Hydrological and thermal regimes in a supraglacial lake: Imja, Khumbu, Nepal Himalaya

Supraglacial Imja Lake (lake level, 5010 m a.m.s.l.), Khumbu, Nepal Himalay a, has increased its size on the tongue of Imja Glacier since the 1950s. In order to clarify the mechanism of the lake expansion, the physical conditi ons, water budget and heal budget of the lake were examined by measuring wa ter temperature, water turbidity, lake level, meteorology and water dischar ge. These measurements were carried out in the monsoon season of July 1997, when the glacier melt occurred in the ablation area with air temperature o f more than 0 degrees C. Density stratification in the lake is built up by an effect of water pressure on lake water, but, neglecting the effect, lake water density is defined by suspended sediment concentration rather than t emperature. Glacier-melt water from the subaqueous part of the glacier term inus mixed with lake surface water of 4-8 degrees C, and diffused the water of about 3 degrees C into the deeper zone of the lake. This advective, the rmal diffusion occurs by sediment-laden underflow and relatively clear dens ity interflow. The sediment-laden underflow is induced by intermittent glac ier-melt sediment discharge at the terminus, while the density interflow is probably produced by continuous glacier-melt water discharge. Calculation of water budget of the lake indicates that meltwater inflow at the glacier terminus and surface water outflow at the outlet determine the hydrological conditions of the lake. The net heat transfer by melting of the terminal i ce and dead ice, connected to the lake expansion, was evaluated by calculat ing the heat budget of the lake.