Pleistocene volcanism and shifting shorelines at Lake Tahoe, California

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recently-published study co-authored by two CalVO scientists brings attention to the role that lava dams played in shaping Lake Tahoe.

New radiometric argon ages have revealed that between 2.3 and 0.94 million years ago, a small volcanic field in the northwestern Lake Tahoe basin produced basaltic lava flows that dammed the lake three separate times. These 'lava dams' raised the lake level level dozens to hundreds of feet and created raised shorelines. In addition, deltas of brecciated (fragmented) lava, pillow basalts, and tuff cones were formed where lava flows entered the lake - deltas and tuff cones when it reacted explosively with the water, and pillow basalts when the entry was less violent.

The repetitive timing of this volcanic activity poses some interesting questions about hazards. The Lake Tahoe area is not currently considered to be volcanically active (it must have had an eruption in the last 10,000 years to meet that criteria). However, if magma were to return to the area, future eruptions and new lava dams would pose a flooding hazard both around the Lake Tahoe basin and beyond. Lava dams are known to fail rapidly, and a dam that raised the level of the lake and then collapsed could cause serious flooding downstream along the Truckee River. For now, however, there is no danger of an eruption, and such an event might be hundreds of thousands or even millions of years in the future - or might never occur at all.

Kortemeirer, W., Calvert, A., Moore, J.G., Schweickert, R., 2018, Pleistocene volcanism and shifting shorelines at Lake Tahoe, California: Geosphere, vol. 14, no. 2, 23 p. doi: 10.1130/GES01551.1.