The supraglacial debris system at the Pasterze Glacier, Austria: Spatial distribution, characteristics and transport of debris

摘要

This paper discusses spatial distribution, characteristics and transport of the supraglacial debris cover at Pasterze Glacier, Austria (c. 17.6 km(2), 47 degrees 05'N, 12 degrees 44'E). Research is based on field work, laboratory analyses, long-term monitoring data as well as semi-historic maps and orthophotos. The south-western part of the 3.6 km(2) large glacier tongue is mantled by a pronounced debris cover (1.2 km(2)). The total debris-covered area has increased by 0.8 km(2) during the last 38 years. Thicknesses of the debris cover increase significantly towards the glacier margin. Mean debris thickness along a longitudinal profile follows a power function decreasing from 47.3 cm close to the glacier terminus to 7.5 cm 3.8 km up-glacier. Sedimentological analyses of debris characteristics along a longitudinal profile revealed a tendency towards more slabby clasts and finer sediments further down-glacier attributed presumably to increased exposure to weathering. The mean annual debris load for the period 2001-2006 varied between 895 t.a(-1) close to the terminus, 1025 t.a(-1) at the central part and 745 t.a(-1) at the upper part of the glacier tongue. During the period 1970-2006 the efficiency of supraglacial debris transport was up to sixfold reduced due to decreased velocities. It is likely that Pasterze Glacier will continue to transform from a 'clean' glacier into a debris-covered glacier and finally into an ice-cored moraine: a presumably typical fate for comparable alpine valley glaciers caused by ongoing climate warming and subsequent glacier shrinkage.