Holocenemicroweathering rates and processes on ice-eroded bedrock,

Abstract: Post-glacial weathering of ice-eroded metamorphic bedrock was investigated in the Røldal area (608N) of the Hardangervidda Plateau in southern Norway. Quartz veins were used as reference surfaces to determine a mean post-glacial surface lowering rate of 0.55 mm ka21. Chemical characteristics of late-season runoff were determined for one catchment (Snøskar) and a chemical erosion rate of 4.9 t km22 a21 was obtained. A mean in situ fracture enlargement due to microweathering of 0.12 mm ka21 was also determined. These rates are low, although comparable with similar environments in cold regions, and suggest that microweathering has had relatively little impact on Holocene landscape evolution. Weathering rind thickness was found to be less on fracture walls than on exposed bedrock surfaces, suggesting fractures have not played a significant role in microweathering. Observations of weathering morphology reveal a range of forms including shallow spalling, tafoni and pseudokarren, indicating locally intense weathering activity. Analysis of interrelationships between multiple weathering indices points to the importance of bedrock microweathering as a precursor to macro-breakdown and landform evol-ution. The research reasserts the importance of chemical activity in cold environments and the importance of moisture supply for effective microweathering. Weathering of ice-eroded outcrops has the potential to significantly influence landscape evolution in periglacial environments during the post-glacial period. However, there has been relatively little work to determine rates of post-glacial bedrock weathering in cold environments. Traditionally, weathering in cold environments was seen to be the work of mechanical processes, specifically freeze–thaw (Tricart 1969), and low temperatures were thought to inhibit chemical weathering activity (e.g. Peltier 1950). However, in recent years there has been a major change of emphasis in studies of weathering in cold environments away from tra-ditional concepts to greater emphasis on the rol