ANTARCTIC SUBGLACIAL MELTWATER ENVIRONMENTS

A number of landform assemblages in Antarctica resulted from high magnitude subglacial floods, and their formation required water storage in subglacial lakes much larger than those beneath the present Antarctic ice sheets, The Labyrinth bears a striking resemblance to the Washington Channeled Scablands. Deep coulees, with undulating and reversed slopes, trench the floor of the Wright Valley in the McMurdo Dry Valleys. The coulees are commonly discordant at junctions: one coulee floor hangs above the bed of another. Two large, dry waterfalls at the eastern end of the Labyrinth mark floodwater plunging over the steep drop to the lower valley. The falls eroded headward leaving the Dias as a prominent landmark. Flow in blind coulees must have risen to be engulfed in inundating currents. Deep potholes sculpted interfluves, again illustrating landscape inundation by meltwater. Assuming submergence of the coulees, estimated discharges are ~ 106 m3/s. This volume of water, the undulating and reversed gradient, and water sculpted interfluves cannot be explained by steady-state hydrology, but require water storage and release. Since the Labyrinth lies close to the Trans Antarctic Mountains with no site for a subaerial lake, the reservoir lay beneath the East Antarctic Ice Sheet (EAIS). Erosional marks along the Soya Coast also indicate meltwater drainage beneath the EAIS. These marks are identical to some s-forms in Ontario, Canada, and the similarity of flow widths for the two landscapes suggests similar discharges, ~4 x 106 m3/s as calculated for the Ontario flow; again implying large reservoirs beneath the EAIS. Labyrinths with tunnel channels up to 450m deep, discordant channels, and channels with undulating long profiles and reverse slopes dominate the seascape in the Inner zones of shelf crossing troughs off the Antarctic Peninsula. Drumlins with crescentic scours in the inner zone record broad, meltwater sheet flow across the labyrinths. Thus, megafloods released from subglacial reservoirs scoured the Inner Shelf seascape. Clearly, flood water must have crossed the Middle and Outer zones. Bedforms there, attenuated drumlins and mega-scale glacial lineations, are ascribed to subglacial deformation. However, if they originated together with the labyrinths, meltwater probably sculpted them.