The maximum Ice Age (LGM) glaciation of the Central- and South Karakorum: an investigation of the heights of its glacier levels and ice thicknesses as well as lowest prehistoric ice margin positions in the Hindukush, Himalaya and in East-Tibet on the Minya Konka-massif

Abstract

A continuing prehistoric ice stream network between the Karakorum main crest and the Nanga Parbat massive has been evidenced, which, flowing down from the current Baltoro- and Chogolungma glaciers and filling the Shigar valley as well as the Skardu Basin, has flowed together with the Gilgit valley glacier to a joint Indus parent glacier through the Indus gorge. The ice stream network received an influx by a plateau glacier covering the Deosai plateau, which was connected through outlet glaciers to the ice filling of the Skardu Basin and the Astor glacier at the Nanga Parbat, as well as to the lower Indus glacier. The field observations introduced here in part confirm the results as to the Ice Age glacier surface area of Lydekker, Oestreich and Dainelli, but go beyond it. In additon, a reconstruction of the surface level of this ice stream network and its glacier thicknesses up to the highest regions of the present-day Karakorum valley glaciers has been carried out for the first time. In the area under investigation the Karakorum ice stream network showed three ice cupolas, culminating at an altitude of 6200–6400 m. Between the mountain groups towering 1000–2000 m higher up, they communicated with each other over the transfluence passes in a continuous glacier surface without breaks in slope. In the Braldu- and Basna valley ice thicknesses of 2400–2900 m have been reached. In the Skardu Basin, where the glacier thickness had decreased to c. 1500–1000 m, the ELA at an ice level of 3500-3200 m asl had fallen short to the extent that from here on down the Indus glacier a surface moraine cover has to be suggested. However, 80% of the surface of the ice stream network was devoid of debris and had an albedo of 75-90%. The lowest joint glacier terminus of the ice stream network was situated - as has already been published in 1988 – in the lower Indus valley at 850–800 m asl. The reconstructed maximum extension of the ice stream network has been classified as belonging to the LGM in the wider sense (60–18 Ka BP). Four Late Glacial glacier positions (I–IV), with a decreasing ice filling of the valleys, have been differentiated, which can be locally recognized through polish lines and lateral moraine ledges.