Articles | Volume 12, issue 9
Nat. Hazards Earth Syst. Sci., 12, 2977–2991, 2012
Nat. Hazards Earth Syst. Sci., 12, 2977–2991, 2012

Research article 27 Sep 2012

Research article | 27 Sep 2012

Instabilities on Alpine temperate glaciers: new insights arising from the numerical modelling of Allalingletscher (Valais, Switzerland)

J. Faillettaz1,*, M. Funk1, and D. Sornette2 J. Faillettaz et al.
  • 1Laboratory of Hydraulics, Hydrology and Glaciology (VAW), ETH Zürich, 8092 Zürich, Switzerland
  • 2Department of Management, Technology and Economics, ETH Zürich, 8092 Zürich, Switzerland
  • *now at: Soil and Terrestrial Environmental Physics (STEP), ETH Zürich, 8092 Zürich, Switzerland

Abstract. The processes leading to a glacier instability depend on the thermal properties of the contact between the glacier and its bedrock. Assessing the stability of temperate glacier (i.e. the glacier can slide on its bedrock) remains problematic. In order to scrutinize in more detail the processes governing such "sliding" instabilities, a numerical model designed to investigate gravitational instabilities in heterogeneous media was further developed to account for the presence of water at the interface between the bedrock and the glacier for Allalingletscher. This model made it possible to account for various geometric configurations, interaction between sliding and tension cracking and water flow at the bedrock. We could show that both a critical geometrical configuration of the glacier tongue and the existence of a distributed subglacial drainage network were the main causes of the Allalingletscher catastrophic break-off. Moreover, the analysis of the modelling results diagnosed the phenomenon of recoupling of the glacier to its bed followed by a pulse of subglacial water flow as a potential new precursory sign of the final break-off in 1965. This model casts a gleam of hope for a better understanding of the ultimate rupture process resulting from such glacier sliding instabilities.