Ice structure and dynamics of the Jumeaux Glacier (Valtournanche, Aosta Valley, Italy)

Abstract

This paper describes the type of ice and the dynamics of the Jumeaux Glacier, a conical glacier entirely situated below the snowline and supplied by avalanches. Examination of its structure from the rocky substrate to the surface thanks to the presence of an accessible subterranean stream net has shown that it is mainly composed of firn nearly transformed into infiltration ice with interbeddings of conglomeratic ice derived from the collapse of seracs forming at the tip of the cone. Cave ice and infiltration ice fillings are also present in gaping tension fractures, as well as debris-containing ice underlying compressive structures similar to overthrusts that are a feature of the lower half of the glacier. The presence of recrystallization ice, crevasses and overthrust structures shows that this is a true glacier, despite its tiny extent, while the distribution of the recrystallization ice and direct observation indicate that the ice layers in the abrasion zone move like thin sheets sliding over each other: the inner structure is thus totally different from that of corrie glaciers, and displays similarities to that of some tongues of regenerated ice in the large Alpine glaciers. A computerised avalanche dynamics model elaborated from the parameter values derived from direct observation of landslide debris was used to examine the glacier’s supply processes. The conclusion is drawn that the main avalanches come to a stop below the glacier and only leave debris at irregularities in the terrain, such as bergschrunds, crevasses and terminal moraines, whose frequency and distribution are thus decisive. The glacier, therefore, is also very different from corrie glaciers in its replenishment pattern, since it lacks a true supply zone.