A MECHANISM OF BASAL ICE-LAYER FORMATION INVOLVING MAJOR ICE-FABRIC CHANGES

ABSTRACT. An opportunity to analyse the mechanism for the formation of a basal ice layer was provided by Glacier de Tsanfleuron in the Swiss Alps. This glacier has some lateral subglacial cavities in which a basal ice layer forms on the bedrock floor and is subsequently incorporated at the base of the glacier. Petrographic and crystallographic analyses of the different types of ice have provided a means of investigating the successive stages of the process. These analyses show major structural changes which provide field confirmation of the deformation mechanisms studied by several authors in laboratory experiments