A note on the extent of glaciation throughout the Himalaya during the global Last Glacial Maximum

Quantitative chronologies for the impressive glacial successions that occur throughout the Himalaya have, until recently, been almost totally lacking. Within the last decade two new techniques have promised to remedy this situation. These techniques, optically stimulated luminescence and cosmogenic nuclide surface exposure dating, enable the age of many glacial features to be determined and have allowed us to study the extent and timing of Himalayan glaciation in the late Quaternary. New data show that the local Last Glacial Maximum (LGM) occurred during the early part of the last glacial cycle, in most areas during marine isotope stage 3 (MIS-3). MIS-3 was a time of increased insolation, when the South Asian summer monsoon strengthened and penetrated further north into the Himalaya. The concomitant increased precipitation, occurring as snow at high altitudes, produced positive glacier mass balances, thereby allowing glaciers to advance. On the other hand, during the global LGM, similar to 18-24 ka, Himalayan glaciation was very restricted in extent, generally extending < 10 km from contemporary ice margins. Lower insolation at this time produced a weaker monsoon cycle, which in turn resulted in lower snowfall and snow accumulation at high altitudes. The modest advances that nevertheless did occur at this time are the result of reduced temperatures. (C) 2001 Elsevier Science Ltd. All rights reserved.