Ice ablation and meteorological conditions on the debris-covered area of Baltoro glacier, Karakoram, Pakistan

Abstract

During the recent Italian expedition ‘K2 2004 – 50 years later’ (June–July 2004) on Baltoro glacier, Karakoram, Pakistan, glaciological field experiments were carried out on the debris-covered area of this high-elevation glacier. The aim was to investigate the ice ablation and its relations with debris thermal properties and meteorological conditions. Ablation measurements along the glacier up to about 5000 m and within a dedicated test field were combined with meteorological data from two automatic weather stations located at Urdukas (4022 ma.s.l.) and at K2 Base Camp (5033 m a.s.l.). In addition, temperature measurements of the debris cover at different depth levels along the glacier allowed the calculation of debris surface temperature and of the debris thermal resistance (R). Using the air temperature, the local mean lapse rate (0.0075˚C m−1) and the measured ablation, the degree-day factors (K) at different locations on the glacier were calculated. The ice ablation rates were related to debris thickness and elevation. They are typically on the order of 4 cm d−1 during the observation period. However, it was found that the surface topography (slope, aspect) has an influence on the total ablation similar to that of the debris thickness. Thermal resistance of the debris cover and its distribution over the glacier were estimated. Finally, a best-guess estimate of the total meltwater production was calculated from available climate data.

A comparison of glacier melt on debris-covered glaciers in the northern and southern Caucasus

“…Similar observations were made in other, longer measurements (e.g. Mihalcea et al, 2006;Konovalov, 2000). After a maximum in melt, the melt rate decreases and reaches the same magnitude as for clear ice at the critical debris thickness of about 2 cm for Zopkhito glacier and 3 cm for Djankuat glacier.…”

“…10) shows that the measurements in the Caucasus provide factors in a similar range as in the Karakoram (Mihalcea et al, 2006) and the Tian Shan (Hagg et al, 2008). For thin debris layers, however, the variation of the factors is large and between the regions, melt rates can vary by a factor three.…”

“…Melt rates of the debris-covered glaciers, however, vary considerably due to different factors, for example, thermal properties of the supra-glacial debris cover (Nakawo and Young, 1981). Dedicated process studies were carried out focusing on the thermal conditions of the sub-debris ice melt (Brock et al, 2007;Mihalcea et al 2006; Published by Copernicus Publications on behalf of the European Geosciences Union.…”

Impact of debris cover on glacier ablation and atmosphere–glacier feedbacks in the Karakoram

“…For example, Nicholson and Benn (2012) reported very heterogeneous debris thicknesses on the Ngozumpa glacier, Nepal, varying between 0.5 and 2.0 m over distances of less than 100 m. Spatial variability arises from many factors, including hillslope fluxes to the glacier; surface and subsurface transport and, the presence of ice cliffs, melt ponds and crevasses (e.g., Brock et al, 2010;Zhang et al, 2011). The few available field measurements do not support a relationship between debris thickness and elevation (e.g., Mihalcea et al, 2006;Reid et al, 2012). However, measurements on the Tibetan Plateau (Zhang et al, 2011) in Nepal (Nicholson and Benn, 2012), and in the Karakoram (Mihalcea et al, 2008a) indicate that thicker values are more prevalent near glacier termini, while thinner ones are more ubiquitous up-glacier.…”

“…The region has received a great deal of public and scientific attention in recent years due to evidence of stable or even slightly positive mass balances in the 2000s (Hewitt, 2005;Scherler et al, 2011;Gardelle et al, 2012Gardelle et al, , 2013Kääb et al, 2012) that are in contrast with predominantly negative balances of glaciers in the rest of the Hindu-Kush Himalaya (HKH; Cogley, 2011) Knowledge of the hydrological response of Karakoram glaciers to climate change is critical, since their meltwater contributes to freshwater resources in this highly populated region of South Asia (Kaser et al, 2010;Lutz et al, 2014). However, due to logistical constraints and political instability, field observations of glaciological and meteorological conditions in the Karakoram are sparse in space and time, in particular at high altitudes (Mihalcea et al, 2006(Mihalcea et al, , 2008aMayer et al, 2014). Although observational records have been supplemented in recent decades by remote-sensing data (e.g., Gardelle et al, 2012Gardelle et al, , 2013Kääb et al, 2012), large gaps remain in our understanding of the important drivers of glacier change in this region, including regional atmospheric conditions, local topography and glacier debris cover, as well as interactions between them.…”