| 1. |
- Benediktsson, Ívar Örn, et al.
(författare)
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Progressive formation of modern drumlins at Múlajökull, Iceland: stratigraphical and morphological evidence
- 2016
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 45, s. 567-583
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Tidskriftsartikel (refereegranskat)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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| 2. |
- Ingolfsson, Olafur, et al.
(författare)
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Glacial geological studies of surge-type glaciers in Iceland — Research
- 2016
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Ingår i: Earth-Science Reviews. - : Elsevier BV. - 0012-8252. ; 152, s. 37-69
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Tidskriftsartikel (refereegranskat)abstract
- Surging glaciers are potential analogues for land-terminating palaeo-ice streams and surging ice sheet lobes, and research on surge-type glaciers is important for understanding the causal mechanisms of modern and past ice sheet instabilities. The geomorphic signatures left by the Icelandic surge-type glaciers vary and range from glaciotectonic end moraines formed by folding and thrusting, crevasse-squeeze ridges, concertina eskers, drumlins and fluted forefields, to extensive dead-ice fields and even drift sheets where fast ice-flow indicators are largely missing. We outline some outstanding research questions and review case studies from the surge-type outlets of Brúarjökull, Eyjabakkajökull and Tungnaárjökull (Vatnajökull ice cap), Múlajökull and Sátujökull (Hofsjökull ice cap), Hagafellsjökull and Suðurjökull (Langjökull ice cap), Kaldalónsjökull, Leirufjarðarjökull and Reykjarfjarðarjökull (Drangajökull ice cap), as well as the surge-type cirque glaciers in northern Iceland. We review the current understanding of how rapid ice flow is sustained throughout the surge, the processes that control the development of the surge-type glacier landsystem and the geological evidence of surges found in sediments and landforms. We also examine if it is possible to reconstruct past surge flow rates from glacial landforms and sediments and scale-up present-day surge processes, landforms and landsystems as modern analogues to past ice streams. Finally,we also examine if there is a climate/mass-balance control on surge initiation, duration and frequency.
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| 3. |
- Jónsson, Sverrir Aðalsteinn, et al.
(författare)
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The drumlin field and the geomorphology of the Múlajökull surge-type glacier, central Iceland
- 2014
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Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 207, s. 213-220
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Tidskriftsartikel (refereegranskat)abstract
- Here we present a new geomorphological map of the active drumlin field and the forefield of Múlajökull, a surge-type outlet glacier, Iceland. The map is based on aerial photographs taken in 1995 and LiDAR data recorded in 2008. Mapping was done using ArcGIS 10 software on orthorectified imagery, LiDAR data and digital elevation models. The mapped landforms were initially identified on the aerial imagery and LiDAR and then ground-checked in the field. We mapped subglacial, supraglacial, ice-marginal, periglacial, and glaciofluvial landforms. The geomorphology of the Múlajökull forefield is similar to that of the forefields of other surge-type glaciers in Iceland: with a highly streamlined forefield, crevasse-fill ridges, and series of glaciotectonic end moraines. However, the large number (i.e., 110) of drumlins forming the drumlin field is unique for modern Icelandic surge-type glaciers and, as yet, unique for contemporary glaciers in general. Also apparent is that the drumlins are wider and shorter in the distal part of the drumlin field and narrower and longer in the proximal part. Hence, the mapping reveals a development of the drumlins toward a more streamlined shape of the proximal landforms that have experienced more surges. The drumlins in the drumlin field are active, i.e., they form during the modern surges of Múlajökull.
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| 4. |
- Jonsson, Sverrir, et al.
(författare)
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THE MÚLAJÖKULL DRUMLIN FIELD - SEDIMENTOLOGY AND GEOMORPHOLOGY
- 2011
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Ingår i: Geological Society of America abstracts with programs Minneapolis 2011.
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Konferensbidrag (refereegranskat)abstract
- The drumlin field in front of Múlajökull, a surge-style, outlet glacier from Hofsjökull in Iceland, is the only known active drumlin field (Johnson et al., 2010). The aim of this study is to further explore the formation of drumlins in a modern glacial environment. We use data from geological sections, DEMs, aerial imagery and field mapping. Here we present preliminary results from section logging and geomorphological mapping in the summer of 2011. Geomorphological mapping of the drumlin field both with DEMs and ground proofing has revealed over 100 drumlins and a number of drumlinized ridges. The drumlins furthest from the present ice margin appear broader and have lower relief than those closer to the ice. We suggest that this reflects an evolution of the drumlin form during recurrent surging. The drumlins farther away from the ice have experienced fewer surges than those that have just been uncovered due to retreat of the ice margin. During successive surges, the drumlins become narrower and develop higher relief. In one section close to the present ice margin, we identified at least 9 till beds in the crest of a drumlin, each likely the product of a surge, representing approximately 1/3 of the drumlin relief. The top till bed parallels the drumlin form and truncates the older tills. The older units also dip parallel to the drumlin form, but at a slightly lower angle. We believe that this represents an earlier, broader shape of the drumlin prior to the more recent surges, implying an evolution of form similar to that seen in the evolution in form in the drumlin field. The Múlajökull drumlins have thus grown during surging by erosion on the proximal end and sides of the drumlin followed by accretion of till sheets concentrically on the resulting form.
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| 5. |
- Schomacker, Anders, et al.
(författare)
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THE ACTIVE DRUMLIN FIELD AT THE MÚLAJÖKULL SURGE-TYPE GLACIER, ICELAND – GEOMORPHOLOGY AND SEDIMENTOLOGY
- 2011
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Ingår i: Geological Society of America abstracts with programs Minnespolis 2011.
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Konferensbidrag (refereegranskat)abstract
- Recent marginal retreat of Múlajökull, a surge-type, outlet glacier of the Hofsjökull ice cap, central Iceland, has revealed a drumlin field consisting of over 50 drumlins. The drumlins are 90–320 m long, 30–105 m wide, 5–10 m in relief, and composed of multiple beds of till deposited by lodgement and bed deformation. The youngest till layer truncates the older units with an erosion surface that parallels the drumlin form. Thus, the drumlins are built up and formed by a combination of subglacial depositional and erosional processes. Field evidence suggests each till bed to be associated with individual, recent surges. We consider the drumlin field to be active in the sense that the drumlins are shaped by the current glacial regime. To our knowledge, the Múlajökull field is the only known active drumlin field and is, therefore, a unique analogue to Pleistocene drumlin fields.
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