Explosive eruptions of Volca??n El Chicho??n in Chiapas, Mexico on March 28 and April 3-4, 1982 removed 0.2 km3 of rock to form a 1-km-wide 300-m-deep summit crater. By late April 1982 a lake had begun to form on the crater floor, and by November 1982 it attained a maximum surface area of 1.4 ?? 105 m2 and a volume of 5 ?? 106 m3. Accumulation of 4-5 m of rainfall between July and October 1982 largely formed the lake. In January 1983, temperatures of fumaroles on the crater floor and lower crater walls ranged from 98 to 115??C; by October 1983 the maximum temperature of fumarole emissions was 99??C. In January 1983 fumarole gas emissions were greater than 99 vol. % H2O with traces of CO2, SO2, and H2S. The water of the lake was a hot (T = 52-58??C), acidic (pH = 0.5), dilute solution (34,046 mg L-1 dissolved solids; Cl/S = 20.5). Sediment from the lake contains the same silicate minerals as the rocks of the 1982 pyroclastic deposits, together with less than 1% of elemental sulfur. The composition and temperature of the lake water is attributed to: (1) solution of fumarole emissions; (2) reaction of lake water with hot rocks beneath the lake level; (3) sediments washed into the lake from the crater walls; (4) hydrothermal fluids leaching sediments and formational waters in sedimentary rocks of the basement; (5) evaporation; and (6) precipitation. ?? 1984.
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Crater lake and post-eruption hydrothermal activity, El Chicho??n Volcano, Mexico