deltas, and meltwater drained away, leading to the formation of diverse structures within the hyaloclastite deltas. The deltas may have formed during ice highstands 66,000 and 22,000–15,000years ago. Geology The West Antarctic Rift System is a basin and range province similar to the Great Basin in North America; it cuts across Antarctica from the Ross Sea to the Bellingshausen Sea. The Rift became active during the Mesozoic. Owing to thick ice cover it is not clear whether it is currently active, and there is no seismic activity. Most of the Rift lies below sea level. To the south it is flanked by the Transantarctic Mountains and to the north by the volcanic province of Marie Byrd Land. Volcanic activity in Marie Byrd Land commenced about 34million years ago, but high activity began 14million years ago. A major uplifted dome, in width, is centred on the Amundsen Sea coast and is associated with the Rift. About 18 central volcanoes were active in Marie Byrd Land from the Miocene to the Holocene. Among the volcanic areas in Marie Byrd Land are the Flood Range with Mount Berlin, the Ames Range, the Executive Committee Range with Mount Sidley and Mount Waesche, the Crary Mountains, Toney Mountain, Mount Takahe and Mount Murphy. These volcanoes mainly occur in groups or chains, but there also are isolated edifices. Mount Takahe is located in the eastern Marie Byrd Land volcanic province and with an estimated volume of could be the largest of the Marie Byrd Land volcanoes, comparable to Mount Kilimanjaro in Africa. Most of these volcanoes are large, capped off by a summit caldera and appear to have begun as fast-growing shield volcanoes. Later, calderas formed. Eventually, late in the history of the volcanoes parasitic vents were active. The volcanoes are all surmounted by rocks composed of trachyte, phonolite, pantellerite, or comendite. Their activity has been attributed either to the reactivation of crustal structures or to the presence of a mantle plume. The volcanoes rise from a Paleozoic basement. Mount Takahe may feature a large magma chamber and a heat flow anomaly underneath the ice has been found at the volcano. A magnetic anomaly has also been linked to the mountain. Composition Trachyte is the most common rock on Mount Takahe, phonolite being less common. Basanite, hawaiite, and mugearite are uncommon, but the occurrence of benmoreite and pantellerite has been reported, and some rocks have been