Logo link to homepage

Clear Lake Volcanic Field

Photo of this volcano
  • Country
  • Volcanic Region
  • Landform | Volc Type
  • Last Known Eruption
  • 38.97°N
  • 122.77°W

  • 1,439 m
    4,721 ft

  • 323100
  • Latitude
  • Longitude

  • Summit
    Elevation

  • Volcano
    Number


Most Recent Bulletin Report: June 1992 (BGVN 17:06) Citation IconCite this Report

50 small seismic events triggered by M 7.5 earthquake hundreds of km away

Southern California's largest earthquake since 1952, M 7.5 on 28 June, appeared to trigger seismicity at several volcanic centers in California. It was centered roughly 200 km E of Los Angeles. In the following, David Hill describes post-earthquake activity at Long Valley caldera, and Stephen Walter discusses the USGS's seismic network, and the changes it detected at Lassen, Shasta, Medicine Lake, and the Geysers.

In recent years, the USGS northern California seismic network has relied upon Real-Time Processors (RTPs) to detect, record, and locate earthquakes. However, a film recorder (develocorder) collects data from 18 stations in volcanic areas, primarily to detect long-period earthquakes missed by RTPs. The film recorders proved useful in counting the post-M 7.5 earthquakes, most of which were too small to trigger the RTPs.

The film record was scanned for the 24 hours after the M 7.5 earthquake, noting the average coda duration for each identified event. Some events may have been missed because of seismogram saturation by the M 7.5 earthquake. Marked increases in microseismicity were observed at Lassen Peak, Medicine Lake caldera, and the Geysers (table 1). No earthquakes were observed at Shasta, but the lack of operating stations on the volcano limited the capability to observe small events.

Table 1. Number of earthquakes at northern California volcanic centers during 24-hour periods following major earthquakes on 25 April (40.37°N, 124.32°W; M 7.0) and 28 June (34.18°N, 116.47°W; M 7.5) 1992. Events with coda durations less than or equal to 10 seconds and greater than 10 seconds are tallied separately. Earthquakes were identified from film records of seismograms from nearby stations. Courtesy of Stephen Walter.

Volcanic center Lassen Lassen Shasta Shasta Medicine Lake Medicine Lake Geysers Geysers
Codas (seconds) 0-10 11+ 0-10 11+ 0-10 11+ 0-10 11+
25 Apr 1992 0 0 0 1 0 0 7 2
28 Jun 1992 8 14 1 5 12 0 46 4

Film was also scanned for the 24 hours following the M 7.0 earthquake at 40.37°N, 124.32°W (near Cape Mendocino) on 25 April. Although smaller than the 28 June earthquake, its epicenter was only 20-25% as far from the volcanoes. Furthermore, both the 25 April main shock and a M 6.5 aftershock were felt at the volcanic centers, but no felt reports were received from these areas after the 28 June earthquake. Only the Geysers showed any possible triggered events after the 25 April shock. However, background seismicity at the Geysers is higher than at the other centers, and is influenced by fluid injection and withdrawal associated with intensive geothermal development.

Geysers geothermal area report. Film records showed 50 small events in the 24 hours following the M 7.5 earthquake, 46 of which had coda durations

Information Contacts: Stephen Walter and David Hill, MS 977, U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025 USA.

The Global Volcanism Program has no Weekly Reports available for Clear Lake Volcanic Field.

Bulletin Reports - Index

Reports are organized chronologically and indexed below by Month/Year (Publication Volume:Number), and include a one-line summary. Click on the index link or scroll down to read the reports.

06/1992 (BGVN 17:06) 50 small seismic events triggered by M 7.5 earthquake hundreds of km away




Information is preliminary and subject to change. All times are local (unless otherwise noted)


June 1992 (BGVN 17:06) Citation IconCite this Report

50 small seismic events triggered by M 7.5 earthquake hundreds of km away

Southern California's largest earthquake since 1952, M 7.5 on 28 June, appeared to trigger seismicity at several volcanic centers in California. It was centered roughly 200 km E of Los Angeles. In the following, David Hill describes post-earthquake activity at Long Valley caldera, and Stephen Walter discusses the USGS's seismic network, and the changes it detected at Lassen, Shasta, Medicine Lake, and the Geysers.

In recent years, the USGS northern California seismic network has relied upon Real-Time Processors (RTPs) to detect, record, and locate earthquakes. However, a film recorder (develocorder) collects data from 18 stations in volcanic areas, primarily to detect long-period earthquakes missed by RTPs. The film recorders proved useful in counting the post-M 7.5 earthquakes, most of which were too small to trigger the RTPs.

The film record was scanned for the 24 hours after the M 7.5 earthquake, noting the average coda duration for each identified event. Some events may have been missed because of seismogram saturation by the M 7.5 earthquake. Marked increases in microseismicity were observed at Lassen Peak, Medicine Lake caldera, and the Geysers (table 1). No earthquakes were observed at Shasta, but the lack of operating stations on the volcano limited the capability to observe small events.

Table 1. Number of earthquakes at northern California volcanic centers during 24-hour periods following major earthquakes on 25 April (40.37°N, 124.32°W; M 7.0) and 28 June (34.18°N, 116.47°W; M 7.5) 1992. Events with coda durations less than or equal to 10 seconds and greater than 10 seconds are tallied separately. Earthquakes were identified from film records of seismograms from nearby stations. Courtesy of Stephen Walter.

Volcanic center Lassen Lassen Shasta Shasta Medicine Lake Medicine Lake Geysers Geysers
Codas (seconds) 0-10 11+ 0-10 11+ 0-10 11+ 0-10 11+
25 Apr 1992 0 0 0 1 0 0 7 2
28 Jun 1992 8 14 1 5 12 0 46 4

Film was also scanned for the 24 hours following the M 7.0 earthquake at 40.37°N, 124.32°W (near Cape Mendocino) on 25 April. Although smaller than the 28 June earthquake, its epicenter was only 20-25% as far from the volcanoes. Furthermore, both the 25 April main shock and a M 6.5 aftershock were felt at the volcanic centers, but no felt reports were received from these areas after the 28 June earthquake. Only the Geysers showed any possible triggered events after the 25 April shock. However, background seismicity at the Geysers is higher than at the other centers, and is influenced by fluid injection and withdrawal associated with intensive geothermal development.

Geysers geothermal area report. Film records showed 50 small events in the 24 hours following the M 7.5 earthquake, 46 of which had coda durations

Information Contacts: Stephen Walter and David Hill, MS 977, U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025 USA.

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.

Eruptive History

The Global Volcanism Program is not aware of any Holocene eruptions from Clear Lake Volcanic Field. If this volcano has had large eruptions (VEI >= 4) prior to 12,000 years ago, information might be found on the Clear Lake Volcanic Field page in the LaMEVE (Large Magnitude Explosive Volcanic Eruptions) database, a part of the Volcano Global Risk Identification and Analysis Project (VOGRIPA).

Deformation History

There is no Deformation History data available for Clear Lake Volcanic Field.

Emission History

There is no Emissions History data available for Clear Lake Volcanic Field.

Photo Gallery

Mount Konocti, a twin-peaked complex dacitic volcano of Pleistocene age on the south-central shore of Clear Lake, is the most prominent feature of the Clear Lake volcanic field. Wright Peak (left) is a rhyodacitic and dacitic lava dome with associated lava flows, and Buckingham Peak (right) is composed of dacitic lava flows capped by an eroded basaltic-andesite cinder cone. The flat ridge extending across the photo in front of Mount Konocti is a peninsula of Cretaceous-Jurrasic rocks of the Franciscan formation.

Photo by Lee Siebert, 1967 (Smithsonian Institution).
Mount Konocti, seen here beyond the southern shore of Clear Lake, is the largest feature of the Clear Lake volcanic field in the northern California Coast Ranges. The volcanic field contains lava dome complexes, scoria cones, and maars. It is located far to the west of the Cascade Range.

Photo by Lee Siebert, 1997 (Smithsonian Institution).
Elongated Rattlesnake Island near the NE tip of Clear Lake is seen here from the NW. Most of the flat-lying western side of the island is a basaltic-andesite lava flow of late-Pleistocene age. The flow was erupted to the NE and NW from a cinder cone that is the gently rounded ridge that forms the far southern tip of the island at the left. The scoriaceous aa flow was erupted subaerially above the lake level.

Photo by Lee Siebert, 1997 (Smithsonian Institution).
Mount Konocti, a composite dacitic volcano, rises above the southern shore of Clear Lake. The arcuate escarpment facing the lake on the the NW-most peak, Buckingham Peak (right), is a landslide scarp produced when part of the dome collapsed. A series of maars cuts the southern shore of Clear Lake, giving it a scalloped shoreline. Clear Lake itself, the largest natural freshwater lake entirely within California, is an elongated, irregular body of water more than 30 km long. It has a volcano-tectonic origin.

Photo by Lee Siebert, 1997 (Smithsonian Institution).
Brilliantly colored, bright-red oxidized scoria deposits from a cinder cone near the SE end of Clear Lake are quarried for road aggregate. The basaltic-andesite cinder cone is one of a N-S-trending chain of young cones at the eastern margin of the Clear Lake volcanic field. This the northernmost of two quarried cinder cones bissected by the highway leading into the town of Clearlake Oaks.

Photo by Paul Kimberly, 1997 (Smithsonian Institution).
Round Mountain (center), seen here from the WNW with the hills of the California Coast Range in the background, is one of a series of basaltic-andesite cinder cones erupted along a N-S-trending line at the eastern margin of the Clear Lake volcanic field. These cones form some of the youngest products of the volcanic field. Lava flows from Round Mountain extend west into High Valley (lower right) and east to the North Fork Cache River. The background hills are composed of Cretaceous-Jurrasic metamorphic rocks of the Franciscan formation.

Photo by Paul Kimberly, 1997 (Smithsonian Institution).
Round Mountain, seen here from the west, rises above the floor of High Valley. Round Mountain is the northernmost of a N-S-trending chain of basaltic-andesite cinder cones at the eastern end of the Clear Lake volcanic field. A lava flow from Round Mountain underlies part of the High Valley. Many of the basaltic-andesite and andesitic lava flows of the Clear Lake field are contaminated with crustal materials. They often contain xenocrysts of quartz up to several cm in size that are known locally as "Lake County Diamonds."

Photo by Paul Kimberly, 1997 (Smithsonian Institution).
The Geysers steam field is located at the SW end of the Clear Lake volcanic field in the Coast Ranges of western California. A large silicic magma reservoir provides the heat source.

Photo by Paul Kimberly, 1997 (Smithsonian Institution).
GVP Map Holdings

Maps are not currently available due to technical issues.

The maps shown below have been scanned from the GVP map archives and include the volcano on this page. Clicking on the small images will load the full 300 dpi map. Very small-scale maps (such as world maps) are not included.

Smithsonian Sample Collections Database

There are no samples for Clear Lake Volcanic Field in the Smithsonian's NMNH Department of Mineral Sciences Rock and Ore collection.

External Sites