Investigating the Impact of a Glacial Lake Flooding (GLOF) on the Inylchek Glacier Flow Regime by Means of Radar Data
Neelmeijer, Julia; Motagh, Mahdi; Wetzel, Hans-Ulrich
Helmholtz Centre Potsdam, GFZ, GERMANY

Drainage of glaciers located in Central Asia is influenced by a recent temperature increase leading not only to increased ablation rates but also to an increased risk of glacial lake development. Occurring unnoticed in remote areas, these lakes pose a sincere threat to inhabitants living further downstream close to the freshwater supply. Monitoring of such hazardous areas is a difficult task due to the limited accessibility. As a consequence, triggers of a glacial lake outburst flood (GLOF) are not well understood yet. Our target site, the Inylchek glacier, shows the special constellation of having a nested proglacial lake dammed between its two branches. This Lake Merzbacher drains on a regularly basis each year in summer time, making the Inylchek glacier to an ideal study area for investigating the impact of such a GLOF on the glacier flow regime itself.

Since Inylchek is one of the largest debris covered glaciers in the world, monitoring of the entire area is best achieved by using remote sensing data. To overcome the problem of cloud covering appearing in optical images, we relied on radar data acquired by the German TerraSAR-X sensor. By applying the feature tracking technique to the high spatial resolution X-band data, we are able to get a detailed image of the glacier's flow regime. The high temporal covering, due to the 11-days repeat time, makes it additionally possible to get not only information of the annual mean velocity, but especially monitor the seasonal surface kinematics changes.

Our results combined from ascending and descending imagery acquired in 2009/2010 show an increase of the surface flow over the ablation area from 25 cm/day in spring to a maximum peak of 45 cm/day in summer time. Particularly remarkable is the direct correlation of the distinct summer velocity peak to the annually occurring GLOF event, showing a significant influence of the drainage on the flow regime of the glacier. The investigation of the seasonal variations will be complemented by a long term velocity study over the last 10 years accomplished with the help of ENVISAT and ERS-1/2 radar data.