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Hazards

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.