Images

Eruption episode 1 contains the oldest rocks in the Clear Lake Volcanic Field. The rock on the ridge in the background., located off Butts Canyon Road, is a lava flow that erupted around 2 million years ago.

Morro Rock is the westernmost peak in a chain of hills known locally as the “Morros” or the “Nine Sisters.”. It is a volcanic neck or plug composed of dacite which crystallized in the vent of a volcano and was later exposed by erosion. USGS photo by J. Ball

A southwesterly view of Mount Konocti, which is one of the largest volcanic features in the Clear Lake Volcanic Field. Buckingham Peninsula can also be seen stretching from the base of Mount Konocti into the foreground toward the eastern shore of the lake.  USGS photo by J.Ball

Ash-flow tuff (ignimbrite) on the fire road leading to the summit of Mount St. Helena, mapped as part of the intracaldera Sonoma volcanics. 

The Moraga Volcanics, one of several volcanic formations found in the Berkeley Hills Volcanic Field, frame a view of Mount Diablo to the east. The basaltic lava flows and their associated lapilli tuffs can be found in the Sibley Volcanic Regional Preserve. USGS photo by J. Ball

Geologists often break off the weathered surfaces of rocks in the field to get at the fresh, clean cores. This makes it easier to see the original mineralogy of the rock in question without oxidation, alteration, or other environmental impacts. USGS photo by D. Blatter

Geologists often break off the weathered surfaces of rocks in the field to get at the fresh, clean cores. This makes it easier to see the original mineralogy of the rock in question without oxidation, alteration, or other environmental impacts. USGS photo by D. Blatter.

These freshly excavated boulders along Spruce Grove Road are basalt, which is an iron and magnesium-rich rock that’s fairly uncommon in the Clear Lake Volcanic Field.

Eruption episode 3 is the most voluminous in the history of the Clear Lake Volcanic Field. Episode 3 rocks are of intermediate composition, primarily dacite, and make up many of the topographic high points in the field, including Mt. Konocti, where this photo is taken.

Andy Calvert and Tony Pivarunas drill into the face of a lava flow on Ash Creek Butte, a Pleistocene shield volcano northeast of Mount Shasta. USGS photo by Dawnika Blatter

USGS-Cascades Volcano Observatory geophysicist Rebecca Kramer works on station PR05, which is part of the Mount Rainier lahar detection network (Mount Rainier is pictured in the distance). The purpose of the site visit was to upgrade the power system and deploy infrasound equipment. 

Cinder cones (or scoria cones) are relatively small, steep-sided volcanoes that are constructed around a single vent when lava is ejected into the air, breaks into smaller pieces, and builds up around the sides of the vent. This photo is looking across the quarry which exposes the interior of a cinder cone east of Clearlake Oaks in the Clear Lake Volcanic Field.

Located at the midpoint of Clear Lake in Lake County, California, Buckingham Peninsula shows evidence of young explosive volcanism in the Clear Lake Volcanic Field. Little Borax Lake, enclosed within the Buckingham golf course, is a water-filled maar crater, as is Horseshoe Bay to its northeast. USGS photo by J. Ball.

Collecting samples on Cobb Mountain south of the Clear Lake Volcanic Field helps CalVO scientists unravel the eruptive history of the area. By examining these samples on the macro and micro scales, they can derive the geochemical evolution and eruption age of the lavas that form Cobb Mountain. USGS photo by Sally Stevens.

Rhyolite lavas in the Yellowstone Caldera younger than 631,000 years

Thurston Lake and Mount Konocti, Clear Lake Volcanic Field, California.

Mount Konocti as seen from the town of Clear Lake.

View of the Mammoth Mountain lava dome complex overlooking Horseshoe Lake.

Photograph of permanent eddy covariance station installed since 2014 in area of volcanic CO₂ emissions on Mammoth Mountain, California. USGS photo by Jennifer Lewicki, August 2019.

Located 50 miles north-northwest of Sacramento, Sutter Buttes are the only volcano in the Central Valley. They consist of a central core of andesite, dacite, and rhyolite domes and flows. These are surrounded by a large apron of fragmental volcanic debris.

A 3-4m (10-12 ft) high outcrop of basalt lava, part of a broader lava flow. These flows were erupted about 300,000 years ago following basalt dike intrusions in a rear-arc region of northern California. The eruptions of three of these flows are thought to have taken place within several hundred years of each other.