Title: Long Valley Caldera 2003 through 2012: Overview of low level unrest in the last decade Authors: Stuart Wilkinson, David Hill, Michael Lisowski, Deborah Bergfeld, Margaret Mangan
Abstract
Long Valley Caldera is located in central California along the eastern escarpment of the Sierra Nevada and at the western edge of the Basin and Range. The caldera formed 0.76 Ma ago during the eruption of 600 cubic kilometers the Bishop Tuff that resulted in the collapse of the partially evacuated magma chamber. Since at least late 1978, Long Valley Caldera has experienced recurring earthquake swarms and ground uplift, suggesting future eruptions are possible. Unrest in Long Valley Caldera during the 1980s to early 2000s is well documented in the literature. Episodes of inflation centered on the resurgent dome in the western part of the caldera occurred in 1979-1980, 1983, 1989-1990, 1997-1998, and 2002-2003, accumulating ~ 80 cm of uplift. Earthquakes of M ≥ 3.0 were numerous in the caldera and in the Sierra Nevada block to the south of the caldera from 1980 through 1983 (800 events including four M~ 6 earthquakes in 1980); in the caldera from 1997 through mid-1998 (150 events); and in the Sierra Nevada block from mid-1998 through 1999 (~160 events) and more modestly from 2002 through 2003 (7 events). In this presentation, we summarize the low-levels of caldera unrest during the last decade. The number of earthquakes in Sierra Nevada block and the caldera has gradually diminished over the last decade. Fifty Sierra Nevada earthquakes had magnitudes 3.0≤M≤4.6. In the caldera, only six earthquakes had magnitudes 3.0≤M≤3.8. A three-month swarm of minor earthquakes (235 events with 0.5≤M≤3.8; most below 2.0) occurred in the caldera in mid-2010. Analysis of continuous GPS data over the last year shows an inflationary pattern within the caldera centered on the resurgent dome, with a maximum uplift rate of ~ 2-3 cm/yr. The rate of deformation is comparable to that of 2002-2003, and well below ~ 70 cm/yr rates observed during the peak of inflation in the late 1990s. Steaming ground and diffuse CO2 discharge has long been a feature of Long Valley Caldera, especially on or around the resurgent dome, where the anomaly is readily seen by stressed and dying vegetation. Measurements at 13 locations from 2003-2004 show emission of ~8.7 CO2 t/d over ~30 acres with shallow soil temperatures as high as 90°C. Surveys conducted from 2006 to 2010 at the two main disturbed zones suggest release of 6-11 t/d over 15 acres with temperatures as high as 75°C, and 3-5 t/d over ~4 acres and a 93°C maximum temperature. The highest discharges of heat and gas are located within a few kilometers of the Casa Diablo geothermal plant. Over the past 30 years LVC has experienced intense periods of inflation of the resurgent dome and produced multiple sequences of strong earthquakes. While unrest in recent years has been less than the previous decade, the potential for renewed volcanism persists, making ongoing monitoring essential.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.V31B2780W
- Keywords:
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- 8419 VOLCANOLOGY / Volcano monitoring;
- 8430 VOLCANOLOGY / Volcanic gases;
- 8440 VOLCANOLOGY / Calderas;
- 8488 VOLCANOLOGY / Volcanic hazards and risks