Boulder weathering processes at the margins of perennial snowpatches

D. T. Nicholson

Department of Environmental and Geographical Sciences, Manchester Metropolitan University, Chester Street, Manchester, UK. E-mail: Tel: +44 161 247 6232.

Poster abstract

It is generally accepted that rock weathering is enhanced at the margins of late-lying and perennial snowpatches. However, uncertainty remains over the nature of the weathering processes involved and also on factors controlling spatial variability. Three complementary indices of weathering were quantified along boulder transects at the margins of two snowpatch sites on Hardangervidda in southern Norway. With increasing distance from the snow core (late summer snowpatch) both weathering rind thickness (WRT) and the proportion of fractured boulders show a significant reduction and rock surface hardness (determined from Schmidt hammer rebound) shows a steady increase. When comparing snow margins with snow-free control sites, WRT shows a four-fold increase and there is a three to four-fold increase in the proportion of fractured boulders. A significant inverse correlation was found between WRT and rock surface hardness and these properties may be inter-dependent. The findings verify the role of snow-cover in enhancing rock weathering and underline the importance of chemical weathering in cold environments. However, both chemical and mechanical processes are invoked at a variety of scales. While moisture availability may be the primary control on spatial variability in weathering indices, other factors are invoked including micro-topographic variability and the downslope movement of sediment.