Abstract
A surficial geology and geomorphology map of the forelands of the Sandfellsjökull and Oldufellsjökull piedmont lobes of the east Mýrdalsjökull ice cap is used to characterise the historical and modern landscape imprint in a glacial landsystems context. This serves as a modern analogue for palaeoglaciological reconstructions of ice cap systems that operated outlet lobes of contrasting dynamics, but the subtle variability in process-form regimes is encoded in the geomorphology. The landsystems of the two piedmont lobes reflect significantly different process-form regimes, and hence contrasting historical glacier dynamics, despite the fact that they are nourished by the same ice cap. The Sandfellsjökull landsystem displays the diagnostic criteria for active temperate glacier operation, including arcuate assemblages of inset minor push moraines and associated flutings, kame terrace and ice-dammed lake deposits, linear sandar directed by overridden moraine arcs, and since 1945, features, such as ice-cored, pitted, and glacially pushed outwash fans that are linked to englacial esker networks representative of recession into an overdeepening. Moraine plan forms have also changed from weakly crenulated and discontinuous curvilinear ridges to sawtooth features and crevasse-squeeze ridges and till eskers in response to changing proglacial drainage conditions. The Oldufellsjökull landsystem displays subtle signatures of jökulhlaup-driven surges, including sparse and widely spaced moraine clusters that are separated by exceptionally long flutings. The subtlety of the surge imprint at Oldufellsjökull was recognised only by comparison with nearby Sandfellsjökull, suggesting that palaeo-surging has likely been under-estimated in the ancient landform record. Hence, the simple imprint of sparse and widely spaced moraine clusters that are separated by exceptionally long flutings should be included as possible surge-diagnostic criteria.
Highlights
Mapping sediment-landform associations on modern glacier forelands facilitates a better understanding of the nature of spatial and temporal change in glacial process-form regimes
The surficial geology and geomorphology map (Figure 6) reveals that the glacier forelands are characterized by only four sediment-landform units, including: till and moraines that were deposited during and since the historical Little Ice Age (LIA) Type Period; glacifluvial deposits; push moraines developed in ice-contact glacifluvial deposits; and, glacilacustrine deposits modified by glacifluvial processes
The arcuate assemblages of inset minor push moraines and associated flutings on the Sandfellsjökull foreland, in addition to kame terrace and ice-dammed lake deposits and linear sandar directed by overridden moraine arcs, are all diagnostic of the active temperate landsystem, as documented elsewhere in southern Iceland [3,6,9,12,55,56,57,76,77] and more locally at the colder end of the active temperate spectrum at the northeastern margins of Mýrdalsjökull [1,48,49,50]
Summary
Mapping sediment-landform associations on modern glacier forelands facilitates a better understanding of the nature of spatial and temporal change in glacial process-form regimes. A variety of glacierization styles has been collated from the historically deglaciated forelands of Iceland [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20], important subtleties in the imprints of glacial process-form regimes still remain to be elucidated. Evans etetal., landsystems of Sandfellsjökull and Oldufellsjökull, as presented by the the new new mapping mapping reported reported here, here, constitute important modern analogues for employment in palaeoglaciological reconstructions of ice cap systems operated outlet lobes lobes of contrasting dynamics.
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