Abstract

Eruptions of six active volcanoes in Central America provided 57 volcanic ash samples in the past 7 yrs which were unaffected by rain. The ash samples were leached with water which was analyzed for Cl, F, SO4, Na, Ca, Mg, K, Mn, Zn, and Cu, all of which were usually present. The analytical data were examined in terms of time of eruption, eruptive cycle, and physical character of the vent. It was found that the leachate material came primarily from the surface of ash particles, consisted of chemicals commonly found in volcanic gases and sublimates, and was more abundant in ash from a deep vent. It was concluded that much of the soluble material was deposited on the ash surface from volcanic gas during eruption.

Isopach mapping indicated that the total amount of ash falling within the 2.5-mm-thickness contour during the 48-day eruption of Cerro Negro in 1968 was 17 million tons; more than 21,000 tons of soluble material were contained in this ash. If projected to the world scale and over geologic time, the soluble material on volcanic ash appears to account for the Cl and SO4 which Rubey (1951) found to be in excess in the oceans.

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