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

Abstract

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).