Three volcanoes composed of subice palagonite breccia form nunataks in Marie Byrd Land, Antarctica. They have been extensively modified by glacial erosion to give numerous large corries (cirques). Two of the volcanoes are radiometrically dated, which enables estimates to be made of the rate of erosion. The estimates are based on the computation of change in volume from a frustum of a cone. Rates of denudation of 360 to 460 mm per 1,000 yr are obtained, but differences in corrie size indicate that local headward erosion is ∼ 5,800 mm per 1,000 yr and lateral erosion is 800 mm per 1,000 yr. The rates apply to relatively incompetent rock. Subaerial flows of comparable age in the same region are not as intensively eroded. Erosion is probably caused by mechanical riving induced by the freezing of melt-water, which is in turn produced by local radiation conditions in the corries. Thus, glacial erosion seems to depend upon the existence of bedrock exposed above the ice sheet and the production of melt-water from the exposed rock.