Results from the 2009 expedition to the Inylchek Glacier, Central Tien Shan (Kyrgyzstan)

The 2009 expedition led to the Inylchek Glacier in eastern Kyrgyzstan, the largest glacier of the Tien Shan with a length of 60,5 kilometers. In this paper we present the results of our investigations in the surroundings of the Northern Inylchek Glacier, namely in the Peremitschka, the seasonally flooded plain situated between the Southern Inylchek Glacier and Upper Lake Merzbacher. During the summer, this plain is flooded by melt water discharged from the Northern Inylchek Valley, creating the up to 120 m deep Lower Lake Merzbacher, which regularly bursts out and releases its water through an englacial piping system of the Southern Inylchek Glacier in. It is due to this unique phenomenon that Lower Lake Merzbacher has been the subject of study by scientists on numerous expeditions during the last century. As a mapping basis for our field works, we used an enlarged scene acquired in September 2005 from the Quickbird satellite with 60 cm ground resolution. For identification of advancing and retreating parts of the Inylchek Glacier system, a pan-sharpened Landsat 7 ETM+ scene (bands 1, 4 and 7) with a ground resolution of 15 m acquired in 2006 was used. A time series analysis of aerial photos dating from 1943 and 1956 was compared to the Quickbird scene from 2005 and revealed first the retreat and later the rapid advance of the Northern Inylchek Glacier along a distance of at least two kilometres. Since neither indications of a glacier lake outburst around Upper Lake Merzbacher nor stretched ogives or erosional scars in the Northern Inylchek Glacier implying a rapid surge could be detected, the mechanism of this fluctuating glacier is subject to ongoing investigations. Our helicopter-supported campaign in the Peremitschka at altitudes between 3300 and 3500 meters lasted only four days. For the glaciogeologic and geomorphologic interpretation of remote sensing imageries we used geophysical methods such as electric resistivity tomography (ERT) and frequency domain electromagnetics (FDEM). The 800 m long ERT-profile crossing the Peremitschka plain revealed resistivities ranging from 6 Ohmmeter (ohm.m) in the near subsurface to 100.000 ohm.m down to a depth of 45 meters. A series of thin, undulated, low-resistivity layers are underlain by a thick high-resistivity layer, which has been interpreted as dead ice from the formerly advancing Northern Inylchek Glacier. A small river flows down the Northern Inylchek Valley, here termed “Merz Rivulet” or “Merzbach”, with a flow of about 30 m3/second. Along its course it has locally eroded the Peremitschka plain to a depth of 20-25 meters. This steep slope within the Peremitschka reveals an intercalation of silty calcareous lake deposits with ice layers and ice lenses respectively. These outcrops have been interpreted as near subsurface permafrost layers, which can be correlated with the undulated low-resistivity layer of the ERT-profile. Additionally, high resolution mapping of this permafrost zone using frequency domain electromagnetics with 2525 Hertz (Hz) and 5025 Hz revealed cone-like depressions, which were interpreted as glacier karst