Quaternary Glaciation of the Himalaya and Adjacent Mountains

Abstract

The Himalaya and adjacent mountains are the most glaciated regions outside the polar realms. Abundant field studies, aided by remote sensing, and newly developing geochronological methods are aiding in reconstructing the timing and extent of Quaternary glaciation throughout the region. Abundant well-preserved glacial geologic evidence throughout the region shows that at least nine major regionally synchronous glacier advances occurred in the region over the past ~400 ka. The maximum extent of glaciation has been broadly defined and is characterized by extensive valley glaciers and expanded ice caps. The timing of maximum glacier extent is asynchronous throughout the region, with some areas experiencing maximum glaciation prior to the last glacial cycle (>100 ka), while in other regions it was during the early part of the last glacial (~30–70 ka), and in some regions, was possibly coincident with the global last glacial maximum (LGM) at ~18–24 ka. Glacier advances have been limited to a few kilometers beyond their present position in most regions since the LGM. The maximum glacier advance occurring during the Holocene at ~9–8 ka. The higher resolution of the Holocene glacial geologic record allows ~5 regional glacier advances to be resolved. All advances were somewhat restricted in extent. Glaciers have retreated in most areas during the last 100 years. However, in the Karakoram there has been little retreat and many glaciers have surged. Himalayan glaciation is forced by multiple drivers, and the timing and extent of glaciation is governed by a complex combination of different factors specific to each locality, including climate and microclimate regimes, topographic controls, and geomorphic and tectonic settings. Study of the Quaternary glacial history suggests that nature of future glacier fluctuations in response to human-induced climate change will be very complex and variable throughout the Himalaya and adjacent mountas.