Images

Lassen Peak viewed from the south at the summit of Brokeoff Volcano, Lassen Volcanic National Park.

Mudpots bubble and steam near the Salton Buttes lava domes, a volcanic area at the southeastern end of the Salton Sea, California.

Chaos Jumbles (foreground) is a rockfall avalanche that formed around 340 years ago when one of the Chaos Crags domes (background) collapsed.

Chaos Crags is a series of lava domes that erupted about 1,100 years ago from the Lassen Volcanic Center.

The Neenach Volcanic Field was formed by the same eruptions as the Pinnacles, and the two were split by the movement of the San Andreas Fault over 23 million years. The remnants of the eastern part of the largely rhyolitic volcanic formations remain in Southern California,195 miles (314 kilometers) away. Photo courtesy of Garry Hayes, Modesto Junior College.

The photo includes five rhyolitic units of different ages: Unforested 2-ka rhyolite of "Devils chain" rests on forested 35,000 year old flow lobe from adjacent Devils Hill dome. Three pale-gray spurs form sharp salients that extend to elevations only 550 m (1640 ft) below the darker andesitic summit of South Sister.

Wes Hildreth and Judy Fierstein, seen here in 2009 on the east shore of Sparks Lake near Oregon's South Sister volcano, were longtime field and research partners Their work showed how mapping and understanding geologic field relationships provide an unequaled framework for interpretation of laboratory-generated data; and how well-honed curiosity, acute observat

Hot Creek Gorge viewed upstream toward the southwest; the steep walls of the gorge consist of a single rhyolite lava flow erupted from a vent 4 km (2.5 mi) to the south.

Bubbling Spring, a feature of Hot Creek in the Long Valley Caldera, California, occasionally "boils" due to high water temperature.

Soil-temperature measurement at Hot Creek in Long Valley Caldera, California.

Cinder Cone erupted in the year 1666 in the Lassen Volcanic Region of northern California.

Medicine Lake lies within the shallow basin of Medicine Lake caldera. Glass Mountain flow, draped over the east side of the volcano, is the youngest lava flow at the volcano. The northeasternmost dacite tongue extends nearly to the bottom of the photo (distal lobes are outlined to enhance visibility).

Glass Mountain obsidian flow at Medicine Lake volcano, California. Glass Mountain is a spectacular, nearly treeless, steep-sided rhyolite and dacite obsidian flow that erupted just outside the eastern caldera rim and flowed down the steep eastern flank of Medicine Lake volcano.

Hydrothermal system and water flow in the subsurface beneath Long Valley Caldera, California. Cartoon Illustration from USGS FS 2007-3045.

Aerial photo of Mount Shasta's southwestern flank in a low-snow period. The Hotlum cone is on the right, while the Shastina dome is to the left.

Hot springs and their associated rising steam may be found in Hot Spring Cove on the southeastern point of Paoha Island in the Mono Lake Volcanic Field. USGS photo by Deborah Bergfeld.

Photograph looking south across the rugged andesitic northern end of the compositionally zoned Callahan Flow toward the main vent at Cinder Butte (partly covered by snow.) USGS photograph by Tanya Blacic

Eruptions of the Yellowstone volcanic system have included the two largest volcanic eruptions in North America in the past few million years; the third largest was at Long Valley in California and produced the Bishop ash bed. The biggest of the Yellowstone eruptions occurred 2.1 million years ago, depositing the Huckleberry Ridge ash bed.

USGS scientists measuring temperature in a deep borehole in Long Valley Caldera with the Sierra Nevada mountains in the background.

USGS scientist Wes Hildreth at a 2004 Meritorious Service Award Ceremony. Photo courtesy of Mike Diggles.

Gas bubbles through a sample bottle containing alkaline solution, allowing for separation of different gas phases.