Rapid Holocene chemical weathering on a calcitic lake shoreline in an alpine periglacial environment: Attgløyma, Sognefjell, southern Norway

Abstract

AbstractA small lake (Attgløyma) at an altitude of about 1220 m in the low‐alpine zone, southern Norway, has a shore platform in calcitic and quartzitic muscovite‐chlorite schists. The platform has recently been exposed by a fall in lake level due to upstream dam construction and exhibits micro‐landforms ranging from pits and grooves to upstanding crenulate ridges produced by differential chemical weathering under relatively constant conditions over the last ca. 10 000 years. The maximum surface lowering rate of the calcitic layers estimated from differential weathering is 35 mm ka−1, which is about an order of magnitude greater than most previous estimates from alpine and polar periglacial environments. Average bedrock surface lowering across the whole platform reached a maximum of 15.5 ± 2.2 mm ka−1 in a vertical zone corresponding with the former lake level, declining to negligible values around 0.7 m below lake level. Differential weathering and bedrock surface lowering were also negligible immediately above lake level. Correspondence of maximum surface lowering rates with the former lake level and a shoreline notch at the back of a platform suggest that the effects of solutional weathering of the calcite have been enhanced by water movement generated by small lake‐surface waves. Copyright © 2006 John Wiley & Sons, Ltd.