Probing the Depths of Long Valley Caldera
August 15, 2018
A new study by CalVO seismologists used a novel geophysical technique called "full waveform seismic tomography" to image the roots of Long Valley Caldera in eastern California. The study revealed a zone of low seismic wave velocity >1000 cubic kilometers in volume, of which, an average of 27% may be molten. This partially-molten zone is deep within the crust, below about 10 kilometers, and only small pockets of it may be fluid enough to rise upwards and eventually erupt. Although eruptions as large as the one that produced Long Valley Caldera 767,000 years ago are extremely rare, understanding the volume of melt in the roots of volcanic areas is critical for understanding the potential for future eruptions and for anticipating the hazards that may ensue.
[Ashton F. Flinders, David R. Shelly, Philip B. Dawson, David P. Hill, Barbara Tripoli, and Yang Shen; https://doi.org/10.1130/G45094.1
Pleistocene volcanism and shifting shorelines at Lake Tahoe, California
April 18, 2018
A recently-published study
co-authored by two CalVO scientists brings attention to the role that lava dams played in shaping Lake Tahoe. New radiometric argon ages have revealed that between 2.3 and 0.94 million years ago, a small volcanic field in the northwestern Lake Tahoe basin produced basaltic lava flows that dammed the lake three separate times. These 'lava dams' raised the lake level level dozens to hundreds of feet and created raised shorelines. In addition, deltas of brecciated (fragmented) lava, pillow basalts, and tuff cones were formed where lava flows entered the lake - deltas and tuff cones when it reacted explosively with the water, and pillow basalts when the entry was less violent.
The repetitive timing of this volcanic activity poses some interesting questions about hazards. The Lake Tahoe area is not currently considered to be volcanically active (it must have had an eruption in the last 10,000 years to meet that criteria). However, if magma were to return to the area, future eruptions and new lava dams would pose a flooding hazard both around the Lake Tahoe basin and beyond. Lava dams are known to fail rapidly, and a dam that raised the level of the lake and then collapsed could cause serious flooding downstream along the Truckee River. For now, however, there is no danger of an eruption, and such an event might be hundreds of thousands or even millions of years in the future - or might never occur at all.
Kortemeirer, W., Calvert, A., Moore, J.G., Schweickert, R., 2018, Pleistocene volcanism and shifting shorelines at Lake Tahoe, California: Geosphere, vol. 14, no. 2, 23 p. doi: 10.1130/GES01551.1.
USGS volcanologists conduct volcanic crisis training in Chester, CA
December 18, 2017
It isn't often that scientists and land managers spend two entire days together talking about volcanoes outside of an eruptive crisis, but a special FEMA training course allows them to do just that. In mid-November, Margaret Mangan and Jessica Ball of CalVO, John Ewert of CVO and Jeff Rubin of Tualatin Valley Fire and Rescue led local emergency managers, fire responders, law enforcement officers, and National Park staff in a FEMA Volcanic Crisis Awareness
training held in Chester, CA (near Lassen Volcanic National Park).
The course is designed to give a primer on volcanic hazards and how the USGS monitors volcanoes and communicates in a crisis, but also devotes ample time to a tabletop eruption scenario where emergency managers are led through a fictional volcanic crisis and discuss how they would respond to escalating volcanic activity. The two-day course addresses the scientific, communication, managerial, and psychological aspects of volcanic crises, and allows insight into the goals of different groups in responding to volcanic hazards. CalVO scientists will conduct a similar training at Lassen Volcanic National Park in January 2018.
Explore California's volcanic legacy and future with new field trip guides
July 05, 2017
California is well-known for its frequent earthquakes, but less so for its volcanic history – despite the fact that the most recent eruption in the state occurred just 100 years ago. Nearly every kind of volcanic landform is represented in California, from the stratocone of Mount Shasta to the lava domes of the Mono-Inyo Craters to the steam explosion features of Ubehebe Craters. To explore this wealth of geologic phenomena, use some of the USGS's newly published and upcoming volcanic field trip guides!
Several new and updated field guides for the 2017 Scientific Assembly of the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) in Portland, Oregon showcase California's volcanoes. Upcoming publications for Medicine Lake, Mount Shasta, Lassen Peak, Long Valley and Mammoth Mountain will provide easy to follow and informative field trips. The new collection of guidebooks can be found at the USGS Publications Warehouse and summarizes decades of advances in understanding volcanic and tectonic processes of western North America.