Fumarolic plumes are visible on the hydrothermally altered western wall of Santa Ana's inner summit crater, which contains an acidic lake. A steep descent down the NE crater wall at the far right allows access to the lake for geochemical sampling; recent surveys measured pH values of around 1. Sequences of bedded phreatomagmatic tephra layers more than 100 m thick are exposed in the background in the walls of the outer summit craters of Santa Ana volcano.

Photo by Paul Kimberly, 2002 (Smithsonian Institution).

Santa Ana