Geologist Bill Evans noting observations at the thermal springs (pouring from the outcrop center of photograph), located at the base of the central intracaldera cone in Ugashik caldera. The warmest of these several springs was 21.7°C with a pH of 5.71. Chemical anaylsis of these waters can be found in Table 1 of Evans and other, 2009, "Diffuse gas emissions at the Ukinrek Maars, Alaska: Implications for magmatic degassing and volcanic monitroing", Applied Geochemistry, v. 24, p. 527-535.
Image courtesy of AVO/USGS.
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