lake volcano 500.jpg



So you feel really good about driving your electric car when necessary, otherwise riding your bicycle, filling the landfill with mercury from your pigtailed light bulbs, moving into a smaller living space, reusing barely soiled paper products, composting etc. in order to save the planet. But will all your effort to save the planet from mankind be all for not?


There are numerous volcanoes throughout the United States that are capable of ending most of, if not all life on the North American continent. Yellowstone supervolcano comes to mind. But even closer to home is the Clear Lake volcanic field that the USGS has compared to Yellowstone.




Clear Lake Volcanic Field is located about 90 miles north of San Francisco, California. The town of Clearlake lies within the volcanic field as does much of the 43,000-acre fresh water lake of its namesake. The Geysers steam field, which sits at the southwest margin of the volcanic region, is host to one of the world's most productive geothermal power plants, producing enough electricity for 850,000 homes. The heat driving the geothermal system emanates from a zone of partially molten rock (magma) deep below the greater Clear Lake volcanic system. The most prominent volcanic feature is 300,000 year-old Mount Konocti, rising about 3,200 ft above the southwestern shore of the lake. The most recent eruptions occurred about 11,000 years ago around Mount Konocti. Although Clear Lake volcanic field has not erupted for several millennia, sporadic volcanic-type earthquakes do occur, and the numerous hot springs and volcanic gas seeps at in the area point to its potential to erupt again. Monitoring in the Clear Lake region by the USGS and a collaborative effort with Calpine Corporation in the Geysers Steam Field, provides real-time tracking of earthquake activity. In addition, the USGS periodically analyzes volcanic gases and hot springs in the region.


Very High Threat Potential

Lassen Volcanic Center (Shasta County)

Long Valley Caldera (Mono County)

Mount Shasta (Siskiyou County)


High Threat Potential

Clear Lake Volcanic Field (Lake County)

Medicine Lake (Siskiyou & Modoc Counties)

Mono-Inyo Chain (Mono County)

Salton Buttes (Imperial County




Eruptive history of Clear Lake Volcanic Field from the USGS website


LAKE VOL.jpgThe Clear Lake Volcanics erupted during four periods of time beginning at about 2 Ma (million years ago). There is a general decrease in age northward from 2 Ma in the south to about 10,000 years in the north. Geophysical data suggests there is currently a spherical to cylindrical magma chamber about 8.7 mi in diameter and about 4.3 mi from the surface. Seismic studies indicate that the vertical extent is approximately 18.6 mi deep.


The complex eruptive history over the past 2 million years and the 10,000-year age of the youngest eruption indicate that the Clear Lake magmatic system is not extinct and that future eruptions are likely. Such a long period of multiple volcanic events and the large volume (approximately 335 cubic mi) magma chamber suggest that the Clear Lake system could be in pre caldera early evolutionary stage. Like other, similar, silicic magma systems, such as Long Valley, California; Valles, New Mexico, and Yellowstone, Wyoming, large-scale caldera forming eruptions could erupt huge volumes of ash and tephra leading to volcanic hazards such as pyroclastic flows.


lake knocti 300.jpgMount Konocti is a 4,305 ft mountain that dominates the view of the eastern shore of Clear Lake. It began forming its major edifice approximately 350,000 years ago, though core samples have been dated to 480,000 years ago. Dacites from these early forming eruptions vented in a west- northwest-trending zone, which culminated at the northwest end of the Mount Konocti edifice. This mountain contains the largest volume of dacite in the Clear Lake Volcanic Field and must have been fed from a sizeable magma chamber.


It is difficult to strictly compare the eruptive history of the Clear Lake Volcanics area to any other historically or presently active volcanic system within California. Clear Lake field is unlike both the Sonoma Volcanics to the south and the Cascades volcanoes to the north. The 2 million year volcanic history of the Clear Lake field is highly episodic, with long lulls in activity separated by shorter intervals of frequent eruptions. At present, the system appears to be in a lull following a volcanically busy stretch between 60,000 and 10,000 years ago, which averaged 1 eruption every 1,800 years. Because of long pauses in the volcanic activity near Clear Lake, it is currently uncertain what stage of volcanism the region might be undergoing. Intermittent seismic activity and the presence of heat at depth indicate that the system is still active and eruptions are likely.


If the magma chamber beneath the Clear Lake field were tapped again, eruptions might occur in the lake. These eruptions would be phreatomagmatic and would pose ash-fall and wave hazards to the lakeshore and ash-fall hazards to areas within a few kilometers of the vent. Eruptions away from the lake would produce silicic domes, cinder cones and flows and would be hazardous within a few kilometers of the vents. Future eruptions would be signaled by heightened earthquake activity.


Mining and mineralization of the Clear Lake region

The Geysers-Clear Lake area has been one of the most productive in the United States for mercury, and gold was mined in the late 1800s. Many of the deposits are directly associated with outcrops of early Clear Lake volcanic rocks. For over a century, a correlation has been known between the mercury ore deposits, thermal springs, and volcanism at Clear Lake.


The Geysers Geothermal Field

Despite the name of the steam field, no natural geysers exist anywhere in the Geysers-Clear Lake area. The name was suggested to early explorers by the fumarolic activity and steam rising from hot springs in what later became the earliest developed part of the steam field. The steam field is adjacent to the southwest edge of the Quaternary Clear Lake volcanic field. The geothermal field includes the 1.66 Ma basalt of Caldwell Pines and wraps around the northwest and south sides of the 1.0 to 1.1 Ma rhyolite and dacite domes of Cobb Mountain.


lake soils 460.jpg











“ nation under God,..”
Free counters provided by Andale