Box 63 Glacial Meltwater Channels In The Labyrinth Evidence For Huge Subglacial Floods From The Antarctic Ice Sheet

Perhaps the most famous meltwater channel system in the world is the Labyrinth, a >50 km long network of bedrock channels and scoured terrain in front of Wright Upper Glacier in Antarctica. Lewis et al. (2006) described in detail the geomorphology of the channels that make up the Labyrinth. It consists of a number of different levels. On the upper and intermediate levels are signs of glacial erosion in the form of striations and ice-moulding. On the lower level the channels and canyons are up to 600 m wide and 250 m deep, have longitudinal profiles with reverse gradients, and contain huge potholes (>35 m deep) at tributary junctions. Lewis et al. (2006) considered these characteristics to be consistent with incision from fast-flowing subglacial meltwater, possibly related to a former subglacial outburst flood associated with episodic drainage of subglacial lakes in East Antarctica. They estimated flood discharges on the order of 1.6 to 2.2 x 106m3s-1. Using 40Ar/39Ar analyses of volcanic tephra in the Labyrinth they then showed that the channels are relict and that the last major subglacial flood occurred sometime between 14.4 and 12.4 million years ago. They also speculated that the huge discharge of large volumes of subglacial meltwater to the Southern Ocean may have coincided with, and contributed to, oscillations in regional and/or global climate at this time.

Source: Lewis, A.R., Marchant, D.R., Kowalewski, D.E., et al. (2006) The age and origin of the Labyrinth, Western Dry Valleys, Antarctica: evidence for extensive Middle Miocene subglacial floods and freshwater discharge to the Southern Ocean. Geology, 34, 513-16. [Photograph courtesy of: The Antarctic Photo Library, U.S. Antarctic Program].

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