| Summary: | The largely snow and ice free McMurdo Dry Valleys of Antarctica are one of the coldest and driest locations on Earth. It has been proposed that during the Last Glacial Maximum (LGM) to the early Holocene large lakes up to 200m deep and 100km in area occupied these valleys. We present the first topographic survey of features reported to be shorelines from one such lake, Glacial Lake Victoria, in Victoria Valley. In combination with the analysis of laser altimetry data obtained from the NASA Airborne Topographic Mapper system and cosmogenic dating of granite boulders we show that the features previously thought to be shorelines are not horizontally or linearly continuous. Rather, we conclude that they are scars from ancient slope mass movement deposits. Be cosmogenic dating indicates that their formation is on timescales of at least 160ka before present and not 20ka as the LGM mega-lake hypothesis suggests. We conclude that the geomorphic features believed to be shorelines and which underpin the LGM mega-lake hypothesis in Victoria Valley are mass movement deposits and not lake shorelines. Our results support an emerging body of literature unable to find evidence to verify the McMurdo Dry Valleys LGM mega-lake hypothesis. Accordingly we suggest caution in invoking such significant landscape features in discussions of the environmental past of this unique region until such time as further research provides an unequivocal history of the region's geomorphic past.
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