Post-glacial weathering and blockstream development in a periglacial environment, Hardangervidda, southern Norway

D. T. Nicholson*1, F. H. Nicholson2, F. Booth1 and J. J. Wildman1

*Corresponding author: Department of Environmental and Geographical Sciences, Manchester Metropolitan University, Chester Street, Manchester, UK. E-mail: d.nicholson@mmu.ac.uk Tel: +44 161 247 6232. 1Manchester Metropolitan University, 2Liverpool John Moores University

Abstract

This poster presents preliminary results of research on Hardangervidda in southern Norway to examine the role of weathering in landform evolution in a high altitude, mid-latitude, periglacial environment. This part of the plateau exhibits significant relief, including deep valleys, broad basins, and ubiquitous roche moutonnee and ice moulded ridges. The geology of the area is dominated by granitic composition metamorphics with some fine-grained meta-basic rocks. Ice-moulded outcrops of these rocks evidently resisted erosion by ice during the last period of glaciation. Even the highest surfaces display glacial scouring and moulding indicative of erosive, warm-based ice. This suggests that weathering features and blockstreams have developed since the last glacial period.

Most rock outcrops show clear evidence of ice-moulding and are usually surrounded by a mantle of apparently fresh, coarse, angular debris. This debris contains very little fine sediment and generally takes the form of blockstreams. There is clear downslope migration of boulder deposits due to solifluctive creep or slow gravitational creep or both. However, these blockstreams are being continually fed new material. The main contributing sources appear to be the macro-breakdown of intact rock in low-lying areas, mass movement (mainly rockfalls) from infrequent steep rock slopes and occasional rounded boulders which are probably glacially derived.

Many ice-moulded ridges and roche moutonnee, which have survived since the last glaciation, are being actively broken down by a combination of fracture enlargement (probably enhanced by chemical weathering) and frost shattering. In addition to gravitational forces, frost heave processes are also responsible for moving loose blocks away from their original source and into proximal blockstreams. One of the key objectives of this research is to examine the role of weathering in blockstream development and some of the lithological and topographic controls on weathering efficacy. One of the ways in which this is being achieved is by the determination of fracture spacing and other fracture characteristics on ice-moulded forms in contrasting lithologies. Results so far reveal a fracture index If (fractures per metre) ranging from 2.2 to 11.7 with banded granitic rocks being less intensely fractured (If = 2.2-4.2) than more basic and schistose rocks (If = 4.5-11.7).

A further objective of the research is to examine the influences on the spatial distribution of blockstreams in this region, particularly the role of slope angle, potential block source areas and lithology. A classification of blockstream characteristics in the region has been developed and used as the basis for mapping and analysing their spatial distribution.