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Effects of debris on ice-surface melting rates: an experimental study
- Natalya Reznichenko, Tim Davies, James Shulmeister, Mauri McSaveney
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- Journal:
- Journal of Glaciology / Volume 56 / Issue 197 / 2010
- Published online by Cambridge University Press:
- 08 September 2017, pp. 384-394
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Here we report a laboratory study of the effects of debris thickness, diurnally cyclic radiation and rainfall on melt rates beneath rock-avalanche debris and sand (representing typical highly permeable supraglacial debris). Under continuous, steady-state radiation, sand cover >50 mm thick delays the onset of ice-surface melting by >12 hours, but subsequent melting matches melt rates of a bare ice surface. Only when diurnal cycles of radiation are imposed does the debris reduce the longterm rate of ice melt beneath it. This is because debris >50 mm thick never reaches a steady-state heat flux, and heat acquired during the light part of the cycle is partially dissipated to the atmosphere during the nocturnal part of the cycle, thereby continuously reducing total heat flux to the ice surface underneath. The thicker the debris, the greater this effect. Rain advects heat from high-permeability supraglacial debris to the ice surface, thereby increasing ablation where thin, highly porous material covers the ice. In contrast, low-permeability rock-avalanche material slows water percolation, and heat transfer through the debris can cease when interstitial water freezes during the cold/night part of the cycle. This frozen interstitial water blocks heat advection to the ice–debris contact during the warm/day part of the cycle, thereby reducing overall ablation. The presence of metre-deep rock-avalanche debris over much of the ablation zone of a glacier can significantly affect the mass balance, and thus the motion, of a glacier. The length and thermal intensity of the diurnal cycle are important controls on ablation, and thus both geographical location and altitude significantly affect the impact of debris on glacial melting rates; the effect of debris cover is magnified at high altitude and in lower latitudes.
5 - Mobility of long-runout rock avalanches
- Edited by John J. Clague, Simon Fraser University, British Columbia, Douglas Stead, Simon Fraser University, British Columbia
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- Landslides
- Published online:
- 05 May 2013
- Print publication:
- 23 August 2012, pp 50-58
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Summary
Abstract In this chapter we address the conundrum of the surprisingly long runout of large rock avalanches, which has been the subject of many investigations since it was first recognized in the nineteenth century in Switzerland. After describing the nature of the problem quantitatively, we briefly outline the many explanations that have been put forward to explain it; we also describe the wide variety of circumstances in which long runout is known to occur. We then examine the ability of the proposed explanations to apply to this range of circumstances, in order to identify those explanations that can work in all the environments in which long runout occurs. The process of dynamic rock fragmentation appears to be the only mechanism that satisfies this criterion. We outline this mechanism and its energetics in more detail, and summarize its recent success in quantitatively explaining the 40 km runout and the morphological characteristics of the 25 km3 Socompa debris avalanche deposit in Chile.
Contributors
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- By Federico Agliardi, Andrea Alpiger, Gianluca Bianchi Fasani, Lars Harald Blikra, Brian D. Bornhold, Edward N. Bromhead, Marko H.K. Bulmer, D. Calvin Campbell, Marie Charrière, Masahiro Chigira, John J. Clague, John Coggan, Giovanni B. Crosta, Tim Davies, Marc-Henri Derron, Mark Diederichs, Erik Eberhardt, Carlo Esposito, Robin Fell, Paolo Frattini, Corey R. Froese, Monica Ghirotti, Valentin Gischig, James S. Griffiths, Stephen R. Hencher, Reginald L. Hermanns, Kris Holm, Seyyedmahdi Hosseyni, Niels Hovius, Christian Huggel, Florian Humair, Oldrich Hungr, D. Jean Hutchinson, Michel Jaboyedoff, Matthias Jakob, Julien Jakubowski, Randall W. Jibson, Katherine S. Kalenchuk, Nikolay Khabarov, Oliver Korup, Luca Lenti, Serge Leroueil, Simon Loew, Oddvar Longva, Patrick MacGregor, Andrew W. Malone, Salvatore Martino, Scott McDougall, Mika McKinnon, Mauri McSaveney, Patrick Meunier, Dennis Moore, Jeffrey R. Moore, David C. Mosher, Michael Obersteiner, Lucio Olivares, Thierry Oppikofer, Luca Pagano, Massimo Pecci, Andrea Pedrazzini, David Petley, Luciano Picarelli, David J.W. Piper, John Psutka, Nicholas J. Roberts, Gabriele Scarascia Mugnozza, David Stapledon, Douglas Stead, Richard E. Thomson, Paolo Tommasi, J. Kenneth Torrance, Nobuyuki Torii, Gianfranco Urciuoli, Gonghui Wang, Christopher F. Waythomas, Malcolm Whitworth, Heike Willenberg, Xiyong Wu
- Edited by John J. Clague, Simon Fraser University, British Columbia, Douglas Stead, Simon Fraser University, British Columbia
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- Book:
- Landslides
- Published online:
- 05 May 2013
- Print publication:
- 23 August 2012, pp vii-x
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- Export citation