Articles | Volume 72, issue 4
Geogr. Helv., 72, 421–442, 2017
Geogr. Helv., 72, 421–442, 2017

Standard article 07 Dec 2017

Standard article | 07 Dec 2017

A study of the Würm glaciation focused on the Valais region (Alps)

Patrick Becker1, Martin Funk1, Christian Schlüchter2, and Kolumban Hutter1 Patrick Becker et al.
  • 1Veruschsanstalt für Wasserbau, Hydrologie und Glaziologie, ETH Zürich, Zürich, 8093, Switzerland
  • 2Institut für Geologie, Universität Bern, Bern, 3012, Switzerland

Abstract. During the Last Glacial Maximum (LGM), the glaciation in the European Alps reached maximum ice extent. We already simulated the steady states of the Alpine ice coverage for several climate drivers in Becker et al. (2016) and heighten in this article such studies for the Swiss Valais region. To this end, we employ the Parallel Ice Sheet Model (PISM), which combines the shallow ice approximation (SIA) with basal sliding elements of the shallow shelf approximation (SSA), and subject this model to various external driving mechanisms. We further test the sensitivity of this kind of the ice coverage in the Valais region to a temporally constant climate and to monotonic ice sheet build-up from inception to steady state as well as to the Dye 3 temperature driving during the past 120 000 years. We also test differences in the precipitation patterns exerted to the northern and southern catchment areas of the Rhone and Toce rivers to possible transfluence changes in ice from the northern to the southern catchment areas and vice versa. Moreover, we study the effect of the ice deformability and estimate the removal up to 1000 m of sediment in the Rhone Valley and study the removal of rock hindering the flow through the valley cross section at the knee of Martigny. All these studies took place because of a discrepancy in the ice height prediction of the modelled ice sheet with its geomorphologically reconstructed counterpart with proxy data obtained by Bini et al. (2009) as well as a difference in ice height between the two of up to 800 m. Unfortunately, all the scenarios in the model do not sufficiently reduce this discrepancy in the height prediction and the geomorphological reconstruction. The model results have discovered an ice dynamical discrepancy with the land map in Bini et al. (2009).

Short summary
This article studies the ice flow in the Valais region during the last glaciation (Würm) in detail. The numerical modelling shows a discrepancy of the height of the ice cap compared to the geomorphological evidence based on trimlines. However, geomorphological evidence at the Simplon Pass indicating an ice flow from the Rhone valley into the valley of Toce was confirmed. Furthermore it is shown that for this confirmation a sufficient ice thickness is obligatory.