Plucking enhanced beneath ice sheet margins: evidence from the Grampian Mountains, Scotland

David E. Sugden, Adrian M. Hall, William M. Phillips, Margaret A. Stewart

Research output: Contribution to journalArticlepeer-review

Abstract

Concentrations of boulders are a common feature of landscapes modified by former mid-latitude ice sheets. In many cases, the origin of the boulders can be traced in the up-ice direction to a cliff only tens to hundreds of metres distant. The implication is that a pulse of plucking and short boulder transport occurred beneath thin ice at the end of the last glacial cycle. Here we use a case study in granite bedrock in the Dee Valley, Scotland, to constrain theory and explore the factors involved in such a late phase of plucking. Plucking is influenced by ice velocity, hydrology, effective ice pressure, the extent of subglacial cavities and bedrock characteristics. The balance between these factors favours block removal beneath thin ice near a glacier margin. At Ripe Hill in the Dee Valley, a mean exposure age of 14.2 ka on blocks supports the view that the boulder train formed at the end of ice sheet glaciation. The late pulse of plucking was further enhanced by ice flowing obliquely across vertical joints and by fluctuations in sub-marginal meltwater conditions. An implication of the study is that there is the potential for a wave of ice-marginal plucking to sweep across a landscape as an ice sheet retreats.
Original languageEnglish
Pages (from-to)34-44
JournalGeografiska Annaler: Series A, Physical Geography
Volume101
Issue number1
Early online date22 Nov 2018
DOIs
Publication statusPublished - 2 Jan 2019

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