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Future volcanic activity at Clear Lake

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 1,400 km3, 335 mi3) 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. However, if the heat source at depth moves within the Clear Lake region, it is possible that there will not be enough magma generation or gas build up necessary for a large-scale ash-flow eruption.

Although future eruptions are likely in the Clear Lake field, prediction of the timing is difficult because activity has been episodic in the past. From dates and numbers of ash beds beneath Clear Lake, and the apparent lack of eruptions in the past 10,000 years is a geologically brief lull in activity after frequent eruptions (about 34, or averaging one every 1,800 years) in the previous 60,000 years. Episodes of volcanic activity have typically continued for at least 0.3 million years, so that the youngest episode, which began about 0.1 Ma, could be in an early stage and may continue for another 0.2 Ma.

Eruptions are likely to be located close to, beneath, or northeast of Clear Lake, especially around the east arm of the lake. Phreatomagmatic eruptions would occur near the lake 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 cinder cones and flows and would be hazardous within a few kilometers of the vents.