GLACIATIONS | Late Quaternary in Highland Asia

Abstract

Highland Asia is the most glaciated tract outside of the Polar Regions. Its vastness, inaccessibility, and political constraints have hindered the advancement of the understanding of the nature of Quaternary glaciation. In recent years, particularly with the application of newly developing dating techniques such as terrestrial cosmogenic surface exposure and optically stimulated luminescence dating, new knowledge of the timing and extent of glaciation is providing fresh insights into the complexity of climate change and glaciation in the region. Thus far, the paucity of numerical dates on moraines for most regions of High Asia makes it extremely difficult to correlate glacial advances between regions and to attribute different climatic factors to glaciation. Where programs of intensive numerical dating has been undertaken, the results suggest that glaciation (on millennial timescales) is broadly synchronous throughout Highland Asia. However, the former extent of glaciation and equilibrium-line altitude depressions varies considerably within and between different regions of High Asia. Further, the developing research suggests that the regional patterns and timing of glaciation reflect temporal and spatial variability in the south Asian monsoon and mid-latitude westerlies, and in particular regional precipitation gradients. In regions of greater aridity, the extent of glaciation has become increasingly restricted throughout the late Quaternary, leading to the preservation of old (pre-Lastglacial cycle) glacial landforms. In contrast, in regions that are strongly influenced by the monsoon, the preservation potential of pre-Lateglacial moraine successions is poor. This is possibly because Lateglacial and Holocene glacial advances may have been most extensive and hence may have destroyed any evidence of earlier glaciations. Of particular note is the progressive retreat of glaciers during the twentieth century and the concern that this will continue into the twenty-first century as a consequence of human-induced global warming.