A reconstruction of the last glacial maximum (LGM) ice-surface geometry in the western Swiss Alps and contiguous Alpine regions in Italy and France

Abstract

A reconstruction of the last glacial maximum (LGM) ice-surface geometry in the western Swiss Alps and contiguous Alpine regions in Italy and France is based on detailed field mapping of glacial trimlines, ice-erosional features and periglacial forms. Field data provide evidence of LGM ice-surface elevations and ice-flow directions. The LGM ice surface is portrayed as a grid-format digital elevation model (DEM) using geographic information system (GIS) software. LGM ice-surface areas and ice volumes in selected regions are calculated using a DEM of the present land topography. The reconstruction described in this paper is presented in conjunction with a previously determined LGM ice-surface reconstruction for the central and eastern Swiss Alps. The LGM ice cap in the western Swiss Alps and contiguous Alpine regions in Italy and France was characterized by transection glaciers. Four main centers of ice accumulation that influenced the transection glaciers include the Rhône ice dome, the Aletsch icefield, the southern Valais icefield, and the Mt. Blanc region. Major ice diffluences were located north of Simplon Pass, on Gd. St. Bernard Pass and north of present-day Glacier d’Argentière. Estimates of LGM ice volumes in selected regions show that the largest input of ice into the Rhône Valley was from the southern Valais icefield. Centered in the southern Mattertal, the LGM southern Valais icefield had a surface elevation of at least 3010 m and an ice thickness of at least 1400 m. The LGM ice-surface reconstruction and calculated ice volumes for selected regions are the basis for a hypothesis as to how erratic boulders from the southern Valais and Mt. Blanc regions were transported to the northern Alpine foreland. Certain LGM centers of ice accumulation and ice-flow directions presented in this paper are also examined for possible paleo-atmospheric circulation information.