ALBERT

Description: The glaciated Tien Shan mountain chains of Kyrgyz Republic represent the main reservoir of water supply of large parts of Central Asia. The retreat of glaciation in this area, observed since the last two decades, caused changes in the dynamics of the glaciers. Hence, especially at the largest glacier lake of Central Asia - Lake Merzbacher - the number of glacial lake outburst floods (GLOFs) raised dramatically and caused massive damage of the infrastructure of the regions situated below the glacier outflow every year. From July 22 to August 13, 2005 GeoForschungsZentrum Potsdam (GFZ), the Central Asian Institute of Applied Geosciences (CAIAG) in Bishkek and invited geoscientists from Europe jointly conducted the Inylshek 2005 expedition to Lake Merzbacher. The lake is situated at the lower end of the northern tributary valley by accumulation of melt water, blocked by the ice of Southern Inylchek glacier. A new ground-based remote observation technique utilizing GPS signals reflected from the lake's surface was installed beside the shoreline of Lake Merzbacher at 42.196°N, 79.847°E and a height of 3271 m above sea level in order to monitor changes of the lake level. Observations of the lake level showed that after the first drainage event the lake slowly refilled with measured rates of about 2-4 cm/h in water level change between July 28 and July 31. During July 31 a second dam failure happened, resulting in a drop of the water level of almost 14 m within the first 4 days. Detailed geodetic GPS measurements on the ice dam and of the glacier flow, combined with interpretation of optical and radar satellite data from several subsequent years now provide insight into the post-drainage dam response and the changed ice dynamic conditions. It could be demonstrated that during high water levels in the lake a large part of the ice dam becomes afloat, lifting the ice surface up to almost 20 m in the central dam region. During this phase of extensive floatation strong calving is facilitated, which is supported by the high density of ice debris in the lake. GFZ has teamed up with CAIAG and an international scientific team to plan the installation of a permanent service platform in the Inylchek glacier area. This platform is intended to provide the necessary infrastructure to run a wide range of instruments and communication systems to provide near real-time observations of short- and long term dynamics of the Inylshek Glacier system serving as model glacier region in an undisturbed high-mountain area. In a first step a local GPS network to monitor the ice dynamics of the glacier and a local network of meteorology and hydrology stations is planned. Additionally, an enhanced GPS reflectometry instrumentation is projected for monitoring the water level of Lake Merzbacher.

Description: The retreat of glaciation in the Tien Shan mountain chains of Kyrgyz Republic can be observed since the last two decades which causes changes in the dynamics of the glaciers. Hence, especially at the largest glacier lake of Central Asia - Lake Merzbacher - the number of glacial lake outburst floods (GLOFs) raised dramatically. These GLOF events regularly occur between July and August every year and cause massive damage of the infrastructure of the regions situated below the glacier outflow. From July 22 to August 13, 2005 GeoForschungsZentrum Potsdam (GFZ), the Central Asian Institute of Applied Geosciences (CAIAG) in Bishkek and invited geoscientists from Europe jointly conducted the Inylshek 2005 expedition to Lake Merzbacher. The lake is situated at the lower end of the northern tributary valley by accumulation of melt water, blocked by the ice of Southern Inylchek glacier. A novel ground-based remote observation technique utilizing GPS signals reflected from the lake's surface was installed beside the shoreline of Lake Merzbacher at 42.196°N, 79.847°E and a height of 3271m above sea level in order to monitor changes of the lake level. A single unmodified RHCP GPS patch antenna was mounted at a secure iceberg-free location in a height of 43m above the glacier lake and was tilted 45° toward the lake surface. The 12-channel L1 frequency OpenGPS receiver allows tracking of up to 8 direct GPS signals for navigation and open-loop tracking of up to 4 independent reflected GPS signals simultaneously for altimetry. Although the lake surface was fully covered with ice floes and icebergs, the OpenGPS receiver collected several height profiles every day and monitored the temporal change of the lakes water level during 15 days, between July 27 and August 10, 2005. The replenishment of the lake could be fixed from the GPS reflectometry measurements to a rise rate of about 2cm/h, until the dam broke and the estimated water level decreased by an estimated value of about 29cm/h. Single measurements state a water level drop of 13.75m between July 31 and August 3. After the GLOF event took part, the standard deviation (STD) of the derived height profiles - used as an estimate of the surface roughness - significantly increased and the power of the reflected signal decreased by a factor of 10. The studies will be continued with a new reflectometry receiver prototype within the framework of the new German Helmholtz Research Programme 2009-2013 "Geosystem: The Changing Earth" and are part of 3 topics of the programme: (1) Planet Earth Monitoring: Global Processes and Change – innovative technologies, (2) Earth System Dynamics: Coupled Processes and Regional Impact - Central Asian Global Change Observatory, (3) Natural Hazards: Assessment and Risk Mitigation- GPS (GNSS) technologies for monitoring ice dam failures, and lake and river water level dynamics.