La mesure de l'érosion des glaciers tempérés : Essai de synthèse / Measuring the erosion of temperate glaciers : a synthesis

Abstract

Abstract : The tapping of subglacial water and the observation of deglaciated areas makes it possible, through a comparison of known situations and recorded results, to draw a certain number of conclusions regarding the erosion of temperate glaciers which can be divided into three major groups : 1. Subglacial erosion frequently provides the most visible traces of the work of glaciers, even if their abrasive action remains the most original testimony of the glacial landscape. The effects of subglacial erosion can be grouped into three classes : stream glosses, subglacial channels and subglacial gorges. 2. Abrasion and associated plucking can be considered as the main forms of erosion resulting from glacier movement. The intensity of abrasion depends on the number of rock inclusions which, entrained by the glacier, reach the bed and, more particularly, on those inclusions which remain in contact with the bed. Abrasion also varies as a function of the rate of replacement of abrading material, in other words as a function of the glacier's velocity. Fi- nally, abrasion is also conditioned by the nature of the entrained rocks themselves. At the sides of the glacier, subglacial morainic material is more abundant, larger and more heterogeneous, so that the effects of abrasion, in the form of striations, polishing and scraping, are at a maximum there. 3. Proglacial gouging is the third process by which a glacial erodes. It is a result of the transporting power of the glacier, as rock fragments lying in its path are pushed along in front of it. Erosion of the rock substrate is not proportional to the intensity but rather to the frequency of fluctuations in the glacier. Proglacial gouging is most effective during the incipient phase of glaciation and at flat marginal sites where the mobility of the glacier is greatest.