Geothermal Hot Spots in Southern California Volcanoes

November 20, 2015



Photographers: David K. Lynch; Paul M. Adams
Summary Authors: David K. Lynch; Paul M. Adams
November 2015 Viewer's Choice
Southern California’s Salton Trough forms as the North American and Pacific tectonic plates move away from each other and leave a depression in the crust. Such motion creates an opening to the mantle allowing magma to ooze upward. Though still many kilometers below the overlying Colorado River sediments, this relatively shallow magma body raises the geothermal gradient. Occasionally, some of the magma reaches the surface. When this happens, volcanoes form. Thousands of years ago the Salton Buttes, five rhyolitic volcanic domes that project upwards a hundred or so feet above the surrounding plain, were created this way. Unlike the stratovolcanoes of the Cascade Range far to the north produced by subduction, the Salton Butte magma probably seeped upwards rather gently and without massive eruptions. Today they're quiescent, but one of them has a number of hot spots that bear witness to their origin.
On the south flank of Red Island's north dome, at least six vents are present that are hot enough to stand out in thermal imagery. While none is more than about 100 F (38 C), this is hot enough to suggest that a heat source is still present. Perhaps it’s a remnant of ancient volcanism or a magma body close to the surface. The first picture shows pairs of images of two of the hot vents, visible and thermal. The second shows a cloud of condensed water vapor emerging from one of the vents.

These hot spots were discovered in 2013 during a nighttime search based on anecdotal reports that a single hot vent “was up there somewhere.” Two were discovered using the infrared camera, and three by seeing condensed moisture on the cooler surface rock. The sixth was found the old-fashioned way: by sticking our hands into crevasses between the jumbled rock and feeling warmth.