Glaciation, erosion, and landscape evolution of Iceland

Stratigraphic and sedimentological studies indicate that Iceland has experienced over 20 glaciations during the last 4-5 Myr, in reasonable agreement with the number of glaciations reconstructed from the ∂¹⁸O record in deep-sea sediment. The pattern of glacial erosion was to a large part controlled by constructive volcanic processes resulting in increased topographic relief after 2.5 Myr. Between 2.5 and 0.5 Ma valleys up to 400 m deep were excavated into the Tertiary basalts of eastern and south Iceland with an average erosion rate of 10-20 cm ka^-1. During the last 0.5 million years rates of erosion increased to 50-175 cm ka^-1, with an additional 200 to over 1000 m of valley excavation. Previous estimates of the rate of landscape erosion during the Holocene vary widely, from 5 to 70,000 cm ka^-1. We present new studies that define the rates of landscape denudation during the major part of the Holocene (the last 10,200 years): one based on the Iceland shelf sediment record, the other from the sediment record in the glacier-fed lake, Hvítárvatn. Both studies indicate average Holocene erosion rates of about 5 cm ka^-1 similar to our erosion rate estimate for 4-5 Ma old strata that has not been subjected to regional glaciation.