SUB-ICE TOPOGRAPHY AND METEORITE FINDS NEAR THE ALLAN HILLS AND THE NEAR WESTERN ICE FIELD, VICTORIA LAND, ANTARCTICA

We have investigated the glaciological causes of large meteorite concentrations on blue ice fields west and southwest of the Allan Hills in Antarctica. A sub-ice topography map for the area was prepared from data of a radio echo sounding survey. The map reveals a mesa-type paleosurface. It was formed prior to and modified by glacial processes during the initial stage of glaciation of Antarctica. Ice flow toward Mawson Glacier north of the Allan Hills is largely confined to a N-S trending depression between the Allan Hills Ice Field and the Near Western Ice Field. Blue ice at the margins of the ice stream flows over the mesas on both sides of this depression. Meteorites entrained in blue ice are uncovered by sublimation and ablation. We present arguments showing that currently almost all of the blue ice flowing into the Allan Hills Ice Field is sublimated, leaving meteorites on the ice surface. We present evidence that windblown meteorites are trapped by snow bridges across crevasses, resulting in a near-surface meteorite concentration near the ice ridges of the Allan Hills Ice Field. Nevertheless, most meteorites are exposed for only a short period of time to the atmosphere before they are blown by the wind across the ice toward the western foot of the Allan Hills, from where they are slowly carried northward to Mawson Glacier and the Ross Sea.