Ice-Cored Moraines and Ice Diapirs, Lake Miers, Victoria Land, Antarctica

Abstract

Abstract Lake Miers is covered by a thick ice sheet which is domed over most of its area and thrust into sharp debris-covered ridges around its margin. Ridges result largely from compression generated in the ice raft by freeze and thaw. Apart from a narrow moat in summer the ice round the lake shore is frozen fast to the lake bed. The margin of the floating ice raft is thrust over the fast shore ice to form pressure ridges. In the prevailing aridity the ridges ablate relatively swiftly and an equilibrium is attained between the rates of uplift and downwasting. With continued uplift the infrozen gravels migrate to the surface of the ridges and accumulate there as a residual cover. Because of its low albedo the debris cover causes locally increased insolation, and because it is thin, heat is conducted to the underlying ice and ablation is increased. These active and young moraines are quite different from passive and ancient ice-cored moraines. The latter are preserved only because of a thick and insulating debris cover: the Lake Miers ridges exist despite their thin insolating gravel cover and primarily because they are dynamic. Ice domes in the centre of the lake are related to the ridges and are in part caused by the same compressive forces but they are in part due to the upwelling of the ice in diapirs. Thin patches of gravel on the surface of the ice cause locally increased insolation and ablation. The ice is thus melted down to the level of the water in the lake. This local unloading favours the arching of the ice by upward water pressure and the concomitant thinning and weakening favour further compressional doming on the same site. The arching process is dynamic and self-perpetuating and when continued for several years becames diapiric.