Changes in Merzbacher Lake of Inylchek Glacier and Glacial Flash Floods in Aksu River Basin,Tianshan during the Period of 1903-2009

The Kumarik River,which is the headwater of theAksu Riverand from the glaciated centre of Central Asia in the Mount Khan Tengry of Tianshan,drainage area of 12 816 km2(which of 2 306 km2in Kyrgyzstan) in which glacier area is 3 195 km2. Inylchek Glacier is the largest one with 61km length and an area cover of 748.4 km2. The glacial runoff is 54% of average annual runoff at Shehel Gauge Station. In the source region of Kumarik River,sandwiched between the South and the North Inylchek Glaciers,is the mysterious Merzbacher Lake,whichis thelargest glacial lakein Sary Jaz -Kumarik River Basin. Every year,and sometimes twice a year,the lake suddenly empties,only to refill again with the melted glaciers that surround. Merzbacher Lake glacial flash flood occurred 62 times and more than 90% frequency in the period of 1932-2008. Glaciers melt and glacier flash floods play a vital role in runoff supply and flood control security for theAksu River and the Tarim River in China. Over the past years,the Tianshan have started melting down with the increase in temperature leading to formation of increasing number of glacier-fed lakes. The total discharge of glacier flash floods is increasing to 3×108～4×108m3in 1990s from 1×108m3of 1960s-1970s,and the total flood volumeis up to 4.5×108m3. The Peak discharge has increased 32% from 1950s to 1990s.Glacier flash floods drainage in Merzbacher Lake by the river way under the ice to downstreamand the flood period often lasted a few days to more than two weeks. The changes in glacier mass balance in the Kumarik River Basin have significantly influences on glacial flash flood,the more glacier melt,the larger the peak discharge. With climate warming,the pressure of flood control is increasing in the lower reaches of the Aksu River. Therefore,it is vital to strengthen the observation and monitoring of the glaciers and the water levels of glacial lake,establish early warning systems for the forecasting of glacial lake outburst flood and downstream security.