CHRONOSTRATIGRAPHY OF HIMALAYAN GLACIAL FLUCTUATIONS AT THE MILLENNIAL TIMESCALE DURING THE HOLOCENE

Glaciers are shrinking in many areas of the Himalaya and Tibet. In addition, variability of the Indian summer monsoon (ISM) and the mid-latitude westerlies has increased the magnitude of geohazards in recent times in these areas. A central concern is our limited knowledge about the close interaction between prevailing climate systems and mountain glaciers in the past, especially during the present interglacial when northern-hemisphere experienced several short-lived and high-amplitude cooling relapses. To address the problem we are reconstructing a sub-millennial timescale chronostratigraphy of Holocene glacial fluctuations in the NW Himalaya, Northern India. We are using geomorphic mapping and cosmogenic surface exposure dating of relatively younger moraines which are well preserved and abundant in the Himalayan orogen. Thirteen different glacial valleys in the NW Himalaya are being examined based on the relative influence of the two prevailing climate systems. Google Earth and ASTER digital elevation models are used first to identify and map the general geomorphology of these valleys. Ninety-nine new cosmogenic Be-10 and eight new Cl-36 dates from these valleys coupled with published cosmogenic ages of morainic boulders are used to reconstruct local glacial stages during the Holocene. These local glacial stages are then used to develop regional stages of glacial advances. Several short-lived regional glacial advances may experience at ~11.4, ~9.1, ~8.1, ~5.4, 3.8, ~2.3, 0.7, and 0.4 ka in the Himalaya-Tibetan orogen during the Holocene. New cosmogenic ages indicate widespread but restrictive glacial advances during the Little Ice Age (LIA) in the arid and semi-arid regions of the NW Himalaya. Evidence of older Holocene glacial advances are tentative in these areas due to limited available cosmogenic ages and/or large spreading of ages. The monsoon dominated regions may experience largest extension during the early Holocene and also at the start of the Neoglaciation (3.8 ka) whereas the LIA advance was limited but well preserved. Overall the Holocene glacial advances were restricted in the Himalayan-Tibetan orogen and short-lived. These short-duration changes during the late Holocene are often correlated with the decline of/changes in civilizations and dynasties in the Indian subcontinent and China.