Earthquake swarm under Mammoth Mountain - Update
February 18, 2014
The earthquake swarm under Mammoth Mountain which started on February 3, 2014 has declined over the past few days. The daily numbers of earthquakes, however, are not yet at background levels. Most earthquakes were (are) M1.5 and less. Many are less than 1.0. The largest event detected was a M3.1, which occurred during peak activity on February 5 (event was upgraded from reported M3.0 to M3.1 after further inspection of the data). At 5 AM PST on February 8, a second period of heightened intensity similar to that observed on February 5 started, which persisted for about 1 hour. During the hour of heightened activity on the 8th, four M2.0+ earthquakes occurred, with the largest a M2.4. A few folks on the mountain felt the M2.4. CalVO deformation monitoring sensors on Mammoth Mountain show no significant change. The swarm is likely caused by the migration of deep-seated hydrothermal fluids. The migrating fluid pressurizes and weakens pre-existing faults causing rock to crack, producing earthquakes. Preliminary measurements made last week suggest carbon dioxide emissions at Mammoth Mountain fumarole have not changed notably; additional magmatic gas data await laboratory analysis of samples to be collected by the USGS this week.
Volcano Hazard Mitigation Included in California Multi-hazard Mitigation Plan
October 29, 2013
On October 6, 2013 the California Office of Emergency Services (CalOES) published its 2013 State of California Multi-Hazard Mitigation Plan
complete with a chapter from the USGS on volcano hazard mitigation. This document is the official statement of the State's hazard identification, vulnerability analysis, and hazard mitigation strategy. Volcanic eruptions occur in California about as frequently as the largest San Andreas Fault Zone earthquakes. Our State Geologist, John Parrish states, "California is the most geologically diverse state in the Nation. We are known for our earthquakes, landslides, and flood hazards. But our nearly forgotten hazard is our volcanoes." With as many as ten eruptions in the last 1,000 years, recognizing the potential for renewed volcanism in California is an essential first step in mitigating hazardous impacts.
You can see the full Mitigation Plan
on the CalOES website.
Magnitude 3.8 earthquake in Long Valley region is tectonic, and not volcanic, in origin
October 21, 2013
A magnitude 3.8 earthquake occurred on October 21, 2013 at 10:04 PDT 18 km (11 miles) SE of the town of Mammoth Lakes in eastern California. It was weakly felt by some in Mammoth Lakes, Bishop, and nearby areas. This event occurred in area of persistently high seismicity beneath the Sierra Nevada mountains, and follows magnitude 3.3 and 3.4 events that occurred nearby on October 11. These earthquakes are occurring at a depth of about 8 km (5 miles) beneath the surface, and appear to related to regional tectonic stresses (combination of strike-slip and extensional faulting) rather than volcanic unrest in Long Valley caldera. For more information about the earthquake, visit the event webpage
. Click image to right for mapped location and description.
Instrumentation Installed for Continuous Monitoring of Carbon Dioxide Emissions at Horseshoe Lake, Mammoth Mountain
July 02, 2013
Since 1990, high levels of carbon dioxide (CO2) in the soil have killed trees within about a 75-acre area adjacent to Horseshoe Lake on the south side of Mammoth Mountain. This CO2 migrates upwards to the surface from depth beneath the mountain. In June 2013, a new measurement array was installed by the USGS adjacent to Horseshoe Lake to continuously monitor changes in CO2 emissions over space and time. At the heart of this instrumentation is a set of atmospheric sensors mounted on a tripod tower above the ground surface. These sensors make high-frequency measurements of atmospheric CO2 concentrations and wind speeds and directions. Using the "eddy covariance" method, these measurements are then used to calculate rates of CO2 emission from land areas around the instrument tower (which change with atmospheric conditions such as wind speed and direction) on a half-hourly basis. Continuous monitoring of CO2 emissions should allow for better understanding of the relationships between changes in these emissions and variations in local weather conditions and activity (for example, seismicity) beneath Mammoth Mountain.