Annually resolved events of Younger Dryas glaciation in Lochaber (Glen Roy and Glen Spean), western Scottish Highlands

Abstract

AbstractThis paper presents the results of micromorphological analysis of laminated sediments that accumulated in ice‐dammed lakes in Lochaber (Glen Roy and vicinity) during the Younger Dryas (Loch Lomond) Stadial. These lakes were responsible for the formation of the famous ‘Parallel Roads of Glen Roy’ (Agassiz, 1840), prominent shorelines cut into the valley sides of Glen Roy and adjacent valleys. Annually deposited (varved) layers, which can be distinguished from other rhythmites by micromorphological examination, have enabled the construction of a varve chronology which underpins the glacial history of the region, the duration of the lake stands and rates of ice margin advance and retreat. The lake system existed for a total of 515 a. During a rise in lake levels, the lowermost (260 m), middle (325 m) and highest (350 m) lakes existed for minimal periods of 191, 112 and 116 a, respectively, and the fall of lake levels from 350 m to 260 m took 95 years. Ice advance rates of between 13.4 and 41.9 m a−1 are inferred, while ice retreat is estimated to have been ∼38.5 m a−1. A provisional correlation between the Lochaber varve and GRIP ice core records suggests that the lakes started to form at ca. 12 165 a BP, in turn implying that the Loch Lomond Readvance limits in this area were not achieved until late in the Younger Dryas interval, a conclusion which does not accord with that based on numerical model simulations. Copyright © 2010 John Wiley & Sons, Ltd.