Quaternary glacial history of NW Garhwal, Central himalayas

Abstract

A first account of the Quaternary glacial history is presented for northwest Garhwal, Central Himalaya. On the basis of sediments and landforms, one glacial stage has been recognised. This is called the Bhagirathi Glacial Stage, when extensive valley glaciers advanced down the Bhagirathi valley to Jhala, 40.5 km from the snout of Gangotri Glacier. The ELA depression during this stage was ca. 640 m. The Bhagirathi Glacial Stage is constrained by optically stimulated luminescence dates of ca. 63 ka and 5 ka BP, and this glaciation is considered equivalent to the Last Glaciation elsewhere in the world. The maximum extent of ice occurred ca. 63 ka BP. This, however, does not correlate with the Last Glacial Maximum for the northern hemisphere ice sheets (20−18 ka BP). A series of sharp-crested moraines are present between 1 to 3 km beyond the snouts of most of the present glaciers. These moraines formed during the mid Holocene (<5 ka BP), termed here the Shivling Glacial Advance. Small moraines are inset into these and are dated at about 200 to 300 BP (the Bhujbas Glacial Advance; ca. 300 to 200 BP) and considered equivalent to the Little Ice Age in other parts of the world. ELA depressions of between 40–100 m and 20–60 m occurred during the Shivling and Bhujbas Glacial Advances, respectively. Since the Bhujbas Glacial Advance, there has been progressive retreat of glaciers, initially by downwasting and retreat, and then by simple retreat. This retreat has accelerated during the last few decades. Impressive paraglacial fans are associated with deglaciation representing very rapid resedimentation during and soon after ice retreat.