Images

Building 800 at the USGS Moffett Field campus houses shared laboratory space for multiple science centers. USGS photo by Jessica Ball.

From this vantage point, the remnants of a Clear Lake volcanic field lava flow can be seen forming the prominent ridge across Highway 20. They are iron-rich and a popular location for vineyard cultivation.

Islay Hills is a chain of peaks also known as the Nine Sisters (or “Morros”).

To sample volcanic gases, inverted funnels connected to an evacuated sample bottle by tubing are sealed over a fumarole. Painter's poles are used to reach gas vents across dangerous (hot, unstable, or fragile) ground. 

This panorama of the Long Valley Caldera, looking from north to south, shows its broad central plain, post-caldera rhyolite flows and uplift on the right, and eastern Sierra Nevada in the background. USGS photo by Jessica Ball.

The presence of spherulites indicates that a lava flow cooled quickly, and their mineralogy holds clues to its precise cooling history. USGS photo by Jessica Ball

This panoramic view of the Long Valley Caldera was taken from a lava dome on the north rim of the caldera. USGS photo by Jessica Ball

Long Valley from Bald Mountain; seismic and geodetic instrumentation are shown on a hill overlooking Long Valley Caldera and the Sierra Nevada. Photo by Alicia Hotovec-Ellis, USGS.

A prominent feature carved out of the side of Mount Konocti is the Black Forest landslide, which occurred on the eastern side of Buckingham Peak and deposited massive boulders down near the shore of Clear Lake. Determining when the landslide occurred is difficult, but two broad age constraints do exist.

Schematic illustrations of the formation of inverted topography. Top graphic: Lava flows travel in topographic lows and valleys below surrounding topographic highs. Middle graphic: The hard volcanic rock protects the underlying country rock from erosion, eroding more slowly than the surrounding topography.

The rhyolite outcrop shown here is found along Bottle Rock Rd., which gets its name from the volcanic glass that’s common within this rock unit. Rhyolite is the most silica-rich rock in the Clear Lake Volcanic Field, and Thurston Creek Rhyolite, show here, is around half a million years old.

This outcrop is along Highway 175, near Hobergs, and is comprised of andesite. Andesite contains more silica than basalt, but less than dacite.

This lava flow is one of five flows of the same composition erupted over a short period of time in the High Valley area. The Round Mountain cinder cone in this area is related to these flows, and all are basaltic andesite, a rock with slightly more silica than basalt and slightly less than andesite.

Rhyodacite has more silica than dacite and less than rhyolite. This flow-banded rhyodacite is gorgeous in outcrop and is around a half million years old.

The cinder cone in the distance is Round Mountain, which is being actively quarried for road rock. Eruption episode 4 is the most recent in the Clear Lake Volcanic Field, and is characterized primarily by lava flows, cinder cones (like the one pictured), and maar deposits.

Eruption episode 2 rocks are higher in silica than those characterizing Episode 1, and instead of being primarily lava flows that filled existing valleys, Episode 2 rocks commonly erupted as volcanic domes. Cobb Mountain erupted during this episode, as did Boggs Mountain.

This view of Mt. Konocti from within the Clearlake Riviera neighborhood shows the topographic outline of the many discrete volcanic domes that comprise the mountain. Volcanic domes ooze from the ground to form steep-sided domes which can coalesce, forming mountains with multiple peaks. Mt.

The layered deposits shown in this picture were created by a maar eruption, when magma and volcanic gasses interact with groundwater to create an explosive eruption. Maar eruptions like these commonly generate craters, some of which can be seen along the western shore of Clear Lake. Soda Bay, near where this photo was taken, is a maar crater.

This lava flow of basaltic andesite composition erupted in the High Valley area. The blocky appearance of this flow top is termed 'A'ā (pronounced "ah-ah"), which is a Hawaiian term for lava flows that have a rough rubbly surface composed of broken lava blocks called clinkers. USGS photo by Dawnika Blatter

Kyle R. Anderson is a Volcano Geophysicist who works at the USGS California Volcano Observatory.

This outcropping of rocks along Morgan Valley Road is comprised of dacite, the most common composition in the Clear Lake Volcanic Field. Dacite contains more silica than basalt but less than rhyolite, so it’s commonly referred to as an “intermediate” composition.