30 Nov 2017
 | 30 Nov 2017
Status: this preprint was under review for the journal TC but the revision was not accepted.

Multiannual observations and modelling of seasonal thermal profiles through supraglacial debris in the Central Himalaya

Ann V. Rowan, Lindsey Nicholson, Emily Collier, Duncan J. Quincey, Morgan J. Gibson, Patrick Wagnon, David R. Rounce, Sarah S. Thompson, Owen King, C. Scott Watson, Tristram D. L. Irvine-Fynn, and Neil F. Glasser

Abstract. Many glaciers in the Central Himalaya are covered with rock debris that modifies the transfer of heat from the atmosphere to the underlying ice. These debris-covered glaciers are experiencing rapid mass loss at rates that have accelerated during the last two decades. Quantifying recent and future glacier mass change requires understanding the relationship between debris thickness and ablation particularly through the summer monsoon season. We present air, near-surface and debris temperatures measured during three monsoon seasons at five sites on Khumbu Glacier in Nepal, and compare these results to similar measurements from two other debris-covered glaciers in this region. Seasonal debris temperature profiles are approximately linear and consistent between sites for thick (> 0.5 m) and thin (< 0.5 m) debris across thicknesses ranging from 0.26 to 2.0 m. The similarities between these multiannual data imply that they are representative of supraglacial debris layers in the monsoon-influenced Himalaya more generally. We compare three methods to calculate sub-debris ablation, including using our temperature measurements with a thermal diffusion model that incorporates a simplified treatment of debris moisture. Estimated ablation between 3 June and 11 October at around 5000 m above sea level ranged from 0.10 m water equivalent beneath 1.5 m of debris to 0.47 m water equivalent beneath 0.3 m debris. However, these values are small when compared to remotely observed rates of surface lowering, suggesting that mass loss from these debris-covered glaciers is greatly enhanced by supraglacial and englacial processes that locally amplify ablation.

Ann V. Rowan et al.

Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Ann V. Rowan et al.

Data sets

Supraglacial debris temperatures, near-surface temperatures and on-glacier air temperatures measured during the 2014, 2015 and 2016 monsoon seasons at Khumbu Glacier, Nepal A. V. Rowan, D. J. Quincey, M. J. Gibson, and T. D. L. Irvine-Fynn

Ann V. Rowan et al.


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Short summary
Many glaciers in the Himalaya are covered with thick layers of rock debris that acts as an insulating blanket and so reduces melting of the underlying ice. Little is known about how melt beneath supraglacial debris varies across glaciers and through the monsoon season. We measured debris temperatures across three glaciers and several years to investigate seasonal trends, and found that sub-debris ice melt can be predicted using a temperature–depth relationship with surface temperature data.