The Thule Islands, at the southern end of the South Sandwich island arc bordering the Scotia Sea, consist of three stratovolcanoes constructed along an E-W-trending line.  An ice-filled 1.5-2 km wide caldera truncates the summit of andesitic-dacitic Thule, the westernmost island, and a 4.3 x 4.8 km submarine caldera forms Douglas Strait between Thule and basaltic-to-dacitic Cook Island.  Another possible submarine caldera lies east of Cook Island and south of basaltic-andesite Bellingshausen, the easternmost island.  The age of Cook Island is uncertain, but steam was observed at the summit crater of Thule Island in 1962, and ash was seen on the surface of the ice there and on Bellingshausen Island, indicating possible 20th-century eruptions (Baker, 1968).  Bellingshausen Island has a youthful, relatively ice-free profile and an extensive well-preserved lava field on its southern flank.  A small explosion crater formed on the southern flank of Bellinghausen Island sometime between 1964 and 1986.