The seismic activity that started on the evening of July 5 at the southern margin of Coso Volcanic Field in Inyo County, California continues at a rate of about 600 M1.0 or greater earthquakes per day. The activity was triggered by a magnitude M5.4 earthquake at 9:19 PM PDT located 20 km (~20 miles) ESE of Little Lake, which itself was an aftershock of the M7.1 earthquake that occurred about an hour earlier on the 5th, located 17 km NNE of Ridgecrest to the south. The intensity of the activity at Coso is gradually declining. Of the approximately 1600 earthquakes detected at M1.0 or above since July 8, only 12 have been M3.0 or above, with the largest two registering M4.1.
The current activity at Coso can be considered distant aftershocks, or triggered earthquakes. The M7.1 on July 5 occurred on a NW-trending fault oriented toward the Coso area, and it is common for large earthquakes to cause aftershocks beyond the actual fault rupture. No ground deformation indicative of volcanic activity has been detected, and there is no imminent threat of an eruption. The California Volcano Observatory will continue to monitor the situation for any sign of volcanic activity and provide updates as warranted.
In addition to studying volcanic processes and their associated hazards in California and Nevada, scientists at the California Volcano Observatory also collaborate with other volcano observatories to work on volcanic processes throughout the United States. One collaboration is looking at the timing and frequency of volcanism associated with Yellowstone Caldera, located within Yellowstone National Park.
Yellowstone Caldera is famous for a super-eruption ~631,000 years ago that ejected 240 mi3 of material, but these catastrophic events only represent a small fraction of the system's 2.1-million-year eruptive history. More commonly, Yellowstone produces smaller rhyolite lava flows with volumes ranging from 0.1 mi3 to 17 mi3, although these eruptions are still quite large (for comparison, Mount St. Helens in 1980 erupted ~0.06 mi3 of material). In the last 631,000 years, at least 28 rhyolite eruptions have occurred within Yellowstone Caldera. However, it is unknown whether these eruptions occurred steadily over this timeframe or whether multiple eruptions clustered over short time intervals. This information is important for understanding volcanic hazards posed by Yellowstone's magmatic system, because if eruptions are clustered in time then the occurrence of one eruption may indicate that the next eruption may follow closely.
Currently, research is underway at Yellowstone to quantify the frequency of these smaller rhyolite eruptions. To do this, USGS scientists are measuring the age of volcanic rocks using a technique called 40Ar/39Ar dating, which is based on the timing of radioactive decay of potassium to argon. Preliminary results suggest that these smaller rhyolite eruptions were highly clustered in time, erupting in discrete episodes. During one of these eruptive episodes, up to 7 different eruptions occurred within the caldera over period of a thousand years or less. As research continues, scientists hope to refine the estimates of how long these eruptive episodes lasted, and incorporate those estimates into volcanic hazard assessments for Yellowstone.
Scientists at the volcano observatories of the U.S. Geological Survey pay close attention to volcanoes of the Cascade Range, Alaskan Peninsula and Aleutian Arc. These areas have young and frequent volcanic eruptions, form conspicuous large edifices, and can produce high-silica magmas that are sometimes very explosive. These volcanoes threaten life and property, even including jet aircraft that might fly over them.
A different group of volcanoes are located to the east of the Cascade Range from northern California to central Oregon. In this region, the extensional tectonics of the Basin-and-Range province impinge on the subduction process that created the Cascade Range. These "rear-arc" volcanoes are not explosive, but instead erupt fluid magmas, akin to Hawaiian basalts, at intervals of 10s to 100s of thousands of years. Their high effusion rates produce eruptions that can inundate scores of km2 in just months to years with volumes 6 to 8 km3of lava. The broad lava flow fields from these eruptions are gently inclined, and fill the topographic basins between older, eroded volcanoes. Through time, the basins are covered by sediments, and form marshy, and grassy meadows in the dry environments of northern California and central Oregon. Because the basalt lava in these flows shrinks upon cooling and forms cracks, they hold and convey groundwater from zones of higher rainfall to areas that are semi-arid. This abundant groundwater resource is very important to the economy of NE California and central Oregon.
Scientists at the California Volcano Observatory are studying an interesting aspect of 3 of these voluminous rear-arc basalt eruptions around 300,000 years ago. While rear-arc eruptions are usually separated in time, these 3 eruptions share nearly identical whole-rock chemistry values, and have identical characteristic remanent magnetic directions, "locked in" when they erupted and cooled. This suggests that all 3 eruptions occurred in no more than a century or two. Vents for the Tennant and Dry Lake basalt fields are only 9 km apart, separated by a ridge of older volcanic rocks, whereas the vent for the Hammond Crossing basalt field is farther SSE and 56 km from the Dry Lake vent. The dike(s) that fed the common eruptive episode which created these lava fields may have been very long, breaking the surface at very separate locations. The study's authors are examining other, older voluminous rear-arc lava fields to see if additional, common eruptive episodes can be identified.
The Mono Craters, a line of volcanic domes and craters south of Mono Lake in eastern California, represent the youngest rhyolitic volcanoes in the western United States. Rhyolite is a magma that is viscous and prone to explosive eruption. Consequently, these volcanoes pose a significant volcanic hazard to the region. Volcanic ash from past eruptions of Mono Craters covered large areas of California, and fell as far as Utah and Nevada. Up to now, the chronology of volcanism at Mono Craters has only been partly understood. The timing of the youngest eruptions has been known from carbon-14 dating of plants that were buried by ash; however, the chronology of the older eruptions has been uncertain.
A new study using tiny mineral crystals and the radioactive-decay series of uranium has revealed the early eruption history of Mono Craters. Marcaida et al. (2019) used an ion-shooting mass spectrometer to measure uranium and its daughter isotopes in zircon and allanite crystals in the rhyolites, and calculated the ages of their crystallization immediately before eruption. The results reveal that about 20 eruptions occurred between 10,000 and 65,000 years ago. In addition, the researchers used the new data to correlate ash beds around Mono Lake to their source volcanoes, and were able to identify ash expelled by explosive eruptions at nearby Mammoth Mountain.
Marcaida et al., 2019, Constraining the early eruptive history of the Mono Craters rhyolites, California, based on 238U–230Th isochron dating of their explosive and effusive products: Geochemistry, Geophysics, Geosystems. https://doi.org/10.1029/2018GC008052
The potential for damaging earthquakes, landslides, floods, tsunamis, and wildfires is widely recognized in California. The same cannot be said for volcanic hazards, despite the fact that eruptions occur in the state about as frequently as the largest earthquakes on the San Andreas Fault in San Francisco. At least ten volcanic eruptions have taken place in California in the past 1,000 years—most recent is the Lassen Peak eruption of 1914 to 1917 in Northern California—and future volcanic eruptions are inevitable. Based on the record of volcanism over the last few millennia, the likelihood of another eruption occurring in California in the next 30 years is about 16 percent.
A new 2019 report, "California's Exposure to Volcanic Hazards", prepared in collaboration with the State of California Governor's Office of Emergency Services (CalOES) and the California Geological Survey (CGS), provides a broad perspective on the State's exposure to volcanic hazards by integrating volcanic hazard information with geospatial data on at-risk populations, infrastructure, and resources. The information in this report is intended to prompt follow-up site and sector specific vulnerability analysis and improved hazard mitigation, disaster planning, and response protocols.
Read the report here: https://pubs.er.usgs.gov/publication/sir20185159
A new USGS report, Science for a Risky World: A USGS Plan for Risk Research and Applications, defines for the first time the role of USGS in risk research and applications. This includes hazard assessments, operational forecasts and warnings, vulnerability assessments, risk assessments, risk communication, decision-support systems, and post-event assessments. These activities and products are connected by the need to directly support decision makers in their efforts to better understand societal risk from hazards and to have the necessary information to make science-based, risk reduction decisions. The Risk Plan identifies the Bureau's core competencies in this arena and includes background on and specific recommendations for building institutional capacity for creating sustained partnerships, supporting professional staff, and improving product delivery.