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Cascade Range Weekly Update
Friday, September 15, 2017 1:36 PM US/Pacific
Current Volcano Alert Level: NORMAL
Current Aviation Color Code: GREEN
Cascades Volcano Observatory's mission
The U.S. Geological Survey's Cascades Volcano Observatory strives to serve the national interest by helping people to live knowledgeably and safely with volcanoes in WA, OR, and ID.

HOT STUFF   (archive)
Young Volcanoes in WA, OR & ID1

Seismologists deploy largest number of seismometers ever at Mount St. Helens—a dense array designed to detect tiny quakes.
August 30, 2017

Between August 19 and 22, seismologists with the USGS-Cascades Volcano Observatory, University of New Mexico, University of Oregon, University of Wisconsin-Madison, Cornell and Northwestern worked together to install 140 temporary seismometers at Mount St. Helens. Instruments were placed on top of the lava dome that erupted in 2004-2008, as well as the 1980-86 lava dome, the 1980 crater floor, and around the volcanic cone. The goal of the month-long deployment is to capture small magnitude volcanic earthquakes and learn more about the shallow plumbing system beneath the crater floor.

The project represents the largest number of seismometers ever placed on a U.S. volcano. The seismometers, which resemble an insulated big-mouth thermos with spikes on the bottom, weigh only six pounds, are self-contained, and are easy to deploy. The seismometers store data on a small internal computer and have enough battery power to operate for about one month.

"The goals of the project are to more precisely locate and characterize the small-magnitude volcanic earthquakes that routinely occur at St. Helens. We also want to be able to more reliably discriminate volcanic earthquakes from rockfalls off the crater wall, which have a similar seismic signature in many cases," said Wes Thelen, a seismologist with the USGS-Cascades Volcano Observatory. "Once we collect the data and have a better idea about what is occurring in the shallow subsurface, we will be able to compare those signals with signals recorded on our permanent network stations to recognize and identify earthquake sources when they happen again."

The data will augment the results of the recently completed iMUSH (imaging Magma Under St. Helens) experiment. The equipment used in iMUSH looked "deeper" than a mile (2 km), whereas this project looks at shallow earthquakes that occur between the surface and 2 km. A number of earthquakes and rockfalls have already occurred since the instruments were deployed.

Mount St. Helens is the most seismically active volcano in the Washington and Oregon Cascades. In an average month about 20 events are located by the Pacific Northwest Seismic Network, with the number going far higher during eruptive periods. Seismologists have also tracked several shallow earthquake swarms at Mount St. Helens since the eruption ended in 2008, most recently in May of 2017. Generally, swarms consist of tens to hundreds of earthquakes with magnitudes less than M1.5 and depths between 1 and 4 miles (2 to 7 kilometers) below the surface. These swarms are believed to be associated with the ongoing magma recharge of the plumbing system beneath Mount St. Helens, but are not an indication that an eruption is imminent.

Crews will return to Mount St. Helens on September 20-22 to retrieve the equipment and collect the data. Use this link to learn more about Monitoring Instruments and Data at Mount St. Helens.

Mount St. Helens field guide provides insight into the Cascade Range's most active volcano over the past 4000 years.
August 30, 2017

Mount St. Helens has been referred to as a "master teacher." The 1980 eruption and studies both before and after 1980 played a major role in the establishment of the modern USGS Volcano Hazards Program and our understanding of flank collapses, debris avalanches, cryptodomes, blasts, pyroclastic density currents, and lahars, as well as the dynamics of magma ascent and eruption.

The guide, Field-Trip Guide to Mount St. Helens, Washington—An Overview of the Eruptive History and Petrology, Tephra Deposits, 1980 Pyroclastic Density Current Deposits, and the Crater, provides an overview of the eruptive history of Mount St. Helens, and the volcanologic and petrologic insights resulting from studies of the 1980-86 and 2004-2008 lava domes. The guide describes the dynamics and progressive emplacement of pyroclastic flows, classic tephra outcrops of the past 3,900 years and how the petrology and geochemistry of Mount St. Helens deposits reveal the evolution of the magmatic system through time.

The field guide was developed for the August 2017 International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Scientific Assembly in Portland, Oregon.

Field guide tracks flood basalts, rhyolites and post-plume volcanism in eastern Oregon.
August 29, 2017

The Miocene Columbia River Basalt Group (CRBG) is the youngest and best preserved continental flood basalt province on Earth. It is linked in space and time with a compositionally diverse succession of volcanic rocks that partially record the apparent emergence and passage of the Yellowstone plume head through eastern Oregon. This compositionally diverse suite of volcanic rocks are considered part of the La Grande-Owyhee eruptive axis (LOEA), an approximately 185 mile-long volcanic belt located along the eastern margin of the Columbia River flood basalt province. Volcanic rocks erupted from and preserved within the LOEA form an important regional stratigraphic link between the (1) flood basalt-dominated Columbia Plateau on the north, (2) bimodal basalt-rhyolite vent complexes of the Owyhee Plateau on the south, (3) bimodal basalt-rhyolite and time-transgressive rhyolitic volcanic fields of the Snake River Plain-Yellowstone Plateau, and (4) the High Lava Plains of central Oregon.

The guide, Field-trip guide to Columbia River flood basalts, associated rhyolites, and diverse post-plume volcanism in eastern Oregon, describes a 4-day geologic excursion that will explore the stratigraphic and geochemical relationships among mafic rocks of the Columbia River Basalt Group and the compositionally diverse volcanic rocks associated with the early "Yellowstone track" and High Lava Plains in eastern Oregon.

The field guide was developed for the August 2017 International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Scientific Assembly in Portland, Oregon.

Central Oregon field trip examines the influence of volcanoes and their eruptive products on rivers, groundwater, forests and people.
August 29, 2017

The crest of the Oregon Cascade Range has an average elevation of 5,000 to 6,500 ft, with several of the highest volcanoes exceeding 9,000 ft. The volcanoes intercept moisture from the Pacific Ocean, which falls as rain or snow on the west side of the crest. But to the east, the Cascades create a rain shadow—one of the strongest precipitation gradients in the lower 48 states. Forests east of the crest are a mix of alpine and subalpine hemlocks and firs that transition abruptly into a more open forest of ponderosa pine and lodgepole pine in response to the abrupt decline in rainfall.

Although the focus of this multidisciplinary field trip is on mafic volcanism, it also looks at hydrology, geomorphology, and ecology, and how these elements both influence and are influenced by mafic volcanism. The trip includes travel up the valley of the McKenzie River, the mafic volcanic rocks at the Sand Mountain volcanic field and in the Santiam Pass area, at McKenzie Pass, and in the southern Bend region. Download the Field-trip guide to mafic volcanism of the Cascade Range in Central Oregon—A volcanic, tectonic, hydrologic, and geomorphic journey, for a 6-day trip to central Oregon.

The field guide was developed for the August 2017 International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Scientific Assembly in Portland, Oregon.

Explore the geologic deposits in Crater Lake National Park with this new field guide.
August 28, 2017

Mount Mazama rose to an elevation of over 12,000 ft before its collapse during a rapid series of explosive eruptions about 7,700 years ago. The climactic eruption devastated the terrain for tens of miles, sent pyroclastic flows into every drainage, and produced ash fall throughout much of the Pacific Northwest. Since that eruption, volcanism has been confined within the caldera and most of the volcanic products are hidden from view beneath Crater Lake.

This field guide takes you to locations both inside and outside Crater Lake National Park, where you can see superb exposures of lava flows and pyroclastic deposits, with accompanying descriptions that give exceptional insight into how large volcanoes of magmatic arcs grow and evolve. Follow the driving instructions in the Geologic field trip guide to Mount Mazama and Crater Lake Caldera, Oregon, during your next visit.

The field guide was developed for the August 2017 International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Scientific Assembly in Portland, Oregon.

Field trip examines world-class and historically important volcanic features in the Pacific Northwest.
August 28, 2017

The Pacific Northwest is host to an incredible volcanic landscape. This 4-day field trip guide gives a broad overview of the region's diverse volcanism, focusing on Columbia River Basalts, High Lava Plains, and Cascade Range volcanic features.

The trip begins with an examination of lava flow structures of the Columbia River Basalt—enormous lava fields that were emplaced during one of the largest eruptive episodes in Earth's recent history. On the second day, the trip turns to the High Lava Plains, a bimodal volcanic province that provides excellent examples of welded ignimbrite, silicic lavas and domes, monogenetic basaltic lava fields, and hydrovolcanic features. The third day is devoted to a circumnavigation of Crater Lake, the result of caldera-forming eruptions of Mount Mazama. The last day is spent at Newberry Volcano, a shield volcano topped by a caldera. Newberry is compositionally bimodal with an abundance of explosive and effusive deposits, including the youngest rhyolites in the Pacific Northwest. Download the complete guide, Field-Trip Guide to a Volcanic Transect of the Pacific Northwest, to begin the adventure.

The field guide was developed for the August 2017 International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Scientific Assembly in Portland, Oregon.

Follow the trail of Newberry Volcano lavas with this new field guide.
August 28, 2017

Newberry Volcano is a massive, shield-shaped, composite volcano in central Oregon. Eruptions began about half a million years ago and built a broad edifice that has generated more than one caldera collapse. About 75,000 years ago, a major explosive eruption and collapse event created a large volcanic depression at its summit that now hosts two caldera lakes—Paulina and East Lakes.

A significant mafic eruptive event occurred about 7,000 years ago along the northwest rift zone. This event produced lavas ranging in composition from basalt to andesite, some of which traveled over 20 mi to Lava Butte, to temporarily block the Deschutes River.

The Field-Trip Guide to the Geologic Highlights of Newberry Volcano, Oregon, takes the visitor to a variety of easily accessible geologic sites in Newberry National Volcanic Monument, including the young, spectacular flows of rhyolitic obsidian. Side trips include a visit to the Lava Cast Forest, Lava River Cave, Lava Butte, Benham Falls, Pilot Butte and the Peter Skene Ogden Scenic Wayside, with annotated images and descriptions that offer an overview of the geologic story of Newberry Volcano.

The field guide was developed for the August 2017 International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Scientific Assembly in Portland, Oregon.

Field trip guide examines obsidian-rich lava flows in Oregon and California.
July 24, 2017

Obsidian-rich lava flows have been of interest to geologists, archaeologists, pumice miners, and rock hounds for more than a century. But active rhyolitic obsidian lava flows have never been scientifically witnessed and lively debate ensues at outcrops over the formation of some lava flow features.

At first glance, the surface of an obsidian flow appears to be a chaotic mixture of blocks, spines and hillocks of different colors, sizes, densities, crystallinity and vesicularity. However, on aerial photos (or after one stumbles around for a few hours), patterns begin to emerge. Folds and ridges are caused by flow-parallel compression. Three main textures appear on the flow front—finely vesicular pumice carapace, dense obsidian and coarsely vesicular pumice.

This new field guide takes you to locations at Newberry, South Sister and Medicine Lake Volcanoes, to examine the textural and structural characteristics of silicic lava flows. Download Emplacement of Holocene silicic lava flows and domes at Newberry, South Sister, and Medicine Lake volcanoes, California and Oregon for your next journey to central Oregon and northern California.

The field guide was developed for the August 2017 International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Scientific Assembly in Portland, Oregon.

New field guide explores pyroclastic density current deposits from the May 18, 1980, eruption of Mount St. Helens.
July 07, 2017

On the afternoon of May 18, 1980, pyroclastic density currents (PDCs) spilled over the crater rim and poured through the breach created in Mount St. Helens' north flank. At times, the PDCs collided, scoured and filled channels, laid down beds 40 feet (12 m) thick and traveled as much as 5 miles (8 km) from the vent.

Our ability to interpret the deposits is critical for understanding transport and depositional processes that control PDC dynamics—one of the most dangerous phenomena associated with explosive volcanism. The results of extensive work on the May 18, 1980, PDC deposits show that slope and irregular topography strongly influence PDC flow path, dynamics, criticality (for example, supercritical versus subcritical), carrying capacity, and erosive capacity. However, the influence of these conditions on ultimate flow runout and damage potential warrants further exploration through the combination of field, experimental, and numerical approaches.

This field guide describes the PDC deposits at Mount St. Helens and poses questions for further research. Download Field-trip guide for exploring pyroclastic density current deposits from the May 18, 1980, eruption of Mount St. Helens, Washington to learn more.

The field guide was developed for the August 2017 International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Scientific Assembly in Portland, Oregon.

Field trip guide examines Ohanapecosh and Wildcat Creek deposits near Mount Rainier.
June 29, 2017

Partly situated in Mount Rainier National Park, this field trip guide visits exceptional examples of volcaniclastic successions laid down in continental basins adjacent to the ancestral Cascades arc. The Ohanapecosh Formation (32–26 Ma) and the Wildcat Creek (27 Ma) beds record similar sedimentation processes from various volcanic sources. They show evidence of probable Surtseyan eruptions, tephra fallout over water, entrance of pyroclastic flows into water, scoria-cone building eruptions in shallow water, and resedimentation events. The field trip examines outcrops along White Pass, Cayuse Pass, Chinook Pass and at Burnt Mountain.

Download Field-Trip Guide to Subaqueous Volcaniclastic Facies in the Ancestral Cascades Arc in Southern Washington State—The Ohanapecosh Formation and Wildcat Creek Beds for your next road trip to this area.

The field guide was developed for the August 2017 International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Scientific Assembly in Portland, Oregon.

Explore Mount Hood with this new field trip guide.
June 26, 2017

Starting and ending in Portland, Oregon, this new field trip guide describes stops of geologic interest for a 175-mile adventure around the Mount Hood volcano.

Mount Hood is a 500,000-year-old composite volcano. Unlike Mount St. Helens, Mount Hood has not produced highly explosive eruptions. Rather, it has erupted andesite and (rarely) low-silica dacite lava flows and domes that have built the 11,241-feet-tall volcano. Pyroclastic flows triggered by the collapse of growing lava domes have generated lahars that swiftly melted snow and ice, as well as lahars generated by large landslides, that have surged tens of miles down valleys.

Use this guide to investigate the outcrops and unique features of Mount Hood, learning more about its history and how this active volcano may behave in the future. Download Field-trip guide to Mount Hood, Oregon, highlighting eruptive history and hazards and plan your next visit to the volcano.

The field guide was developed for the August 2017 International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Scientific Assembly in Portland, Oregon.

Seven-day field trip guide tracks the Columbia River Flood Basalts.
June 26, 2017

The Columbia River Basalt Group covers an area of more than 81,000 square miles. As the youngest continental flood-basalt province on Earth (16.7–5.5 Ma), it is well preserved, with a coherent and detailed stratigraphy exposed in the deep canyonlands of eastern Oregon and southeastern Washington.

This new field trip guide begins in southeastern Oregon near Burns, progresses northward into southeastern Washington, continues in the Pasco Basin and ends in the Columbia River Gorge near Stevenson, Washington. The excursions are arranged progressively from the oldest to the youngest units found in the heart of the flood-basalt source region. The road log examines the stratigraphic evolution, eruption history, and structure of the province through a field examination of the lavas, dikes, and pyroclastic rocks of the CRBs.

Download Field-trip guide to the vents, dikes, stratigraphy, and structure of the Columbia River Basalt Group, eastern Oregon and southeastern Washington and plan your summer trip.

The field guide was developed for the August 2017 International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Scientific Assembly in Portland, Oregon.

Deja Vu: Small Earthquake Swarm at Mount St. Helens Does Not Indicate Future Eruptive Activity
May 05, 2017

As many in the Pacific Northwest can attest to, the winter of 2017 has been a rough one.  Deep snow in the high country buried volcano monitoring sites and caused loss of telemetry and/or power. These problems reduced the Mount St. Helens seismic network, operated jointly by the Cascades Volcano Observatory (CVO) and the Pacific Northwest Seismic Network (PNSN), to roughly half its normal operating capacity. The consistently bad weather prevented CVO and PNSN staff from performing any mid-winter repairs.

A clear weather day on April 21, permitted CVO and PNSN personnel to visit Mount St. Helens and restore the seismic network to nearly full capacity. Immediately after repairs were made, the PNSN began locating small earthquakes at relatively high rates (1 earthquake every few hours) under Mount St. Helens. The damage to seismic stations reduced the ability of the seismic network to locate small-magnitude earthquakes, at least somewhat.

Further analysis has revealed that many of the earthquakes look similar to each other, a common feature of swarms at Mount St. Helens and a sign that the events are occurring in close proximity.  Using data from stations operable all winter, CVO scientists used the repeating characteristic of the earthquakes located since April 21 to track down when the swarm started. The result? There is good evidence that the uptick began as early as April 16 and definitely was occurring as of April 18.

As of May 5, the PNSN has located 47 earthquakes near Mount St. Helens since the seismic network was restored on April 21. Utilizing the similarity of earthquakes, we can detect well over 100 earthquakes that are part of this swarm.  Most earthquakes have depths between sea level and 3 mi (5 km) below sea level (approximately 2-7 km below the surface).  This is consistent with depths of earthquakes occurring since 2008, which are thought to be in response to recharge in the magmatic system.  Earthquake rates, though relatively high compared to background, are still only 1 earthquake every few hours, a rate that is consistent with past small swarms since 2008.  All earthquakes are volcano tectonic in character (no detected low-frequency or long period earthquakes) and the maximum magnitude thus far is a M1.3.  There is no detectable deformation or gas signal associated with this swarm.

Similar swarms occurred at Mount St. Helens in March-May 2016 and November 2016.  Both swarms had repeating earthquakes, average rates of 1-2 earthquakes/hour, and most earthquakes with magnitude below M1.5. 

The similarity of swarms at Mount St. Helens leads us to believe that similar processes cause them, and they are likely tied to magma recharge first detected in 2008. However, pinpointing that exact process is difficult. Some possible mechanisms include a spontaneous release of brine from the pressurized magma chamber into the crust above, a pulse of magma into the magma reservoir that transferred stress into the crust above, or just the breakage of a new pathway of fluid flow that was previously blocked by precipitated minerals. There are several reasons why it is very unlikely that this swarm is a precursor to imminent eruptive activity at Mount St. Helens—it is similar to ones in the past that did not lead to surface activity; it consists of very small earthquakes occurring at relatively low rates; there are no other geophysical indicators (deformation, tilt, gas) of unrest.

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