Lassen Peak Eruption 100th Anniversary - May, 2015
May 19, 2015
2015 marks the centennial of the May 22, 1915 explosive eruption of Lassen Peak. The eruption forever altered an already dynamic landscape and led to the creation of a national park which serves as a place of discovery for curious visitors and a living laboratory for a variety of scientists.
USGS California Volcano Observatory and Lassen Volcanic National Park have teamed up to celebrate the eruption anniversary with several events to be held at the park over the Memorial Day weekend. Centennial resources and a schedule of events can be found on our 1915 eruption resource page.
Mount Shasta earthquake series poses no immediate hazard
April 03, 2015
Since February 19, 2015 an ongoing series of small earthquakes has been occurring approximately 5 miles southeast of the summit of Mount Shasta, near the Clear Creek Trailhead on a regional, unnamed fault at about 3-5 miles depth. To date, twenty events at or above magnitude M1.0 have been recorded, the largest of which, a M2.1, occurred on April 1. A single M1.1 earthquake was recorded beneath the summit of the volcano on March 17. The current earthquake series poses no immediate hazard, but it is notable given the low overall background seismicity observed at Mount Shasta. The typical number of earthquakes per year tally to about ten events concentrated southeast of the summit between 5 to 10 miles away.
In addition to the ongoing earthquake series, seismic stations recorded a modest rock avalanche on the south flank of the mountain on March 30, at 18:20 PST. Smaller rock falls shook seismometers in the minutes preceding this event. The rock slide appears to be unrelated to the ongoing earthquakes series, as no earthquakes preceded the rock slide event.
CalVO and Lassen Fact Sheets Published
December 10, 2014
We are pleased to announce the publication of two new Fact Sheets relevant to CalVO.
Published overview of low-level unrest in the Long Valley Caldera, eastern California
October 31, 2014
A cataclysmic eruption of 600 km3
of rhyolite magma (Bishop Tuff) about 760,000 years ago resulted in the collapse of the partially evacuated magma chamber to form the present 17 by 32 km (10 by 20 mi) Long Valley Caldera. Although the most recent eruptions within the caldera occurred about 50,000 years ago, Long Valley Caldera remains thermally active and has had significant seismicity and deformation since at least 1978. USGS scientists have monitored geologic unrest in Long Valley Caldera since 1980, when they detected dome-like swelling in the middle of the caldera after a swarm of strong earthquakes. The new U.S. Geological Survey Open-File Report 2014–1222
by CalVO geologist Stuart Wilkinson and colleagues documents the seismicity and deformation in the Long Valley Caldera over the past decade.