Glacial Flooding & Disaster Risk Management Knowledge Exchange and Field Training July 11-24, 2013 in Huaraz, Peru HighMountains.org/workshop/peru-2013
Rates of Change on Spillway Lake, Ngozumpa Glacier, Nepal Ulyana N. Horodyskyj University of Colorado, Boulder Introduction: Through a combination of modern satellite imagery, repeat photography from the 1950s, and on-‐going field measurements, we know that glaciers of the Mt. Everest and Cho Oyu regions in Nepal have undergone and continue to undergo major losses of ice volume (e.g., Thompson et al., 2012; Bolch et al., 2008). This volume loss occurs not so much by loss of area, but more from a reduction in the thickness of the glacier at average rates that locally can exceed 1m/year. The formation of supraglacial (surface) lakes appears to be the catalyst for this loss; once formed, these lake basins can grow and migrate by back wasting and calving of surrounding ice walls (e.g., Byers 2007; Sakai et al. 2002; Benn et al. 2001; Benn et al. 2000). Fill and drain events in these basins throughout the summer, triggered either by monsoonal precipitation and/or englacial conduit flooding, can accelerate the melt as more ice, previously covered up by debris, is “cleaned off” by the drainage of water, thus exposing more ice to solar radiation (Horodyskyj et al., in progress). An important concern is whether lake formation itself is accelerating. To this end, Spillway Lake, a large supraglacial base-‐level lake on Ngozumpa, one of Nepal’s longest glaciers, (Fig. 1), has been profiled by researchers at the University of St. Andrews and Swansea University (2001/2009). Interpolated point bathymetry maps, made with a simple depth sounder (Fig. 2) revealed where parts of the lake were deepening, sometimes upwards of 13 m/yr (e.g., Thompson et al. 2012). The lake may eventually pose a flooding hazard to Sherpa villages down-‐glacier, hence the importance in quantifying the physics responsible for deepening and growth.