Backwasting rate on debris-covered Koxkar glacier, Tuomuer mountain, China

Abstract

A physically based energy-balance model with improved parameterization of solar radiation for a sloped ice surface has been developed to estimate the backwasting rate of an ice cliff in a debris-covered area. The model has been tested against observations between 5 August and 5 September 2008 on 38 ice cliffs in the debris-covered area of Koxkar glacier, Tuomuer mountain, China. We calculated that the energy-balance model gave a good estimate of the backwasting rates, with errors in the range ±1.96 cm d−1 and root-mean-square errors of 0.99 cm d−1. Errors arising from setting of surface albedo and turbulent flux parameterization were limited. We found that shortwave radiation is the most important heat source for ice-cliff ablation, contributing about 76% of the total heat available for ice melt, while the sensible heat flux provides nearly 24% of the total heat for ice-cliff wastage. The latent heat flux and net longwave radiation are comparatively small according to the model calculation. The mean backwasting rate of ice cliffs in the debris-covered area of Koxkar glacier is estimated at 7.64 m a−1 when the winter ablation is neglected. With this annual backwasting rate and given a mean slope angle of 46.4°, the backwasting of ice cliffs produces about 1.60 × 106 m3 of meltwater, accounting for about 7.3% of the total melt runoff from the debris-covered area.

Quantification of the ice-cored moraines' short-term dynamics in the high-Arctic glaciers Ebbabreen and Ragnarbreen, Petuniabukta, Svalbard

“…Moreover, our data showed that the transformations even within one moraine complex were not uniform in time and space, and that the sites which are active in one season can be almost completely stable in the next. To sum up, the results from Ebbabreen and Ragnarbreen are higher than previously reported from Svalbard, and are also higher than or of similar magnitude to the values reported from different climatic zones such as Iceland, the Himalayas and the European Alps (Krüger and Kjaer, 2000;Benn et al, 2001;Kjaer and Krüger, 2001;Han et al, 2010;Pelfini et al, 2012). Together with the evidently high local variability in dead-ice melting and sediment redisposition, it confirms the suggestion of Schomacker (2008) that these processes are more related to local factors such as topography and abundance of meltwater than climatic conditions.…”

Automated detection of ice cliffs within supraglacial debris cover

“…The importance of ice cliffs has become increasingly clear (Sakai et al, 1998;Han et al, 2010;Sakai et al, 2002;Watson et al, 2017), but the mapping of these features remains a challenge, especially at spatial scales beyond a few glaciers. The map-view surface expression of an ice cliff is often a crescent, circular or linear swath of steep, bare (or thinly debris-covered) glacier ice surrounded by a debris layer.…”

“…The mechanism(s) of ice cliff formation, the controls of ice cliff migration patterns and ice cliff residence time on a glacier are gaining research attention but are still poorly understood processes, in part, due to a lack of base data (Reid and Brock, 2014;Watson et al, 2017). Melt and surface energy fluxes at specific ice cliffs have been studied in detail (Sakai et al, 1998;Han et al, 2010;Sakai et al, 2002;Reid and Brock, 2014;Buri et al, 2016a) and digital elevation model (DEM) differencing has shown the spatial trends of enhanced glacier melt relative to surrounding debris cover and ice cliff evolution at the scale of several cliffs or a single glacier tongue (Thompson et al, 2016;Brun et al, 2016). All of the studies mentioned suggest that ice cliffs, if present on a debris-covered glacier, need to be accounted for in order to adequately model glacier mass loss and response to climate.…”

“…To the knowledge of the authors, five methods have been used to map ice cliffs: (1) field mapping (e.g., Steiner et al, 2015); (2) manual digitization from remote sensing data (e.g., Sakai et al, 1998;Han et al, 2010;Thompson et al, 2016;Watson et al, 2017); (3) automatically using a surface slope threshold (e.g., Reid and Brock, 2014); (4) automatically by principal component analysis using visible nearinfrared and shortwave infrared satellite bands (Racoviteanu and Williams, 2012); and (5) automatically by object based image analysis of unmanned aerial vehicle data . None of the remote sensing studies listed offer a confidence metric based on independent data for their ice cliff map products and field mapping is not realistic for large-scale analyses.…”

Climate–Glacier Dynamics and Topographic Forcing in the Karakoram Himalaya: Concepts, Issues and Research Directions

“…The presence of ice cliffs and supraglacial lakes are another unique characteristic of glaciers ( Figures 5 and 6) as both of these features are associated with high-magnitude ablation, and ice cliffs contribute considerably to the overall ablation of a glacier even though they often cover only a small percentage of the glacier surface [120,[134][135][136][137]. Theoretically, these features and glacier ablation form a positive feedback loop-an ice cliff exposes clean ice while supraglacial lakes exhibit low albedo both of which increase ablation.…”