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Shaded relief map showing Lassen Volcanic National Park, with Lassen Peak labeled in the northern portion of the map, Growler & Morgan hot springs to the southwest, and the June 24 2024 swarm to the southeast
Lassen Volcanic Center earthquake swarm of June 24, 2024
Lassen Volcanic Center earthquake swarm of June 24, 2024
Lassen Volcanic Center earthquake swarm of June 24, 2024

This map shows the location of the June 24, 2024 earthquake swarm at the Lassen Volcanic Center relative to Lassen Peak and Growler & Morgan Hot Springs. Earthquakes are indicated by white, blue, and yellow circles, scaled to the earthquake size.

This map shows the location of the June 24, 2024 earthquake swarm at the Lassen Volcanic Center relative to Lassen Peak and Growler & Morgan Hot Springs. Earthquakes are indicated by white, blue, and yellow circles, scaled to the earthquake size.

Helicorder record showing dozens of tiny earthquake traces occurring over 12 hours, with each line comprising 15 minutes and earthquakes looking like drum cymbals turned on their sides.
LSIB helicorder trace from the Lassen Volcanic Center on June 24, 2024.
LSIB helicorder trace from the Lassen Volcanic Center on June 24, 2024.
LSIB helicorder trace from the Lassen Volcanic Center on June 24, 2024.

This digital helicorder record from station LSIB on the Northern California Seismic Network emphasizes the dozens of tiny earthquakes in Lassen's June 24 swarm. Earch line of the helicorder shows 15 minutes of time, with the entire record covering 24 hours.

This digital helicorder record from station LSIB on the Northern California Seismic Network emphasizes the dozens of tiny earthquakes in Lassen's June 24 swarm. Earch line of the helicorder shows 15 minutes of time, with the entire record covering 24 hours.

Microscopic view of different groundmass textures in rocks
Microscopic view of different groundmass textures in rocks
Microscopic view of different groundmass textures in rocks
Microscopic view of different groundmass textures in rocks

Microscopic view of different groundmass textures in rocks. On the left, this groundmass is a good choice for argon dating, as it consists of abundant interconnected crystals. On the right, the groundmass consists predominantly of glass (black because it does not transmit cross-polarized light) and is a poor choice for argon dating.

Microscopic view of different groundmass textures in rocks. On the left, this groundmass is a good choice for argon dating, as it consists of abundant interconnected crystals. On the right, the groundmass consists predominantly of glass (black because it does not transmit cross-polarized light) and is a poor choice for argon dating.

Mass spectrometer, used to measure the ration of atoms with different masses, in the USGS laboratory at Moffett Field, California
Mass spectrometer, used to measure the ration of atoms with different masses, in the USGS laboratory at Moffett Field, California
Mass spectrometer, used to measure the ration of atoms with different masses, in the USGS laboratory at Moffett Field, California
Mass spectrometer, used to measure the ration of atoms with different masses, in the USGS laboratory at Moffett Field, California

A mass spectrometer is used to measure the ratio of atoms with different masses—in this case, the different isotopes of argon gas, which can be used to determine the age of a volcanic rock. Left: a side view of a mass spectrometer at the USGS Argon Geochronology Laboratory in Moffett Field, CA. Right: a close-up view of the sample chamber in this mass spectrometer.

A mass spectrometer is used to measure the ratio of atoms with different masses—in this case, the different isotopes of argon gas, which can be used to determine the age of a volcanic rock. Left: a side view of a mass spectrometer at the USGS Argon Geochronology Laboratory in Moffett Field, CA. Right: a close-up view of the sample chamber in this mass spectrometer.

A geologist crouches next to a rhyolite outcrop and points to an egg-shaped mass of radiating pink minerals about the size of a cantaloupe. The rest of the rock is pocked with other egg to grapefruit sized pink crystal masses, interspersed with chunky fragments of black glassy lava.
Large spherulites in Hot Creek rhyolite lava in the Long Valley Caldera
Large spherulites in Hot Creek rhyolite lava in the Long Valley Caldera
Large spherulites in Hot Creek rhyolite lava in the Long Valley Caldera

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

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

A broad, flat plain covered in dull green sagebrush stretches away from the viewer in this panorama. The photo is being taken from a rocky hill, with snow-capped, sharp peaks on the far side of the plain and low raised hills on the right side of the photo. One geologist is sitting on the rocks at lower right and one geologist is standing and giving a peace sign.
Panoramic view of the Long Valley Caldera from its north side
Panoramic view of the Long Valley Caldera from its north side
Panoramic view of the Long Valley Caldera from its north side

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.

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.

Man with baseball cap, sunglasses, and blue shirt standing in front of volcanic crater at Mount St. Helens.
Kyle R. Anderson
Kyle R. Anderson
Kyle R. Anderson

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

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

Man standing next to rock with hat and high-vis vest. Snow covered mountain in background.
Phil Dawson at Mount Shasta
Phil Dawson at Mount Shasta
Phil Dawson at Mount Shasta

Phil Dawson, a Volcano Seismologist with the California Volcano Observatory, stands next to a volcanic rock on the flank of Mount Shasta, California.

Phil Dawson, a Volcano Seismologist with the California Volcano Observatory, stands next to a volcanic rock on the flank of Mount Shasta, California.

person with light blue button up shirt and short hair.
Joshua Crozier
Joshua Crozier
Joshua Crozier

Joshua Crozier is a Mendenhall Postdoctoral Fellow working at the USGS California Volcano Observatory

Joshua Crozier is a Mendenhall Postdoctoral Fellow working at the USGS California Volcano Observatory

A steaming hot spring and stream flow through the yellow-and-white altered rock of a hydrothermal area. A raised walkway is visible in the background.
Devil's Kitchen hydrothermal area in the Lassen Volcanic Center
Devil's Kitchen hydrothermal area in the Lassen Volcanic Center
Devil's Kitchen hydrothermal area in the Lassen Volcanic Center

Devils Kitchen in the Lassen Volcanic Region (within the bounds of the Lassen Volcanic National Park) is the second largest of Lassen's hydrothermal areas, after Bumpass Hell. Located in the Warner Valley in the southeast corner of the Park, Devils Kitchen contains boiling springs, mudpots, hot streams, and steam vents. USGS photo courtesy of Deb Bergfeld

Devils Kitchen in the Lassen Volcanic Region (within the bounds of the Lassen Volcanic National Park) is the second largest of Lassen's hydrothermal areas, after Bumpass Hell. Located in the Warner Valley in the southeast corner of the Park, Devils Kitchen contains boiling springs, mudpots, hot streams, and steam vents. USGS photo courtesy of Deb Bergfeld

In front of an outcrop of matte grey rock splotched with lichens, a young man in an orange safety vest gives a happy thumbs up and an older man sits writing notes in a small notebook and smiles at the camera. The rocks are perched on a moderate slope covered in brushy manzanita and scraggly pine trees.
CalVO geologists take paleomag samples from a basaltic andesite lava flow on Ash Creek Butte
CalVO geologists take paleomag samples from a basaltic andesite lava flow on Ash Creek Butte
CalVO geologists take paleomag samples from a basaltic andesite lava flow on Ash Creek Butte

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

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

Geophysicist works at station PR05, part of the Mount Rainier lahar detection network.
Station PR05 is part of the Mount Rainier lahar detection network.
Station PR05 is part of the Mount Rainier lahar detection network.
Station PR05 is part of the Mount Rainier lahar detection network.

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. 

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. 

A digital elevation map of Yellowstone Caldera
A digital elevation map of Yellowstone Caldera
A digital elevation map of Yellowstone Caldera
A digital elevation map of Yellowstone Caldera

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

Mount Konocti as seen from the town of Clear Lake.
Mount Konocti as seen from the town of Clear Lake.
Mount Konocti as seen from the town of Clear Lake.
Thurston Lake and Mount Konocti, Clear Lake Volcanic Field
Thurston Lake and Mount Konocti, Clear Lake Volcanic Field
Thurston Lake and Mount Konocti, Clear Lake Volcanic Field
Thurston Lake and Mount Konocti, Clear Lake Volcanic Field

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

A deep blue lake is nestled in pine forest at the foot of a rocky, hilly peak
Mammoth Mountain
Mammoth Mountain
Mammoth Mountain

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

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

Eddy covariance station at Mammoth Mountain, California
Eddy covariance station at Mammoth Mountain, California
Eddy covariance station at Mammoth Mountain, California
Eddy covariance station at Mammoth Mountain, California

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.

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.

Rear-arc basalt lava outcrop
Rear-arc basalt lava outcrop
Rear-arc basalt lava outcrop
Rear-arc basalt lava outcrop

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.

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.

A two part figure with a shaded-relief map view of the Long Valley Caldera marked with the outlines of its resurgent dome, Mammoth Mountain, Crowley Lake, the caldera outline, and major roads. Below is a west-to-east cross-section cartoon of the caldera, showing the locations of these features as well as the depth of caldera fill, basement rocks, and the paths of cold and hot water near magmatic intrusions.
Simplified geologic map (left) and diagrammatic cross section (right) of Long Valley Caldera.
Simplified geologic map (left) and diagrammatic cross section (right) of Long Valley Caldera.
Simplified geologic map (left) and diagrammatic cross section (right) of Long Valley Caldera.

Simplified geologic map (left) and diagrammatic cross section (right) of Long Valley Caldera. The resurgent dome, Doe Ridge, Mammoth Mountain, and the Inyo Craters and Domes all reflect volcanic activity since 760,000 years ago, when a giant eruption formed the caldera.

Brown landscape with volcano in the background
Mount Shasta, a steep-sided Cascade Range stratovolcano in Northern Ca
Mount Shasta, a steep-sided Cascade Range stratovolcano in Northern Ca
Mount Shasta, a steep-sided Cascade Range stratovolcano in Northern Ca

Mount Shasta, a steep-sided Cascade Range stratovolcano in Northern California, looms above Little Glass Mountain, a thick obsidian flow erupted from the Medicine Lake shield volcano about 1,000 years ago. These are just two of the young volcanic areas monitored by the USGS California Volcano Observatory. USGS photo.

Mount Shasta, a steep-sided Cascade Range stratovolcano in Northern California, looms above Little Glass Mountain, a thick obsidian flow erupted from the Medicine Lake shield volcano about 1,000 years ago. These are just two of the young volcanic areas monitored by the USGS California Volcano Observatory. USGS photo.

High-resolution, bare-earth, airborne light detection and ranging (...
Lidar image of Rocky Ridge and raised shorelines along Lake Tahoe
Lidar image of Rocky Ridge and raised shorelines along Lake Tahoe
Lidar image of Rocky Ridge and raised shorelines along Lake Tahoe

High-resolution, bare-earth, airborne light detection and ranging (LiDAR) image, looking obliquely northwest into Rocky Ridge.

High-resolution, bare-earth, airborne light detection and ranging (LiDAR) image, looking obliquely northwest into Rocky Ridge.