosphere. These gases dissolve in the rain water that percolates from the surface down into the hydrothermal system. They are released back to the atmosphere as the heated water boils back up to the surface, where these odorless trace gases provide hints about subsurface water flow.

Studies of gases at Yellowstone are expanding rapidly as new methods are developed for long-term measurements of steam, carbon dioxide and hydrogen sulfide. Typically, gas samples are collected sporadically. One of the first quasi-continuous gas sensors was installed near Norris Geyser Basin during the summer of 2016, and in the summer of 2017 the equipment was placed on the Central Plateau. In 2018, there are plans to install Yellowstone's first continuously operating (year-round) gas sensor at Norris. Stay tuned to Yellowstone Caldera Chronicles for details on the results from these experiments, and more information about both smelly and non-smelly gases!

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Jamie Farrell, assistant research professor with the University of Utah Seismograph Stations and Chief Seismologist of the Yellowstone Volcano Observatory.

The Yellowstone region is one of the most seismically active areas in the United States, experiencing around 1,500 – 2,500 located earthquakes per year on average. The majority of these earthquakes are too small to be felt by humans but are detected by sophisticated seismological monitoring equipment. But when did seismic monitoring start in the region? And what sort of earthquakes have been recorded over the past several decades?

Interest in seismic monitoring of Yellowstone took off after the 1959 magnitude 7.3 Hebgen Lake earthquake, which was located just west of the park boundary and north of West Yellowstone, MT. The event occurred on August 17th, 1959, at 11:37 pm MST and is the largest earthquake to occur in historical times in the Intermountain West. The Hebgen Lake earthquake was responsible for 28 deaths and had a major impact on the hydrothermal systems of nearby Yellowstone National Park, including Old Faithful Geyser. The earthquake triggered a major landslide in Madison Canyon causing 50 million cubic yards of rock to fall to the canyon floor, damming the Madison River and creating Earthquake Lake. In addition, the earthquake triggered many smaller rockfalls in Yellowstone that blocked roadways. Major damage was sustained by many structures in nearby West Yellowstone.

Seismic monitoring in Yellowstone began in earnest during the early 1970's, when a seismic network was installed and operated by the United States Geological Survey (USGS). This network operated until the early 1980's when it was discontinued for budgetary reasons. The network was re-established and expanded by the University of Utah Seismograph Stations (UUSS) in 1984, and it has been operated by UUSS ever since. Over the years, the Yellowstone Seismic Network has been updated with modern digital seismic recording equipment, making it one of the most modern volcano-monitoring networks in the world.

Today, UUSS records data from 46 seismometers in the Yellowstone region. The data are transferred from Yellowstone to the University of Utah in real-time using a sophisticated radio and satellite telemetry system. Given that Yellowstone is a high plateau that experiences heavy snowfall and frigid temperatures much of the year, and that many of the data transmission sites are located on tall peaks, it is a challenge to keep the data flowing during the harsh winter months. It is not uncommon for seismometers to go down for short periods of time because the solar panels or antennas get covered in snow and ice. Sometimes, seismometers that go down during the winter cannot be accessed until the spring.

Since 1973, there have been over 48,000 earthquakes located in the Yellowstone region. Over 99% of those earthquakes are magnitude 2 or below and are not felt by anyone. During that time, there has been one magnitude 6 event—the 1975 M6.1 Norris earthquake located near Norris Geyser Basin (the largest earthquake ever located within Yellowstone National Park). There have also been 2 earthquakes in the magnitude 5 range, 29 earthquakes in the magnitude 4 range, and 379 earthquakes in the magnitude 3 range.

The most recent magnitude 4 event occurred on June 15, 2017, at 5:48 pm local time. The earthquake had a magnitude of 4.4 and was reported felt by over 120 people in Yellowstone National Park and the surrounding communities, including West Yellowstone, MT. The event was part of the Maple Creek Swarm (the 2nd largest swarm recorded in Yellowstone), a cluster of over 2,300 earthquakes that occurred in Yellowstone from June – September, 2017 (for more information, see the January 1, 2018, issue of Yellowstone Caldera Chronicles.

Earthquake swarms (earthquakes that cluster in time and space) account for about 50% of the total seismicity in Yellowstone and can occur anywhere in the Yellowstone region, but they are most common in the east-west band of seismicity between Hebgen Lake and the Norris Geyser Basin. Most swarms are small, containing 10-20 earthquakes, and short, lasting for 1–2 days. However, large swarms that can contain 1,000's of earthquakes and last for months do occur on occasion. Some of the larger swarms are:

The UUSS website serves up all located earthquakes and real-time images of the seismic data (as seen on webicorders). You can follow UUSS on Twitter (@UUSS_Quake_Info), to view earthquake information as it happens, and on Facebook where content is regularly added. Check out these feeds for more information about earthquake activity in one of the most seismically active regions in the country!

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Shaul Hurwitz, research hydrologist with the U.S. Geological Survey.

Have you ever wondered how Yellowstone Caldera was discovered, and how it was recognized as being the result of a massive volcanic eruption? In fact, the Yellowstone Plateau hosts three separate calderas, the youngest being the "Yellowstone Caldera". Our knowledge on how and when these three calderas formed is a result of many years of extensive field work and geologic mapping led by U.S. Geological Survey (USGS) scientist Bob Christiansen.

A caldera is large basin-shaped volcanic depression commonly formed when magma is withdrawn or erupted from a shallow underground reservoir. The removal of large volumes of magma results in loss of structural support for the overlying rock, thereby leading to collapse of the ground.

In the 1950s Joe Boyd, a doctoral student at Harvard University, carried out research on the rhyolite rocks in Yellowstone. Boyd recognized that some of the rhyolites were not lava flows, but rather tuffs (solidified deposits of ash that formed from explosive eruptions). He also identified a depression in the Yellowstone Plateau and suggested that it was related to the explosive eruptions. Boyd published his novel finding in a journal paper entitled "Welded tuffs and flows in the Rhyolite Plateau of Yellowstone Park, Wyoming". The causal link between the tuffs and the depression, however, remained unexplained.

Bob Christiansen was part of a USGS group that was tasked in 1965 with creating a comprehensive geologic map of the Yellowstone Plateau. Christiansen and his colleagues were asked to map the volcanic rocks that erupted during the Quaternary Period of Yellowstone, now recognized as the last 2.6 million years. The study was funded by several federal agencies including NASA, the National Park Service and the USGS. At the time, NASA was developing remote sensing instruments for satellites and needed test areas with good geologic maps to compare with the images captured from space.

Christiansen and his colleagues tried to understand when and how the volcano erupted, how much magma was vented, and where it went. Every year between 1966 and 1971 they spent three summer months in Yellowstone carrying out field work, often in very remote areas. In other times of the year, they analyzed aerial photographs, used microscopes to scrutinize slices of sampled rocks thinned to less than the width of a human hair (called "thin sections"), and measured the chemical composition of the rocks and their relative ages.

By 1972 the bulk of the geologic mapping was complete, and Christiansen and his colleague Dick Blank published the first report describing the volcanic history of the Yellowstone Plateau. Their findings revealed many of the details of Yellowstone's explosive volcanic past. They found that three large explosive eruptions were associated with formation of calderas. Based on potassium-argon dating by their USGS colleague John Obradovich, it was determined that the three large explosive eruptions occurred at 2.0, 1.2 and 0.6 million years ago. More recent results using more accurate dating methods revealed that these caldera forming eruptions took place 2.08 1.30, 0.63 million years ago.

Christiansen continued his work in Yellowstone for the next 25 years, mainly focusing his research on specific questions related to the volcanic history. His goal was to improve our understanding of the possible conditions that led to large eruptions. The comprehensive description of Yellowstone's volcanic history and the geologic map were published in 2001.

During that same year, Bob Christiansen became the founding Scientist-in-Charge of the Yellowstone Volcano Observatory. After 40 distinguished years with the USGS, he retired in 2004. Bob has described his time at Yellowstone in this interview. Today, Bob still continues his research as a scientist emeritus with the USGS in Menlo Park, California.

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Michael Poland, geophysicist with the U.S. Geological Survey and Scientist-in-Charge of the Yellowstone Volcano Observatory.

To most people, the idea of a volcano "observatory" conjures image of a building that looks out at an active volcano, staffed by scientists who keep watch using an array of instrumentation. In many places, this is true. For example, the Hawaiian Volcano Observatory—one of the 5 observatories located in the United States—features a tower with a commanding view of the summit of KILAUEA, the most active volcano on Earth. In some parts of the world, having an observatory building with a good view of a volcano is critical for making measurements and collecting observations. The Yellowstone Volcano Observatory (YVO) is different, however—there is no building, and its diverse team of scientists is spread across the western United States.

One might expect that YVO is a scientist-staffed physical facility located within or near Yellowstone National Park. After all, Yellowstone is the largest volcanic system in the world, and bears watching! In fact, there is no actual structure to house YVO. What's more, YVO is not simply an operation of the U.S. Geological Survey (USGS). Instead, it is a consortium of partners who share the goal of monitoring and better understanding Yellowstone's volcanic activity. These characteristics make YVO unique among the volcano observatories of the world.

Let's start with the lack of a building. That may seem odd, but there is no need for an on-site presence. Yellowstone is far too vast for a single point to provide a suitable observation post. The only place with a commanding view of the area is on top of Mount Washburn (elevation 10,243 feet), and that spot is not accessible most months of the year due to Yellowstone's harsh winters.

The volcanic system has also not experienced an eruption of magma for about 70,000 years, when the most recent lava flow was emplaced. Visual observations of volcanic activity are therefore not critical for monitoring Yellowstone's activity. Regardless, the National Park Service staff, as well as some private citizens, provide abundant on-site observations of thermal and geyser activity, so there is certainly a "boots on the ground" presence at Yellowstone.

Finally, Yellowstone is host to a vast array of instrumentation that is constantly recording data that can be accessed via the Internet. This includes not only the seismic and deformation stations, but also records of water levels and chemistry, temperatures of thermal areas, and other geological information. These data can be viewed by scientists across the country in real time with just a few clicks of a mouse, and without the need to travel to Yellowstone. Indeed, the YVO Scientist-in-Charge has never resided in the Yellowstone area. The park geologist, however, does live on site and represents YVO when needed.

This brings us to the second unique aspect of YVO—that it is not an operation run by USGS, but rather a consortium of agencies: USGS, the National Park Service, the University of Utah (which operates the Yellowstone seismic network), UNAVCO (which maintains GPS stations, borehole tiltmeters and strainmeters, and lake monitors within Yellowstone National Park), the University of Wyoming, the Montana Bureau of Mines and Geology, the Wyoming State Geological Survey, and the Idaho Geological Survey.

The consortium includes scientists with extensive experience in volcanology. The research and monitoring work accomplished by these scientists is critical to not only understanding what is happening beneath the ground, but also to determining whether or not any hazardous activity may be imminent. In the event of a crisis, all of the partners would come together in Yellowstone National Park to assess potential outcomes and provide expert guidance to emergency managers.

Although this non-traditional approach to a volcano observatory would not work everywhere, it has served YVO well since its founding in 2001. So the next time you think about YVO, don't think of a building. Rather, think about the large team spread across the western United States that is collaborating behind the scenes to provide the best and most current information about Yellowstone volcanism.

Welcome to the inaugural issue of "Yellowstone Caldera Chronicles," a new weekly column of the Yellowstone Volcano Observatory (YVO). Each Monday on the YVO homepage, we'll post a new article that covers a different topic, including geology, history, current activity, and other subjects. The articles will be written by YVO scientists and others who study Yellowstone's volcanic system.

The publication of the first issue of Yellowstone Caldera Chronicles on New Year's Day of 2018 provides an excellent opportunity to review the activity that occurred in Yellowstone over the past year. And what a year it was!

2017 began calmly enough. In the first several months of the year, only a few hundred earthquakes were located by the University of Utah Seismograph Stations, which has the lead in monitoring seismic activity in the Yellowstone region. This trend continued the low earthquake rates of 2015 and 2016, during which only about 1,000 earthquakes were located per year (typically, between 1,000 and 3,000 earthquakes are located in any given year).

All of this changed on June 12, when the Maple Creek earthquake swarm began on the west side of the Park, a few miles north of West Yellowstone, Montana. Over the ensuing three months, about 2,400 earthquakes were located by the University of Utah Seismograph Stations (many more earthquakes occurred but were too small to be located). The swarm lasted until early September, and small bursts of seismicity occurred in the same area in late September and late October. The largest event in the sequence was an M4.4 event on June 16.

Additional swarms of earthquakes occurred outside the Yellowstone area, near Lincoln, Montana, and Soda Springs, Idaho. These swarms were each kicked off by widely felt M5+ earthquakes, but the seismicity is not related to the Yellowstone magmatic system. Instead, the earthquakes are caused by faulting associated with tectonic extension of the western United States.

Overall for the year, over 3,300 earthquakes, including about 20 that were felt, were located in the Yellowstone region, making 2017 one of the most seismically active years ever recorded. Almost 80% of all the earthquakes that were located occurred as part of approximately 13 swarms, of which the Maple Creek swarm was by far the largest. But was that swarm the largest ever recorded at Yellowstone?

In fact, the 2017 Maple Creek swarm comes in a distant second to that of 1985. In that year, an earthquake swarm also near West Yellowstone, Montana, lasted for 3 months and included over 3,000 located earthquakes, with the largest reaching M4.9. If today's monitoring system had been in place in 1985, it is likely that many more earthquakes would have been located. The 2010 Madison swarm, just southwest of West Yellowstone, is now the third largest swarm ever recorded, with about 2,300 located events.

Interestingly, the 1985 and 2010 swarms were associated with a change in deformation style of the caldera. During both years, the caldera switched from uplift to subsidence, suggesting that the swarms were associated with a release of fluids from the caldera region.

In 2017, however, there was no significant change in deformation at the time of the swarm. Throughout most of the year, the caldera subsided and the area around Norris Geyser Basin continued to uplift, as indicated by numerous continuous Global Positioning System stations in the region. Both caldera subsidence and Norris uplift have been ongoing since 2015. In early-December, however, that pattern began to change, with subsidence beginning at Norris. Whether this pattern will continue remains to be seen.

Instead of being related to fluid migration, it is also possible that the Maple Creek earthquake swarm is a lingering effect of the 1959 M7.3 Hebgen Lake earthquake—the largest earthquake ever recorded in the Yellowstone region. Future research will help to unravel this story.

We will be sure to update you on the results of our research in this column, so stay tuned for more information in the months to come. In the meantime, we hope you enjoy this recurring column, and we look forward to sharing interesting stories and new information every week.

The many members of the YVO consortium wish you and your loved ones a wonderful start to 2018. Happy New Year!

YVO scientists were busy in October 2017. During that month, a number of field measurements were completed in Yellowstone National Park, and some instruments that had been recording data throughout the summer were recovered before the onset of the harsh Rocky Mountain winter. This included 12 semipermanent Global Positioning System (GPS) stations that had been in place since the spring—part of an annual campaign, now 10 years and still running, aimed at improving our understanding of how the ground deforms due to magmatic and hydrothermal activity in the Yellowstone region.

Together with frequent earthquakes, vigorous hydrothermal activity, and abundant emissions of volcanic gases, relatively slow movements of the ground surface attest to ongoing activity in the vast magmatic-tectonic system beneath Yellowstone National Park. Imperceptible to the naked eye, episodes of uplift, subsidence, and stretching or contraction of the surface are monitored by repeated surveys and networks of sensitive instruments operated by YVO and its partners. The process is called deformation because it changes the shape of the land surface in subtle but detectable ways. Since the first leveling survey along Park roads in 1923, the central part of the caldera floor has moved up nearly 1 meter (about 3 feet). But the uplift hasn't been steady. Annual leveling surveys from 1983 to 2007 revealed periods of subsidence lasting up to a decade. More recently, scientists using a satellite radar technique called InSAR have discovered that both the pattern and rate of surface deformation change over time. Such movements are part of normal background activity at one of Earth's largest active magmatic systems.

One of the tools that scientists use to keep track of surface deformation is the same GPS technology that you might use to navigate while driving your car. With specialized equipment and data processing techniques, the location of a GPS monitoring station can be measured very precisely, to within about 1 millimeter (less than the thickness of a dime). YVO and its partners, the University NAVSTAR Consortium (UNAVCO) and University of Utah, have installed a network of more than two dozen such stations in and around Yellowstone National Park to track surface deformation. The stations operate continuously, and data are processed at several locations to obtain daily positions. Small movements of the stations with respect to one another reveal the pattern of surface deformation over time.

The continuous GPS network cannot cover all areas in Yellowstone National Park, so YVO scientists have devised a less invasive GPS technique called semipermanent GPS (SPGPS). As the name implies, SPGPS stations are temporary. A network of SPGPS stations is installed each year from spring through autumn, avoiding months with heavy snowfall that can bury GPS antennas. This arrangement allows SPGPS stations to be smaller than continuous GPS installations—a distinct advantage in ecologically sensitive areas like Yellowstone. The trade-off, of course, is that SPGPS stations only acquire data when they are deployed. Despite the winter data gaps, SPGPS data have been useful for tracking movements of the caldera floor and an active area along the north caldera rim centered near Norris Geyser Basin. For example, on March 30, 2014, a magnitude 4.8 earthquake—the largest Yellowstone quake in 34 years—shook the Norris area. Nearby SPGPS stations that had been deployed only a few days earlier recorded a sudden reversal from uplift to subsidence that coincided with the timing of the quake. Combined with data from the continuous GPS network and InSAR observations, the SPGPS results helped to identify the location and depth of the deformation source. SPGPS may also prove useful for investigating the summer 2017 earthquake swarm north of West Yellowstone, MT. A SPGPS station at Horse Butte is only 15 km west of the swarm's center. Analyzing the data from the station, which was recovered in late October, might prove useful to understanding the cause of the earthquakes and any associated ground motion. Stay tuned—we'll post details about the 2017 SPGPS results to the YVO website over the winter!

On September 1, I succeeded Jake Lowenstern as the Yellowstone Volcano Observatory (YVO) Scientist-in-Charge. To say I have some big shoes to fill is an understatement. During his 15 years in the position, Jake oversaw the growth of YVO into a collaborative consortium of eight organizations, helped guide the expansion of geophysical and geochemical monitoring, encouraged (and also initiated!) a broad array of research, and tirelessly advocated for communicating and sharing the wonders of Yellowstone with the world. I can never replace Jake, but I hope to prove an effective steward of his efforts, and I will continue to advance the goal of improving our knowledge of the inner workings of Yellowstone as well as other volcanic systems in the United States and, indeed, around the world.

My first visit to Yellowstone National Park was 30 years ago, when my family gathered for a reunion camp out at Grant Village on the shores of West Thumb. The memories of that experience are vivid, from waiting patiently for Old Faithful to erupt, to contributing to a "bison jam" in Hayden Valley. In subsequent years, I visited the Park on numerous occasions, both on vacation and professionally as I pursued a career in Earth science. The Park captivated my imagination and helped to stimulate my interest in geology, and I am pleased to now be able to play a small role in helping to grow our understanding of Yellowstone's behavior.

My USGS career began in 2002 at the Cascades Volcano Observatory, where I was tasked with developing a capability for assessing ground deformation using radar data from orbiting satellites. A high point of my time in the Cascades was in 2004, when I was part of the team that responded to the reawakening of Mount St. Helens—my first experience in responding to a volcanic crisis. I also was able to make numerous trips to Yellowstone as part of USGS efforts to map ground deformation throughout the caldera system. This work had me collaborating closely with Dan Dzurisin, whose studies have redefined how we view the behavior of volcanic calderas.

In 2005, I moved to the Island of Hawaii, where I spent 10 years conducting research as a staff member at the Hawaiian Volcano Observatory. I was very lucky to not only work with many talented scientists, but also to experience some incredibly dynamic volcanic events and earthquakes—the M6.7 Kiholo Bay earthquake in 2006, the start of Kilauea's currently ongoing summit eruption in 2008, and a "curtain of fire" fissure eruption at Kilauea in 2011, to name a few. My scientific explorations, done in collaboration with numerous Observatory and university scientists, focused on figuring out the patterns of ground deformation over time (especially using satellites), understanding the changing rates of magma supply to the volcanoes of Hawaii, and using microgravity measurements to map changes in subsurface magma storage.

I returned to the Cascades Volcano Observatory in 2015, resuming my work using satellites to track ground deformation, implementing gravity measurements in the region, and generally aiming to better understand the behavior of volcanoes in Washington and Oregon.

In my new role with YVO, I plan to apply the lessons learned over my 15-year USGS career to research in Yellowstone. This past summer, I began working with colleagues from the US and other countries to use gravity as a means of better understanding the nature of the subsurface fluids (gas, water, and magma) that drive seismicity and deformation of the Yellowstone system. This effort continues work begun decades earlier by Bob Smith and co-workers, and is leading me to new collaborations with fellow YVO scientist Jamie Farrell and others at the University of Utah. My interest in magma supply to Hawaiian volcanoes is also relevant to Yellowstone (both are hotspot systems), and I plan to examine a variety of data to investigate how magma is supplied to the reservoir beneath the caldera.

In addition, I hope to continue the expansion of monitoring systems at Yellowstone, augmenting the current network with additional geochemical and geophysical sensors that will help to address such important questions as: What processes drive the frequent earthquake swarms in and around the caldera? What causes abrupt changes in surface deformation over time and space? What is the nature of Yellowstone's magma reservoir?

Relaying information about hazards, especially in collaboration with the National Park Service (including park geologist Jefferson Hungerford and the team at the Yellowstone Center for Resources), will continue to be a priority. Everyone knows of the catastrophic eruptions that have occurred as part of Yellowstone's geologic past, but far more likely to impact the region on human time scales are hydrothermal explosions. Small explosions take place every few years, while a few larger explosions have occurred in the past ~10,000 years, leaving craters that dot portions of the Park's landscape.

I am also optimistic that we can grow our understanding of other volcanic fields in the western United States, including those in Arizona, Utah, New Mexico, and Colorado, over which YVO has operational responsibility.

A particularly attractive aspect of my new job is the opportunity to interact with both the public and other scientists. YVO is unique in that it is a consortium of organizations, including the USGS, Yellowstone National Park, the Universities of Utah and Wyoming, UNAVCO, and the state geological surveys of Wyoming, Montana, and Idaho. The ability to collaborate with scientists of these, and other, institutions is, frankly, a thrilling prospect. No less enticing is the opportunity to share my enthusiasm for Yellowstone, and volcanology in general, with all of you. As my friends and colleagues can no doubt attest (perhaps not without a touch of sarcasm), I enjoy talking. A lot.

With the introduction behind us, time to get to work—there is much to learn! We will do our very best to update the YVO website and USGS Volcanoes Facebook and Twitter feeds with information on the status of ongoing research and interesting geologic activity. In the meantime, I hope to see you around the wonderland that is Yellowstone National Park!

This week I'm stepping down as the Scientist-in-Charge of the Yellowstone Volcano Observatory (YVO). I've held this role since 2002, and it's been an incredibly rewarding 15 years. Recently, I was offered the opportunity to lead the Volcano Disaster Assistance Program (VDAP), where I'll work with my USGS colleagues to assist volcano observatories in developing countries that face daunting volcanic risk. VDAP is a vibrant program created 31 years ago, and is arguably the premier team of volcano scientists on the globe.

It's not without sadness, though, that I will move on from my work at Yellowstone. I've cherished my many visits to the park, starting with trips as a child and young adult, and later, as a geologist. I've worked with outstanding scientists from our YVO partners and indeed from around the world. I've had the incredible good fortune to travel to remote areas around the park to research the variations in gases that can inform our understanding of the subsurface beneath Yellowstone. Our work has gone smoothly, largely due to the staff of Yellowstone National Park, which is incredibly dedicated to ensuring that visitors and researchers alike get the most of their visits and leave Wonderland without incident. For the many Yellowstone lovers out there in the world, I wanted to take a little time to say a proper goodbye, to recount how we got to the present day, and to reflect on some of what's been learned.

Though I'm sad to be moving on, I'm delighted that the observatory will be in excellent hands. Mike Poland will take over as Scientist-in-Charge. Mike has been with the USGS for fifteen years, and is a veteran of both the Cascades and Hawaiian Volcano Observatories. He is an expert in volcano deformation, and in using satellites to track the subtle ups and downs of volcanic terrain that can indicate magma movement below. That's a very useful expertise at Yellowstone, where earthquakes and ground deformation are the dominant monitored signals. Speaking of earthquakes, Jamie Farrell, at the University of Utah has taken over much of the responsibility for the Yellowstone Seismic Network. After many years working with his mentor Bob Smith, Jamie has gained unparalleled experience in studying Yellowstone earthquakes and the deep magma below. In fact, Jamie was responsible for most of the colorful images of the Yellowstone magma reservoir that you've probably seen on the internet. Jefferson Hungerford is the brand new Park Geologist at Yellowstone. His expertise in volcano science, industrious nature, and remarkable good cheer will serve him well as the park focal point for all things geological.

Now a bit of the history…In 2002, during my first weekend as Scientist-in-Charge, the Denali Earthquake struck in Alaska. Surprisingly, when the surface waves hit Yellowstone, some 2000 miles away, it induced hundreds of local earthquakes, many of which were felt around Yellowstone Lake. Fortunately, University of Utah Professor Bob Smith already had worked at Yellowstone for ~30 years and was able to put the activity in context and to help explain the activity to the staff of Yellowstone National Park, to me, and to Hank Heasler, who was also new in his role as the Park Geologist. This notable event threw me "in the deep end," and prepared me for the many earthquake swarms, uplift episodes, and thermal changes that followed over the next decade and a half.

In addition to Bob, I and my colleagues had the good fortune to be mentored by the generation of geologists who did the key research on Yellowstone's geologic past. Bob Christiansen of the USGS spent his summers in the 1960s and 1970s traipsing hill and dale to map out scores of lava flows and ash flow tuffs. He worked with colleagues using K-Ar dating techniques to reveal the age relations of these many events. Chris, as he's known, recognized that there were three massive explosive eruptions at Yellowstone that formed three separate calderas. He published the authoritative geologic map of Yellowstone, and served as the first Scientist-in-Charge of YVO in 2001 until he retired a year later. His contemporaries included the USGS's Ken Pierce, who deciphered much of the glacial history at Yellowstone and with Lisa Morgan traced the older volcanic systems of the Snake River Plain that preceded Yellowstone. Don White and his USGS protégées, Bob Fournier and Patrick Muffler, undertook the ambitious scientific drilling program in Yellowstone's thermal areas, mapping out the temperature and pressure gradients in the subsurface, and collecting core samples of the hydrothermal minerals that we still use as the basis for research projects today. Fournier continued his work at Yellowstone for decades, becoming one of the world's preeminent geochemists. Muffler wrote the first paper on Yellowstone's notorious hydrothermal explosion craters, which represent one of the more common hazards in the park. And of course Bob Smith of the University of Utah, is responsible for a wide swath of geophysical research ranging from Yellowstone earthquakes, to the depth and size of the subsurface magma reservoir, to heat flow and hydrothermal activity beneath Yellowstone Lake. I was incredibly fortunate to be able to learn from all these legends of Yellowstone, and to work with them to further our knowledge of the geologic history, current dynamic behavior, and potential for future activity.

The stage was set by the work of these USGS and academic researchers, as well as by fantastic park geologists such as George Marler, Wayne Hamilton and Rick Hutchinson. Though geologists were well acquainted with the Yellowstone story by the mid 1980s, it was another fifteen years before the public got wind of this amazing story. A 1999 BBC documentary, Supervolcano, interviewed Christiansen, Smith, and others, and captured the imagination of the public. In 2005, BBC and Discovery Channel combined efforts to create a docudrama of the same name. Over the following five years, a series of documentaries thoroughly saturated the market for Yellowstone Volcano, and set the stage for a decade of hyperbole and misinformation with the growth of the internet. One irony of this expansion of the Yellowstone geologic story, is that the work of the pioneering scientists has been lost from the public's mind. Most recent news stories present a simplified, and misunderstood summary of Yellowstone, without any mention of how we got our present knowledge. And the less people know about Yellowstone, or earth science, the more they tend to question the expertise of those who know it best.

Nevertheless, working at Yellowstone has been a tremendous pleasure, and we can take great pride in our accomplishments. Since 2002, we developed a monitoring plan, a hazards assessment, two successive response plans, an exercise to test our response plan, and numerous information statements and web articles to explain ongoing activity such as earthquake swarms and ground uplift. We installed borehole strainmeters and associated downhole seismometers thanks to the Plate Boundary Observatory. We spent almost $1M to expand the seismic and other networks through the American Recovery and Reinvestment Act. We installed miniature, radio-relayed temperature sensors at the Norris Geyser Basin. We expanded the observatory in 2013 to include eight partners, including the geological surveys of the three states that encompass Yellowstone. And we built a website and social media presence that provides detailed explanations of our work and current research efforts. And in our spare time, YVO researchers published well over 50 new research papers in the past 15 years that extend our understanding of the volcanic and hydrothermal system at Yellowstone.

In closing, I want to thank my colleagues for their generosity and friendship over an exceptional fifteen years. Most notable is Peter Cervelli, who has acted as Deputy Scientist-in-Charge for the past five years, but there are many, many others. Together, we've explored the volcano, discovered new phenomena, challenged each other's ideas, and reveled in our good fortune to be able to work at such an amazing place.

Seismic networks locate earthquakes by comparing the arrival times of seismic waves emanating from the earthquake location, or hypocenter. Very small earthquakes (less than a Magnitude 1) cannot be detected on distant seismometers and sometimes even well-located earthquakes may have horizontal and depth uncertainties of more than 0.5 km.

In order to more fully study a 2010 earthquake swarm on the Madison Plateau, in the northwest part of the Yellowstone Caldera, USGS seismologist David Shelly used a specific timeframe of seismic data and mathematical algorithms to detect and relocate tiny earthquakes. Shelly and his colleagues were able to recognize 8710 events, including many small events with magnitude as low as -1. By including these events, Shelly and his colleagues were able to understand more about the relative location of all the earthquakes and how the earthquakes migrated along the crustal fault during the 2010 swarm. The research was published in 2013 in the Journal of Geophysical Research, co-authored with colleagues form the University of Utah. Read more in the web article Taking a closer look at a Yellowstone earthquake swarm.

Natural geysers are rare on Earth; there are fewer than 1,000 worldwide, and about half of them are in Yellowstone National Park. Geysers, whose eruptions range from small bubbling pools, to roaring jets of water and steam that can reach a few hundred meters high, fascinate all who have the good fortune of witnessing one.

In a newly published paper in the "Annual Review of Earth and Planetary Sciences", U. S. Geological Survey hydrologist, Shaul Hurwitz and his coauthor, geology professor Michael Manga at the University of California, Berkeley, synthesize the current state of knowledge about geysers. The authors review past research, and point the way to answering future questions.

Because many of the processes associated with geyser eruptions are similar to those operating in volcanoes, understanding the mechanics of geysers and how they operate can lead to better understanding and predictions of volcanic eruptions.

Beginning November 7, and lasting two to four weeks, two exciting studies will take place while Yellowstone National Park is in between its summer and winter seasons. They are aimed at learning more about the shallow water system that fuels the famous hot springs, geysers, and other thermal features at Yellowstone. The first is a helicopter-borne electromagnetic study of geothermal areas near the Firehole River, along the Norris-Mammoth corridor, and at the north end of Yellowstone Lake. The second is a seismic study focusing on the area near Old Faithful. The need for these studies are a result of published recommendations from a 2013 scientific committee that formed with the goal to understand ways to reduce human impacts on the park's geothermal features and protect existing park infrastructure from encroachment of hot ground.

The U.S. Geological Survey (USGS), University of Wyoming, and Aarhus University, Denmark, will collaborate to study the groundwater system that feeds the iconic hydrothermal features of Yellowstone National Park. Airborne geophysical electromagnetic (EM) surveys are one of the unique tools that experts can use to examine and map subsurface location, size, shape, salinity and temperature of groundwater. The survey will map important properties of soils and subsurface rocks in order to learn more about Yellowstone's groundwater resources. Because it involves low-level helicopter flights that may disturb park visitors, the research was allowed after roads officially close, and before it opens for winter use.

The University of Utah, in collaboration with the University of Texas El Paso and the National Park Service, will place closely spaced quart-jar-sized, portable seismometers around the Upper Geyser Basin, focusing on the immediate area around Old Faithful Geyser. This is a continuation of a project started in November 2015 when a more general array was deployed for two weeks. The principal objectives of these deployments are to create an image of the shallow seismic velocity structure of the Upper Geyser Basin. The results will help the park service plan for engineering projects relating to developed structures in the area. In addition, data will help scientists better understand the underground fluid flow pathways and hydrothermal properties between geysers and hot springs of the Upper Geyser Basin, including Old Faithful. Importantly, the dense grid of seismometers deployed on the cone of Old Faithful will help us learn more about how the geyser acts before, during, and after eruptions.

Over the past few years, we've recorded interviews with a number of the scientists who did critical work revealing Yellowstone's volcanic past and present. Our latest installment includes two interviews with Dr. Ken Pierce, a glaciologist and geomorphologist who works today as an emeritus scientists with the USGS in Bozeman, MT. Pierce has written scores of important articles on the geology of Yellowstone, and these two videos give you a flavor of the man and his career.

Interested in supereruptions? This May 2016 talk by USGS scientist Larry Mastin summarizes how we model ash transport after volcanic eruptions, which was applied to some of the big eruptions in Yellowstone's past. The work follows on to Larry's 2014 publication that was summarized as a series of FAQs on our website. The lecture discusses Yellowstone and it's history, but it also discusses the broader study of ash plumes in the atmosphere and how researchers are keen to develop methods to estimate how and where ash will fall after big eruptions.

YVO staff contributed to a new USGS video entitled: "An Illustrated Guide to Reading a Seismogram." This off-beat video provides a short, introductory lesson on how the seismic plots are generated and the potential sources for "signals" on a seismogram.

If you're looking for additional insight on Yellowstone geology, three video interviews were added in September. USGS Video Producer Steve Wessells conducted interviews with some of the key USGS scientists who unlocked the secrets to Yellowstone's volcanic and geothermal history. Bob Christiansen, Patrick Muffler and Bob Fournier reminisce about their early careers working at Yellowstone in the 1960s and 1970s.

The likelihood of a volcanic supereruption from Yellowstone, or any other location on Earth, remains very low in any given year, yet the U.S. Geological Survey is frequently asked about the likely thickness and distribution of ash deposits if Yellowstone were to erupt. This prompted USGS scientists to use a new computer model called Ash3D to simulate the distribution of volcanic ash from a hypothetical large explosive eruption at Yellowstone. A research paper explaining the results was published in Geochemistry, Geophysics, Geosystems on August 27, 2014, and we have developed some FAQ to help explain the background to this study.

The researchers discovered that during very large volcanic eruptions, ash transport is dominated by a rapidly expanding umbrella cloud that results in significant distribution of ash upwind from the volcanic vent. "In essence, the eruption makes its own winds that can overcome the prevailing westerlies that normally dominate weather patterns in the United States," explained USGS geologist Larry Mastin, first author on the manuscript and co-developer of the computer model. "This helps explain the distribution from large Yellowstone eruptions of the past, where considerable amounts of ash reached the west coast." The authors also note that a fraction of an inch or less of ash is likely to be deposited at distances further than 1500 miles, such as on the east and west coasts of the United States. To learn more, please read our Frequently Asked Questions about the model and its application to Yellowstone.

Though we love doing research at YVO, we prefer it when the research is on topics geological rather than the origin of false rumors. Nevertheless, we have received enough concerned emails and phone calls that we've spent some time tracking down a few of the statements made on various "alternative Internet news sources."

1) First, everyone should know that geological activity, including earthquakes and ground uplift/subsidence is well within historical norms and seismicity is actually a bit low at present.

2) Concern over road closures is much overblown. There's been one road closure of a small side road – just over three miles long – that was closed for two days. As one can imagine, it is not easy to maintain roads that pass over thermal areas where ground temperatures can approach those of boiling water. Roads at Yellowstone often need repair because of damage by thermal features as well as extreme cold winter conditions.

3) The park has not been evacuated. This one is pretty easy to verify by everyone. If the Old Faithful webcam shows people, or if news articles are coming out about a hobbyist's remote control helicopter crashing into a hot spring, Yellowstone is certainly open for business.

4) No volcanologists have stated that Yellowstone is likely to erupt this week, this month or this year. In one recent article, a name was attributed to a "senior volcanologist", but that person does not appear to exist, and a geologist with that name assures us that he did not supply any quotes regarding Yellowstone.

5) Finally, we note that those who've kept track of Yellowstone over the past decade or so, have seen a constant stream of "predictions" regarding imminent eruptions at Yellowstone. Many have had specific dates in mind, none had a scientific basis, and none have come true.

We will continue to provide updates on geological activity at Yellowstone, and educational materials to help understand the science around Yellowstone monitoring.

Virtually everything known about Yellowstone's spectacular volcanic past comes from the scientists who work at this observatory, at all our eight member agencies. We're the ones who mapped the deposits, figured out the ages of the eruptions, measured the gases, located the earthquakes, and tracked the ground movement. A few of us have been doing it for over forty years. We will continue to help you understand what's happening at Yellowstone now, and what's likely to happen in the future.

How do we know what's beneath Yellowstone, and how can we image the shallow magma? Seismologists at the University of Utah (a YVO member agency) and the Swiss Federal Institute of Technology undertook a study to image the Yellowstone magma reservoir through a technique called seismic tomography. Using improved methods and data from thousands of earthquakes; they discovered that the magma reservoir is much larger than inferred in previous studies. Read our website article to find out how the study was conducted and what they discovered. The complete results from this new approach are published in the Journal Geophysical Research Letters.

Scientists from the University of Utah – a YVO partner agency – recently presented new research at the Fall meeting of the American Geophysical Union in San Francisco that suggests that the size of the magma body beneath Yellowstone is significantly larger than had been thought. Previous similar studies had underestimated the size of the magma body because of insufficient instrumentation. Over the past decade, improvements to the Yellowstone monitoring network has increased the number and quality of the instruments deployed. This new research takes advantage of these upgrades, which will continue to pay dividends for years to come.

The UU researchers, in collaboration with a scientist from the Swiss Seismological Service in Zurich, used a method called seismic tomography to create an improved image of the magmatic system beneath Yellowstone. One should not think of Yellowstone's magma reservoir as a big cavern full of churning lava. Rather, the reservoir is distributed throughout a porous, sponge-like body of otherwise solid rock, with the amount of liquid rock (melt) varying from place to place. Because seismic waves slow down when traveling through liquids, seismic tomography can be used to map out these variations. The new research shows that while the magma reservoir is bigger than we thought, the proportion of melt to solid rock (estimated at <10-15%) is similar to previous reports and appears to remain way too low for a giant eruption.

Although fascinating, the new findings do not imply increased geologic hazards at Yellowstone, and certainly do not increase the chances of a "supereruption" in the near future. Contrary to some media reports, Yellowstone is not "overdue" for a supereruption. Indeed, it is quite possible that such an eruption will never again occur from the Yellowstone region. Scientist agree that smaller eruptions are likely in the future, but the probability of ANY sort of eruption at Yellowstone still remains very low over the next 10 to 100 years.

YVO scientists from organizations around the country continually monitor geologic conditions at Yellowstone. At present those conditions are normal and there is no heightened concern for public safety. Should conditions change, an established alert system will quickly notify public officials, the general public, and the media. YVO posts regular updates about activity at Yellowstone, which can be found on the activity update webpage. We encourage you to explore our website for additional information on geologic hazards and current activity at Yellowstone.

The YVO webcam is offline temporarily. We hope to get it up and running soon. Please be aware that the camera runs via a solar panel and cellular modem. Unlike most similar cameras, it does not have connection to either AC power or the internet. In the interim, here's a nice image from the camera taken the last week that the camera was operational.

• Monitoring data is displayed as an interactive map
• Webcam images are located in Multimedia and on the monitoring map
• Hazards information is more detailed
• Frequently Asked Questions are organized by category
• Image Galleries are added for easy image browsing

• What geological units will my hike pass through?
• How many earthquakes have occurred at Yellowstone so far this year?
• Was the latest earthquake located near the caldera boundary?
• Where are thermal areas found in the Central Plateau?
• Where does high resolution topographic data (LiDAR) exist at Yellowstone?
• What is the closest seismometer to my hotel/home/campsite?

USGS scientist Phil Dawson and colleagues have applied a novel research approach to voice recognition software. In their January 2012 paper, published in Geophysical Research Letters, they utilize this software to discover that background seismic activity in geyser basins can be intimately linked to daily cycles of heating and cooling. For more information read the web article in the Yellowstone volcano earthquake monitoring section.

Recent telemetry problems, from ice and snow buildup on data transmission antennas, have caused intermittent malfunctions of the University of Utah's automated earthquake location system. The malfunctions result in false earthquake reports, which upon review, are then manually deleted from the earthquake catalog. The snow and ice buildup interferes with the continuous streaming of seismic data causing occasional signal dropouts. The dropouts cause spikes to appear in the data streams, which the automated system misinterprets as the abrupt appearance of a high amplitude seismic wave from an earthquake. Windy conditions, common this time of year, exacerbate the problem by contributing additional noise and thereby reducing the overall signal quality of the seismic data streams. In most cases, seismologists at the University of Utah can overcome these problems and still identify and locate earthquakes correctly. Seismic activity at Yellowstone remains at background levels.

By checking the webicorder displays one can easily discern whether an actual earthquake has occurred. Please see this tutorial for how to interpret the webicorders.

More information about errors in the real-time earthquake system that lead to erroneous reports can be found here: Earthquake Hazards Program Errata for Real-time Earthquakes page.

Beginning October 1, 2010, the University of Utah Seismograph Stations has reduced the threshold from M 2.5 to M 1.5 for automated plotting of earthquakes for the Yellowstone region. For more information please see the UUSS announcement. See today's earthquake map.

A report, "Protocols for Geologic Hazards Response by the Yellowstone Volcano Observatory," has just been published. The document summarizes the protocols and tools that the Yellowstone Volcano Observatory (YVO) will now use during earthquakes, hydrothermal explosions, or other geological activity that could lead to a volcanic eruption. This USGS circular was written by an inter-organizational group of scientists, land managers, and emergency responders that met in November 2008 in Bozeman, Montana.

YVO has finished installing a series of radio-equipped temperature sensors to document changes in water flow and heat discharge in the Norris Geyser Basin. Daily, weekly, and monthly temperature plots are now available from our new monitoring page, "Taking the Temperature of the Norris Geyser Basin."

Geysers are rare hot springs that periodically erupt bursts of steam and hot water. Yellowstone National Park has more than half of the world's geysers. Old Faithful has remained faithful for at least the past 135 years, showering appreciative tourists every 50 to 95 minutes (most recently an annual average of 91 minutes). To view Old Faithful in real-time, see the National Park Service Old Faithful Webcam.

There were were notable changes in thermal activity at Norris Geyser Basin in 2003. These changes resulted in the closure of the Back Basin Trail and temporarydeployment of a monitoring network by YVO. Learn more.