California Volcano Observatory

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Date published: September 28, 2014

Earthquake Swarm in Long Valley Caldera Diminishes

Over the past 42 hours, the earthquake swarm in California's Long Valley Caldera, which began last Friday (see September 26 post), has gradually diminished in terms of numbers of earthquakes and in earthquake magnitude.

Date published: September 26, 2014

Earthquake Swarm in Long Valley Caldera

We have been closely tracking an earthquake swarm in California's Long Valley Caldera, which started yesterday at around 4AM PDT (September 25, 2014).

Date published: September 25, 2014

Mount Shasta debris flow not linked to volcanic activity

On the afternoon of September 20, a large volume of water surged down Mount Shasta's south flank into Mud Creek, entraining debris and inundating the drainage and roads near McCloud, California.

Date published: August 12, 2014

Automated Volcanic-Gas Sniffer Installed at Mammoth Mountain Fumarole

In July 2014, USGS Scientists Peter Kelly (Cascades Volcano Observatory) and Stuart Wilkinson (California Volcano Observatory) installed an automated volcanic-gas monitoring station on Mammoth Mountain, located on the SW rim of Long Valley Caldera (CA).

Date published: July 3, 2014

Investigating Past Eruptions of Mono Craters

CalVO geologist Mae Marcaida examines thin layers of volcanic ash sandwiched between thick beds of sediment deposited by ancestral Mono Lake in eastern California.

Date published: June 27, 2014

Small Earthquake Swarm

A swarm of small earthquakes (magnitudes less than 2) occurred at a depth of 6-7 km (about 4 miles) beneath Highway 203 in Mammoth Lakes, California midway between the water treatment plant and the Highway 395-203 junction, June 27, 2014.

Date published: February 18, 2014

Earthquake swarm under Mammoth Mountain - Update

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.

Date published: February 6, 2014

Earthquake swarm under Mammoth Mountain

An earthquake swarm under Mammoth Mountain (Mono County, CA), which started slowly on February 3, 2014 intensified in the early hours of February 5 with many small-magnitude earthquakes occurring in rapid succession, a phenomenon known as "spasmodic bursts."

Date published: October 29, 2013

Volcano Hazard Mitigation Included in California Multi-hazard Mitigation Plan

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.

Date published: October 21, 2013

Magnitude 3.8 earthquake in Long Valley region is tectonic, and not volcanic, in origin

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.

Date published: July 2, 2013

Instrumentation Installed for Continuous Monitoring of Carbon Dioxide Emissions at Horseshoe Lake, Mammoth Mountain

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.

Date published: June 18, 2013

Small Swarm in Long Valley 17 June 2013

In the late afternoon of 17 June 2013 a flurry of earthquakes started in the Long Valley Caldera east of the town of Mammoth Lakes, California (in an area known to geologists as the south moat).