The Geology of the South Shetland Islands
Description / Table of Contents:
The renewed volcanic activity at Deception Island appears to be closely associated with the caldera ring fault. In 1967, a submarine eruption created a new island in Telefon Bay and there was a simultaeous eruption at the land centre, 2 km. to the east. In 1969, a 5 km. fissure opened up in the glacier on the western face of Mount Pond. There were numerous vents but the most damaging aspect of the eruption was the liberation of a large volume of glacial melt water. In the 1970 eruption a series of craters built a new ship of land across Telefon Bay, partley destroying the 1967 island. The new ejecta are remarkably variable in composition. They tend to become more basic further away from the site of the 1967 island. At any particular locality later products tend to be slightly more basic than earlier ones. The distinctive Na-rich, K-poor characteristic apparently persists right through the history of Deception Island. Two basalt types are recognized, one rich in alumina and the other rich in iron. However, the high Na : K ratio is especially accentuated in the more differentiated post-caldera rocks, to which the recent eruptives belong. The Deception Island suite differs in several essential aspects from the typical calc-alkali series. These differences may be explained by persistenf loss of volatiles inhibiting the formation of amphibole.
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81, VIII S. : Ill., Kt.