Medial Moraines of the Haut Glacier D’arolla, Valais, Switzerland: Debris Supply and Implications For Moraine Formation

Abstract

ABSTRACT. The Haut Glacier d' Arolla displays three medial moraines: an ablation-dominant moraine east of the glacier centre line, an ice-stream interaction moraine west of the glacier centre line, and a medial-lateral supraglacial moraine complex along the western margin of the glacier. The eastern moraine is formed by the emergence of coarse angular clasts from a series of short longitudinal debris bands 1 km from the glacier terminus; this debris is derived from rock falls at the glacier head-wall, and follows a low-level transport path through the glacier. The western moraine is formed partly by the direct fall of weathered debris on to the ice surface at a point 2.6 km from the snout, but it receives further increments of sediment from extensive longitudinal en glacial debris bands developed from the convergence of two ice streams with lateral englacial debris septa. The medial-lateral moraine complex is formed largely by rock falls from the western valley wall, but is also nourished by a debris layer developed at the base of the small tributary Glacier de la Mitre. This layer crops out at the eastern margin of the re-sultant inset ice stream, and releases more rounded, abraded and comminuted rock fragments to supplement the surface debris cover of supraglacial origin. RESUME.

Debris transport in a temperate valley glacier: Haut Glacier d’Arolla, Valais, Switzerland

“…Previous authors (Small and others, 1979;Gomez and Small, 1985;Small, 1987) suggested that the eastern medial moraine is formed by the emergence of coarse angular clasts from a series of short longitudinal debris bands, identical to the debris emerging along planes of primary stratification described here. Introducing the concept of folding of rockfall-bearing primary stratification into the hypothesis of medial moraine formation explains the intermittent nature of the moraine lenses and the V-shape of some moraines (noted in Fig.…”

“…Mair and others, 2001), and the development of high-resolution glacier flow modelling (Hubbard and others, 1998;Hubbard and Hubbard, 2000). The formation of medial moraines and sediment transport pathways have also been described at the glacier (Small and others, 1979;Gomez and Small, 1985;Small, 1987).…”

“…The medial moraines of Haut Glacier d'Arolla were investigated by Small and others (1979), Gomez and Small (1985) and Small (1987) when the glacier was considerably larger.…”

“…Direct rockfall from La Vierge is the main source of debris forming the moraine (cf. Gomez and Small, 1985). Rockfall debris which has been deformed within the ice is concentrated at the flow unit boundary between the main glacier tongue and the La Vierge tributary.…”

The Structural Glaciology of a Temperate Valley Glacier: Haut Glacier d'Arolla, Valais, Switzerland

“…Haut Glacier d'Arolla is a north-flowing valley glacier at the southern end of the Arolla valley, which forms the western branch of There is a substantial literature on many aspects of Haut Glacier d'Arolla, for example sediment transfer (e.g., Gomez and Small, 1985;Small, 1987), glacial melt-water chemistry (e.g., Brown et al, 1994), glacier geometry (Sharp et al, 1993), subglacial hydrology (e.g., Hubbard et al, 1995;Nienow et al, 1998), interactions between glacier hydrology and dynamics (e.g., Mair et al, 2001), and highresolution glacier flow modeling Hubbard and Hubbard, 2000).…”