Factors controlling the accelerated expansion of Imja Lake, Mount Everest region, Nepal

This study explores the link between area increase of Imja Tsho (Lake) and changes of Imja Glacier (area similar to 25 km(2)) under the influence of climate change using multitemporal satellite imagery and local climate data. Between 1962 and 2013, Imja Lake expanded from 0.03 +/- 0.01 to 1.35 +/- 0.05 km(2) at a rate of 0.026 +/- 0.001 km(2) a(-1). The mean glacier-wide flow velocity was 37 +/- 30 m a(-1) during 1992-93 and 23 +/- 15 m a(-1) during 2013-14, indicating a decreasing velocity. A mean elevation change of -1.29 +/- 0.71 m a(-1) was observed over the lower part of the glacier in the period 2001-14, with a rate of -1.06 +/- 0.63 m a(-1) in 2001-08 and -1.56 +/- 0.80 m a(-1) in 2008-14. We conclude that the decrease in flow velocity is mainly associated with reduced accumulation due to a decrease in precipitation during the last few decades. Furthermore, glacier ablation has increased due to increasing maximum temperatures during the post-monsoon months. Decreased glacier flow velocities and increased mass losses induce the formation and subsequent expansion of glacial lakes under favourable topographic conditions.