Earthquake Swarm in Long Valley Caldera Diminishes
September 28, 2014
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. At present, the rate of seismicity within the caldera is approaching background, with about 5 earthquakes between magnitude M1.0 to M2.8 occurring per hour. The swarm poses no immediate hazard. The USGS California Volcano Observatory will continue to track this activity and provide updates as appropriate.
Earthquake Swarm in Long Valley Caldera
September 26, 2014
We have been closely tracking an earthquake swarm in California's Long Valley Caldera, which started yesterday at around 4AM PDT (September 25, 2014). The swarm is located 7 miles east of the town of Mammoth Lakes, about a mile north of the airport. From about 4 AM on the September 25th to 11AM on September 26th there have been more than 500 earthquakes of magnitude M1.0 and above, including 8 earthquakes between M3.0 and M3.8, which were felt locally. This is one of several earthquake swarms that have occurred in the caldera this year. Despite the several felt earthquakes, this is still rather modest activity compared with the much more energetic swarms occurring in the 1980s and 1990s. We do not see any evidence for anomalous ground deformation associated with the swarm at this time. Part of the Long Valley Caldera, known as the "resurgent dome," has been uplifting at a rate of about an inch per year since late 2011, and this remains unchanged. Caldera uplift has occurred sporadically for the last few decades. The uplift rate observed since 2011 is small compared to rates observed in the 1980s and 1990s. The earthquakes themselves are small, brittle-failure (rock breaking) events. Such events are sometimes called "tectonic." The earthquakes do not result from the underground movement of magma. We can distinguish between brittle-failure earthquakes and those resulting from magma movement by the characteristics of the seismic waveforms.
The swarm events pose no immediate hazard. The USGS California Volcano Observatory will continue to closely track this activity and provide updates as appropriate.
9/20/14 Mount Shasta debris flow not linked to volcanic activity
September 25, 2014
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. USGS seismologists have determined that the event was not triggered by volcanic or seismic activity. There is no visible change to the Konwakiton Glacier at the head of Mud Creek. The USFS reports that the debris flow was triggered either by rapid release of subglacial water or ponded water from the Mount Shasta Summit Plateau.
Automated Volcanic-Gas Sniffer Installed at Mammoth Mountain Fumarole
August 12, 2014
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). The station tracks the temperature and concentrations of carbon dioxide and other gases at a steaming vent high on the north flank of the mountain known as Mammoth Mountain Fumarole. Temperature and gas composition often fluctuate with earthquake activity under the mountain, probably because shaking opens new pathways for heat and gas to flow towards the surface. The new gas monitor will help scientists track these changes in near real-time. The station will be deployed for the summer months and retrieved before deep snow blankets the mountain.
Investigating Past Eruptions of Mono Craters
July 03, 2014
CalVO geologist Mae Marcaida examines thin layers of volcanic ash sandwiched between thick beds of sediment deposited by ancestral Mono Lake in eastern California. Each ash layer is evidence of a past explosive eruption of the Mono Craters, which began erupting about 65,000 years ago just south of present-day Mono Lake. Marcaida and her colleagues use the chemistry of magnetic minerals (titanomagnetites) found in the ash to uniquely "fingerprint" each layer and link it to one of the more than 30 eruptive centers that form the Mono Craters chain. For more information about the Mono Craters ash study see: Geochemical fingerprinting of Wilson Creek tephra layers (Mono Basin, California) using titanomagnetite compositions