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Progressive formation of modern drumlins at Múlajökull, Iceland: stratigraphical and morphological evidence

Journal article
Authors Ívar Örn Benediktsson
Sverrir A. Jónsson
Anders Schomacker
Mark D. Johnson
Ólafur Ingólfsson
Lucas Zoet
Neal R. Iverson
Johann Stötter
Published in Boreas
Volume 45
Pages 567-583
ISSN 0300-9483
Publication year 2016
Published at Department of Earth Sciences
Pages 567-583
Language en
Links doi.org/10.1111/bor.12195
Subject categories Geology

Abstract

© 2016 Collegium Boreas. Published by John Wiley & Sons Ltd The drumlin field at Múlajökull, Iceland, is considered to be an active field in that partly and fully ice-covered drumlins are being shaped by the current glacier regime. We test the hypothesis that the drumlins form by a combination of erosion and deposition during successive surge cycles. We mapped and measured 143 drumlins and studied their stratigraphy in four exposures. All exposures reveal several till units where the youngest till commonly truncates older tills on the drumlin flanks and proximal slope. Drumlins inside a 1992 moraine are relatively long and narrow whereas drumlins outside the moraine are wider and shorter. A conceptual model suggests that radial crevasses create spatial heterogeneity in normal stress on the bed so that deposition is favoured beneath crevasses and erosion in adjacent areas. Consequently, the crevasse pattern of the glacier controls the location of proto-drumlins. A feedback mechanism leads to continued crevassing and increased sedimentation at the location of the proto-drumlins. The drumlin relief and elongation ratio increases as the glacier erodes the sides and drapes a new till over the landform through successive surges. Our observations of this only known active drumlin field may have implications for the formation and morphological evolution of Pleistocene drumlin fields with similar composition, and our model may be tested on modern drumlins that may become exposed upon future ice retreat.

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