| 1. |
- Benediktsson, Ivar Örn, et al.
(författare)
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Architecture and structural evolution of an early Little Ice Age terminal moraine at the surge-type glacier Mulajokull, Iceland
- 2015
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Ingår i: Journal of Geophysical Research - Earth Surface. - 2169-9011 .- 0148-0227 .- 2156-2202. ; 120:9, s. 1895-1910
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Tidskriftsartikel (refereegranskat)abstract
- 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 Radiocarbon dating and analysis of tephra layers, along with historical references, indicate that the most likely time of moraine formation was between A.D. 1717 and 1760, which suggests that Mulajokull had its Little Ice Age maximum and most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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| 2. |
- Benediktsson, Ivar Örn
(författare)
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Polyphase structural evolution of a fine-grained, fold-dominated end moraine, Bruarjokull surge-type glacier, Iceland
- 2012
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Ingår i: Jökull: Journal of the Glaciological and Geological Societies of Iceland. - 0449-0576. ; 62, s. 167-184
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Tidskriftsartikel (refereegranskat)abstract
- The glaciotectonic architecture and structural evolution of a fine-grained end moraine formed by the 1890 glacier surge of Bruarjokull is described from four excavated cross-sections. The end moraine ridge is a morphological expression of a marginal sedimentary wedge formed during the last days of the surge. The actual end-moraine ridge was formed on the last day of the 1890 surge when the glacier became coupled to the bed and ploughed into the reverse slope of the marginal sediment wedge. Ductile deformation, favoured by high porewater pressure, dominated the construction of the end moraine while brittle deformation was induced when porewater pressure decreased, particularly at the end of the surge. Thus, the deformation was polyphase, developing from open folding to multiple overfolding when porewater pressure was high and finally to overthrusting, faulting and shearing at the very end of the surge when porewater pressure dropped severely upon porewater blow-out in front of the moraine. This structural continuum is exhibited by the four cross-sections. The glaciotectonic stress was absorbed within a relatively narrow zone due to high friction along a basal decollement. A new model illustrates the structural evolution of a fine-grained, fold-dominated end moraine and may serve as an analogue to similar end moraines in modern and Pleistocene environments.
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| 3. |
- 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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| 4. |
- Chandler, Benjamin M. P., et al.
(författare)
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Glacial geomorphological mapping : A review of approaches and frameworks for best practice
- 2018
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Ingår i: Earth-Science Reviews. - : Elsevier BV. - 0012-8252 .- 1872-6828. ; 185, s. 806-846
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Forskningsöversikt (refereegranskat)abstract
- Geomorphological mapping is a well-established method for examining earth surface processes and landscape evolution in a range of environmental contexts. In glacial research, it provides crucial data for a wide range of process-oriented studies and palaeoglaciological reconstructions; in the latter case providing an essential geomorphological framework for establishing glacial chronologies. In recent decades, there have been significant developments in remote sensing and Geographical Information Systems (GIS), with a plethora of high quality remotely-sensed datasets now (often freely) available. Most recently, the emergence of unmanned aerial vehicle (UAV) technology has allowed sub-decimetre scale aerial images and Digital Elevation Models (DEMs) to be obtained. Traditional field mapping methods still have an important role in glacial geomorphology, particularly in cirque glacier, valley glacier and icefield/ice-cap outlet settings. Field mapping is also used in ice sheet settings, but often takes the form of necessarily highly-selective ground-truthing of remote mapping. Given the increasing abundance of datasets and methods available for mapping, effective approaches are necessary to enable assimilation of data and ensure robustness. This paper provides a review and assessment of the various glacial geomorphological methods and datasets currently available, with a focus on their applicability in particular glacial settings. We distinguish two overarching 'work streams' that recognise the different approaches typically used in mapping landforms produced by ice masses of different sizes: (i) mapping of ice sheet geomorphological imprints using a combined remote sensing approach, with some field checking (where feasible); and (ii) mapping of alpine and plateau-style ice mass (cirque glacier, valley glacier, icefield and ice-cap) geomorphological imprints using remote sensing and considerable field mapping. Key challenges to accurate and robust geomorphological mapping are highlighted, often necessitating compromises and pragmatic solutions. The importance of combining multiple datasets and/or mapping approaches is emphasised, akin to multi-proxy approaches used in many Earth Science disciplines. Based on our review, we provide idealised frameworks and general recommendations to ensure best practice in future studies and aid in accuracy assessment, comparison, and integration of geomorphological data. These will be of particular value where geomorphological data are incorporated in large compilations and subsequently used for palaeoglaciological reconstructions. Finally, we stress that robust interpretations of glacial landforms and landscapes invariably requires additional chronological and/or sedimentological evidence, and that such data should ideally be collected as part of a holistic assessment of the overall glacier system.
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| 5. |
- Flindt, Anne-Cecille, et al.
(författare)
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A pre-LGM sandur at Fiskarheden in NW Dalarna, Sweden – sedimentology and glaciotectonic deformation.
- 2018
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Ingår i: Boreas. - : Wiley. - 1502-3885 .- 0300-9483. ; 47:3, s. 711-737
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Tidskriftsartikel (refereegranskat)abstract
- The Fiskarheden quarry, situated in NW Dalarna, central Sweden, reveals thick coarse-grained sediments of Scott type facies association representing a sandur deposited in an ice-proximal proglacial environment. Optically Stimulated Luminescence (OSL) dating of the sandur sediments suggests a pre-Last Glacial Maximum (LGM) age. Most acquired ages are pre-Saalian (>200 ka) and we regard each of these ages to represent non/poorly bleached sediment except for one small-aliquot OSL age of 98±6 ka. This age comes from the top surface of an arguably well-bleached sand bed deposited on the lee-side of a braid-bar, putting the sandur build-up into the Early Weichselian. Large-scale glaciotectonic structures show an imbricate thrust fan involving both ductile and brittle deformation. The deformation was from the WNW, which largely coincides with the formative trend of the predominating streamlined terrain and Rogen moraine tracts surrounding Fiskarheden. It is suggested that the deformation of the sandur sediments took place when the advancing glacier approached and pushed its own proglacial outwash sediment, during an ice-marginal oscillation either at the inception of one of the Early Weichselian glaciations in the area, or during a general ice retreat amid a deglacial phase. The Fiskarheden sandur deposits are covered by a subglacial traction till deposited from the NE/NNE. This direction corresponds with younger streamlined terrain flowsets cross-cutting the older NNW–SSE system and probably represents deglaciation in the area following the LGM. This study will add to the understanding of the formation and deformation of Pleistocene sandur successions and their relationship to past ice-sheet behaviour.
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| 6. |
- 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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| 7. |
- Johansson, Jonas, et al.
(författare)
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Assessing applicants for PhD-positions: How to pick the right one?
- 2014
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Ingår i: 8:e Pedagogiska Inspirationskonferensen 2014. - 2003-3761 .- 2003-377X. ; 8
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Konferensbidrag (refereegranskat)abstract
- This study focuses on the assessment and selection of applicants for doctoral positions. The empirical data was gathered through a survey among faculty staff at Lund University, Sweden. The findings are also contrasted against the literature within the subject area, which is surprisingly scarce. One interesting finding of the survey is the frequent use of interviews and infrequent use of other assessment methods, such as personality tests or tasks, to assess applicants. Further, interviews are believed by the respondents to have a high predictive value on the applicants’ performance in a doctoral program, despite doubts in the literature. These results seem to be in contrast with the experience and common practice outside academia. This might be attributed to the fact that all doctoral recruitments are carried out by supervisors and co-supervisors, who are usually not professionally trained in assessing and selecting applicants -
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| 8. |
- Johnson, Mark D., 1954, et al.
(författare)
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SUBMARINE PUSH MORAINES OF THE MIDDLE SWEDISH END MORAINE ZONE
- 2011
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Ingår i: Geological Society of America abstracts with programs Minneapolis 2011.
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Konferensbidrag (refereegranskat)abstract
- During the Younger Dryas cold event (YD), the Scandinavian Ice Sheet formed the Middle Swedish end-moraine zone (MSEMZ) in south-central Sweden. The area around Skara was below sea level during the YD, and thick marine, varved clay was deposited proglacially on scoured bedrock in the ocean prior to, during, and after the YD. Recent highway exposures in four of the seven ridges in the MSEMZ reveal that, during overall retreat, the ice margin oscillated and, during each oscillation, deformed the marine clay into moraine ridges. The push moraines have little to no till, and then only on the proximal sides. A range of deformation structures are present including folded-and-thrusted to remobilized varved clay. At Ledsjö, a double oscillation is apparent with a grounding-line fan of sand formed between the two oscillations, which was then deformed. The grounding-line-fan sands are faulted and boudinized within 100 m of the former ice margin. Sand in boudins in places retains primary sedimentary structures, but elsewhere show fluidized flow. Farther up-ice, the clay and sands are complexly sheared along down-glacier-dipping reverse faults of several scales (cm to 10´s of m) indicating a subglacial tensional environment. At Ledsjö and Gullhammar, an upper, structureless clay likely represents proglacial, submarine, mudflow sediment deposited on the distal slope of the moraine. These exposures provide models for recent submarine push moraines imaged in fjords in Norway and Svalbard.
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| 9. |
- Johnson, Mark D., 1954, et al.
(författare)
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The Ledsjo end moraine-a subaquatic push moraine composed of glaciomarine clay in central Sweden
- 2013
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Ingår i: Proceedings of the Geologists' Association. - : Elsevier BV. - 0016-7878. ; 124:5, s. 738-752
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Tidskriftsartikel (refereegranskat)abstract
- During the Younger Dryas cold event, the Scandinavian ice sheet readvanced in southwest Sweden and formed the Middle Swedish end-moraine zone (MSEMZ). Recent highway construction near Skara has created an exposure through the prominent ridge at Ledsjo. Through sketching and measurement of structural information, we have documented the internal character of the Ledsjo moraine. The moraine consists predominantly of clay with numerous sand pods and lenses, which show undeformed, brittle deformed, or fluidized structures. Based on geomorphology and structural geology, it is clear the moraine was made during two advances. As ice advanced, proglacial marine clay was subglacially mobilized by the ice and extruded at the ice margin forming a ramp of debris-flow sediment. Contemporaneously, subglacial meltwater transported sand to the margin, where the meltwater became a buoyant plume, and sand was deposited near the ice margin by currents moving away from as well as toward the ice margin. These processes resulted in interbedded sand and clay. Continued advance of the ice margin deformed this package and further pushed the assemblage into a ridge form with gravity sliding of portions of the ridge. Prior to the second advance, sand was deposited on the proximal side of the initial ridge. During readvance, this sand was thrust faulted and intruded by mobilized clay. Up ice of the intruded sands, subglacial, extensional deformation created a complex shear zone of faulted sand and clay. The Ledsjo moraine represents a subaerial example of submarine push moraines like the submerged moraines recently documented in Svalbard. (c) 2012 The Geologists' Association. Published by Elsevier Ltd. All rights reserved.
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| 10. |
- 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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