Contributing factors to ice mass loss on Himalayan debris-covered glaciers.

摘要

Despite being heavily covered in debris, glaciers of the Himalaya have undergone and continue to undergo major losses of ice volume. This 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 1 m/year. This dissertation makes use of cartographic, photographic, and field data from the Tibetan Plateau and Ngozumpa, one of Nepal's largest and longest glaciers, towards determining and quantifying factors that influence glacial ice loss in the high Himalaya.;Volume estimates, using historical maps and archival/modern-day expedition photos, show glacial loss of 3.7+/-0.6 cubic km total for four major glaciers in Tibet. Over 100-meter ice height losses are observed from lateral moraine to glacier surface in some locations. This is similar to the losses found in the southern (Nepalese) Himalaya, despite the smaller mean-illumination angle of glaciers flowing northward and the rain-shadow geographical setting.;The presence of supraglacial lakes can accelerate vertical ice mass loss. From time-lapse photography, small ponds in the mid-ablation zone on Ngozumpa were found to have different growth patterns: evaporation and/or infiltration of water through the underlying substrate; expansion through large calving events; and multiple fills, drains and refills, providing evidence for connections made to the englacial/subglacial system.;Lake floor deepening rate on Spillway, a large supraglacial lake on Ngozumpa, is important to quantify, as the lake's growth presents a flooding hazard to Sherpa villages down-valley. Sonar data provide detail on lake floor substrates, distinguishing mud, rock, and bare ice. In areas of fast deepening where low mean bottom temperatures prevail, thin debris cover or bare ice is encountered. This finding is consistent with previously reported localized regions of lake deepening, and is useful in predicting future growth.;Impurities in snow and ice at the higher altitudes can lead to decreases in albedo and, thus, accelerated melting in glacier accumulation zones. Snow samples were collected from 4800 - 6100 m.a.s.l. in valleys of eastern and western Nepal. Downwind of villages, black carbon was found to be the dominant contaminant, while for more remote glaciers further up-valley, dust prevails.