Antarctica

The Antarctic Peninsula has been the focus of continental margin calc-alkaline magmatism for at least 200 million years (e.g. Pankhurst, 1982; Saunders et al., 1982; Weaver et al., 1982; Thomson and Pankhurst, 1983) and has experienced repeated mafic alkaline eruptions for the last 7 million years (e.g. Smellie, 1987; Smellie et al., 1988; Hole, 1988). During this time, the Antarctic ice sheet has waxed and waned, resulting in numerous late Cenozoic glaciovolcanic sequences throughout the Antarctic Peninsula. These range from small, monogenetic vents to polygenetic edifices up to 40 km across (Nelson, 1975; Smellie et al. 1988; Smellie, 1990; Rowley et al., 1990). Additionally, glaciovolcanic deposits have been recognized further west in Marie Byrd Land (LeMasurier, 1972, 1981; Palais et al., 1988), the McMurdo Volcanic Group (Wright, 1980), and the Hallett Volcanic Province (Hamilton, 1972; McIntosh and Gamble, 1987). Studies of these landforms provide important information about the Antarctic climate throughout the Cenozoic, and on glaciovolcanic and hydroclastic processes.

Some of the recent research on Antarctic glaciovolcanism has focused on the relationship between ice thickness, topography, and deposit characteristics, and it appears that ice thickness exerts a major control on the nature of the deposits formed (e.g. Smellie et al., 1993; Smellie and Skilling, 1994). Under thick ice (e.g. 400 m, as is inferred for Brown Bluff), the sequence is very similar to those seen at many Icelandic volcanoes (pillow lavas overlain by hyaloclastite units), with evidence for subglacial eruptions into ponded water, a result of the impermeability of the lower portions of a thick ice sheet. However, under thin ice (less than 150 m, as is inferred for Mount Pinafore), there is no evidence for ponded water, and meltwater appears to have drained continuously, a result of the high permeability of thin ice and firn (Smellie and Skilling, 1994). These conclusions are of great interest with regard to other glaciovolcanic settings (e.g. British Columbia, Iceland), because it may be possible to infer the thicknesses and drainage characteristics of previously existing ice sheets based on the characteristics of subglacial volcanoes.