Architecture and structural evolution of an early Little Ice Age terminal moraine at the surge-type glacier Mulajokull, Iceland

The internal architecture and structural evolution of the Arnarfellsmular terminal moraine at Mulajokull, a surge-type glacier in central Iceland, is described in order to demonstrate submarginal and proglacial glaciotectonic processes during glacier surging, as well as constraining the age of the m...

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Bibliographic Details
Published in:Journal of Geophysical Research: Earth Surface
Main Authors: Benediktsson, Ivar Örn, Schomacker, Anders, Johnson, Mark D., Geiger, Alessa J., Ingolfsson, Olafur, Guomundsdottir, Esther Ruth
Format: Article in Journal/Newspaper
Language:English
Published: American Geophysical Union (AGU) 2015
Subjects:
Geology
glaciotectonic
moraine
folding and thrusting
horizontal shortening
surge-type glacier
Mulajokull
Crest The
glacier
Iceland
Online Access:https://lup.lub.lu.se/record/8201600
https://doi.org/10.1002/2015JF003514
Description
Summary:The internal architecture and structural evolution of the Arnarfellsmular terminal moraine at Mulajokull, a surge-type glacier in central Iceland, is described in order to demonstrate submarginal and proglacial glaciotectonic processes during glacier surging, as well as constraining the age of the maximum extent of the glacier. The moraine is 4-7m high, 50-100m wide, and composed of a highly deformed sequence of loess, peat, and tephra that is draped by till up to the crest. The internal architecture is dominated by steep, high-amplitude overturned folds and thrusts in the crest zone but open, low-amplitude folds on the distal slope. Section balancing suggests a basal detachment (decollement) depth of 1.4m and a total horizontal shortening of around 59%. This implies that the glacier coupled to the foreland about 70m up glacier from its terminal position to initiate the formation of the moraine. The structural evolution is polyphase in that the formation commenced with low-amplitude open folding of the foreland, followed by overfolding and piggyback thrusting. Radiocarbon dating and analysis of tephra layers, along with historical references, indicate that the most likely time of moraine formation was between A.D. 1717 and 1760, which suggests that Mulajokull had its Little Ice Age maximum and most extensive surge earlier than many other surge-type glaciers in Iceland.

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