scholarly journals Ice-sheet scale distribution and morphometry of triangular-shaped hummocks (murtoos): a subglacial landform produced during rapid retreat of the Scandinavian Ice Sheet

2019 ◽  
Vol 60 (80) ◽  
pp. 115-126 ◽  
Author(s):  
Antti E. K. Ojala ◽  
Gustaf Peterson ◽  
Joni Mäkinen ◽  
Mark D. Johnson ◽  
Kari Kajuutti ◽  
...  
Keyword(s):  
Hydraulic System ◽  
Flow Direction ◽  
Ice Sheet ◽  
Younger Dryas ◽  
Light Detection And Ranging ◽  
Ice Flow ◽  
Digital Elevation ◽  
Scandinavian Ice Sheet ◽  
Glacial Landform ◽  
Oriented Parallel

AbstractHigh-resolution digital elevation models of Finland and Sweden based on LiDAR (Light Detection and Ranging) reveal subglacial landforms in great detail. We describe the ice-sheet scale distribution and morphometric characteristics of a glacial landform that is distinctive in morphology and occurs commonly in the central parts of the former Scandinavian Ice Sheet, especially up-ice of the Younger Dryas end moraine zone. We refer to these triangular or V-shaped landforms as murtoos (singular, ‘murtoo’). Murtoos are typically 30–200 m in length and 30–200 m in width with a relief of commonly <5 m. Murtoos have straight and steep edges, a triangular tip oriented parallel to ice-flow direction, and an asymmetric longitudinal profile with a shorter, but steeper down-ice slope. The spatial distribution of murtoos and their geomorphic relation to other landforms indicate that they formed subglacially during times of climate warming and rapid retreat of the Scandinavian Ice Sheet when large amounts of meltwater were delivered to the bed. Murtoos are formed under warm-based ice and may be associated with a non-channelized subglacial hydraulic system that evacuated large discharges of subglacial water.

Coalescence of late Wisconsinan Cordilleran and Laurentide ice sheets east of the Rocky Mountain Foothills in the Dawson Creek region, northeast British Columbia, Canada

2016 ◽  
Vol 85 (3) ◽  
pp. 409-429 ◽  
Author(s):  
Adrian Scott Hickin ◽  
Olav B. Lian ◽  
Victor M. Levson
Keyword(s):  
British Columbia ◽  
Flow Direction ◽  
Ice Sheet ◽  
Rocky Mountain ◽  
Ice Flow ◽  
Oxygen Isotope Stage ◽  
Digital Elevation ◽  
Late Wisconsinan ◽  
Cordilleran Ice Sheet ◽  
River Valleys

Geomorphic, stratigraphic and geochronological evidence from northeast British Columbia (Canada) indicates that, during the late Wisconsinan (approximately equivalent to marine oxygen isotope stage [MIS] 2), a major lobe of western-sourced ice coalesced with the northeastern-sourced Laurentide Ice Sheet (LIS). High-resolution digital elevation models reveal a continuous 75 km-long field of streamlined landforms that indicate the ice flow direction of a major northeast-flowing lobe of the Cordilleran Ice Sheet (CIS) or a montane glacier (>200 km wide) was deflected to a north-northwest trajectory as it coalesced with the retreating LIS. The streamlined landforms are composed of till containing clasts of eastern provenance that imply that the LIS reached its maximum extent before the western-sourced ice flow crossed the area. Since the LIS only reached this region in the late Wisconsinan, the CIS/montane ice responsible for the streamlined landforms must have occupied the area after the LIS withdrew. Stratigraphy from the Murray and Pine river valleys supports a late Wisconsinan age for the surface landforms and records two glacial events separated by a non-glacial interval that was dated to be of middle Wisconsinan (MIS 3) age.

scholarly journals Thermomechanical modelling of the Scandinavian ice sheet: implications for ice-stream formation

1999 ◽  
Vol 28 ◽  
pp. 83-89 ◽  
Author(s):  
A. J. Payne ◽  
D.J. Baldwin
Keyword(s):  
Three Dimensional ◽  
Ice Sheet ◽  
Ice Streams ◽  
Ice Flow ◽  
Low Viscosity ◽  
Ice Stream ◽  
Scandinavian Ice Sheet ◽  
The Baltic ◽  
Stream Formation ◽  
Initial Results

AbstractThis work attempts to explain the fan-like landform assemblages observed in satellite images of the area covered by the former Scandinavian ice sheet (SIS). These assemblages have been interpreted as evidence of large ice streams within the SIS. If this interpretation is correct, then it calls into doubt current theories on the formation of ice streams. These theories regard soft sediment and topographic troughs as being the key determinants of ice-stream location. Neither can be used to explain the existence of ice streams on the flat, hard-rock area of the Baltic Shield. Initial results from a three-dimensional, thermomechanical ice-sheet model indicate that interactions between ice flow, form and temperature can create patterns similar to those mentioned above. The model uses a realistic, 20 km resolution gridded topography and a simple parameterization of accumulation and ablation. It produces patterns of maximum ice-sheet extent, which are similar to those reconstructed from the area’s glacial geomorphology. Flow in the maximum, equilibrium ice sheet is dominated by wedges of warm, low-viscosity, fast-flowing ice. These are separated by areas of cold, slow-flowing ice. This patterning appears to develop spontaneously as the modelled ice sheet grows.

scholarly journals Objective Reconstructions of the Late Wisconsinan Laurentide Ice Sheet and the Significance of Deformable Beds

2007 ◽  
Vol 39 (3) ◽  
pp. 229-238 ◽  
Author(s):  
D. A. Fisher ◽  
N. Reeh ◽  
K. Langley
Keyword(s):  
Yield Stress ◽  
Flow Direction ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Hudson Bay ◽  
Ice Streams ◽  
Ice Flow ◽  
Surface Slopes ◽  
Late Wisconsinan

ABSTRACT A three dimensional steady state plastic ice model; the present surface topography (on a 50 km grid); a recent concensus of the Late Wisconsinan maximum margin (PREST, 1984); and a simple map of ice yield stress are used to model the Laurentide Ice Sheet. A multi-domed, asymmetric reconstruction is computed without prior assumptions about flow lines. The effects of possible deforming beds are modelled by using the very low yield stress values suggested by MATHEWS (1974). Because of low yield stress (deforming beds) the model generates thin ice on the Prairies, Great Lakes area and, in one case, over Hudson Bay. Introduction of low yield stress (deformabie) regions also produces low surface slopes and abrupt ice flow direction changes. In certain circumstances large ice streams are generated along the boundaries between normal yield stress (non-deformable beds) and low yield stress ice (deformabie beds). Computer models are discussed in reference to the geologically-based reconstructions of SHILTS (1980) and DYKE ef al. (1982).

scholarly journals Precise altimetric topography in ice-sheet flow studies

1993 ◽  
Vol 17 ◽  
pp. 195-200 ◽  
Author(s):  
F. Remy ◽  
J.F. Minster
Keyword(s):  
Activation Energy ◽  
Flow Direction ◽  
Ice Sheet ◽  
Rheological Parameters ◽  
Least Squares Regression ◽  
Sheet Flow ◽  
Ice Flow ◽  
Flow Models ◽  
Altimetric Data ◽  
Basal Shear

The precision of radar altimetry above an ice sheet can improve glaciological studies such as mass balance surveys or ice-sheet flow models, the first by comparing altimetric data at different times (see this issue), the second by testing or constraining models with data. This paper is a first step towards the latter. From a precise topography deduced by inversion of altimetric data (Remy and others, 1989), we calculate ice-flow direction, balance velocity and basal shear stress. The rheological parameters involved in the relation linking velocity, stress and temperature are then derived by least-squares regression. Ice flow is well represented by setting the Glen parameter,nto 1 ± 0.25 and the activation energy as 70 ± 10 kJ mol−1.

scholarly journals Towards a GIS assessment of numerical ice-sheet model performance using geomorphological data

2007 ◽  
Vol 53 (180) ◽  
pp. 71-83 ◽  
Author(s):  
Jacob Napieralski ◽  
Alun Hubbard ◽  
Yingkui Li ◽  
Jon Harbor ◽  
Arjen P. Stroeven ◽  
...  
Keyword(s):  
Flow Direction ◽  
Ice Sheet ◽  
Model Performance ◽  
Initial Step ◽  
Ice Flow ◽  
Flow Models ◽  
Flow Directions ◽  
The Last Glacial Maximum ◽  
Basal Flow ◽  
The Last Glacial

AbstractA major difficulty in assimilating geomorphological information with ice-sheet models is the lack of a consistent methodology to systematically compare model output and field data. As an initial step in establishing a quantitative comparison methodology, automated proximity and conformity analysis (APCA) and automated flow direction analysis (AFDA) have been developed to assess the level of correspondence between modelled ice extent and ice-marginal features such as end moraines, as well as between modelled basal flow directions and palaeo-flow direction indicators, such as glacial lineations. To illustrate the potential of such an approach, an ensemble suite of 40 numerical simulations of the Fennoscandian ice sheet were compared to end moraines of the Last Glacial Maximum and the Younger Dryas and to glacial lineations in northern Sweden using APCA and AFDA. Model experiments evaluated in this manner were ranked according to level of correspondence. Such an approach holds considerable promise for optimizing the parameter space and coherence of ice-flow models by automated, quantitative assessment of multiple ensemble experiments against a database of geological or glaciological evidence.

scholarly journals Ice-sheet flow features and rheological parameters derived from precise altimetric topography

1996 ◽  
Vol 23 ◽  
pp. 277-283 ◽  
Author(s):  
F. Rémy ◽  
C. Ritz ◽  
L. Brisset
Keyword(s):  
Shear Stress ◽  
Flow Direction ◽  
Ice Sheet ◽  
Rheological Parameters ◽  
Topographic Map ◽  
Radar Altimeter ◽  
Sheet Flow ◽  
Ice Flow ◽  
Exponential Factor ◽  
Flow Features

For the first time high-quality coverage of the ERS-1 radar altimeter provides a very accurate surface topographic map covering 80% of the Antarctic ice sheet that can contribute significantly to glaciological studies such as ice-sheet flow modelling. The topography allows estimation of the ice-flow direction, the balance velocity and the basal shear stress. A relationship between shear stress, basal temperature and a parameter related to strain rate helps in mapping the behaviour anomalies of these parameters. Longitudinal stress, sliding, bedrock topography and variation in the pre-exponential factor of the flow law are found to play a major role in the ice-flow pattern. This relation can also be used to estimate rheological parameters: the Glen exponent n is found to be 1 for T < −10°C and 3–4 for higher temperatures, where Q is found to be 70 kJ mol−1.

scholarly journals GIS dataset: geomorphological record of terrestrial-terminating ice streams, southern sector of Baltic Ice Stream Complex, last Scandinavian Ice Sheet, Poland

2021 ◽  
Author(s):  
Izabela Szuman ◽  
Jakub Z. Kalita ◽  
Marek W. Ewertowski ◽  
Chris D. Clark ◽  
Stephen J. Livingstone ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Ice Streams ◽  
Southern Sector ◽  
Ice Stream ◽  
Digital Elevation ◽  
Scandinavian Ice Sheet ◽  
Data Source ◽  
Elevation Model ◽  
The Baltic ◽  
The Last Glacial

Abstract. Here we present a comprehensive dataset of glacial geomorphological features covering an area of 65 000 km2 in central west Poland, located along the southern sector of the last Scandinavian Ice Sheet, within the limits of the Baltic Ice Stream Complex. The GIS dataset is based on mapping from a 0.4 m high-resolution Digital Elevation Model derived from airborne Light Detection and Ranging data. Ten landform types have been mapped: Mega-Scale Glacial Lineations, drumlins, marginal features (moraine chains, abrupt margins, edges of ice-contact fans), ribbed moraines, tunnel valleys, eskers, geometrical ridge networks and hill-hole pairs. The map comprises 5461 individual landforms or landform parts, which are available as vector layers in GeoPackage format at http://doi.org/10.5281/zenodo.4570570 (Szuman et al., 2021a). These features constitute a valuable data source for reconstructing and modelling the last Scandinavian Ice Sheet extent and dynamics from the Middle Weichselian Scandinavian Ice Sheet advance, 50–30 ka BP, through the Last Glacial Maximum, 25–21 ka BP and Young Baltic Advances, 18–15 ka BP. The presented data are particularly useful for modellers, geomorphologists and glaciologists.

Tephrochronological evidence of a later Younger Dryas ice-sheet maximum in central Norway

2021 ◽  
Author(s):  
Simon A. Larsson ◽  
Stefan Wastegård ◽  
Fredrik Høgaas
Keyword(s):  
Radiocarbon Dating ◽  
Ice Sheet ◽  
Younger Dryas ◽  
Coastal Lake ◽  
Cold Event ◽  
Western Norway ◽  
Scandinavian Ice Sheet ◽  
Marine Fossils ◽  
Ice Sheet Dynamics ◽  
Southern Norway

&lt;p&gt;The Scandinavian Ice Sheet responded time-transgressively to the Younger Dryas (Greenland Stadial 1) cold event with large regional variations. Around Trondheimsfjorden in central Norway, the Tautra Moraines and the Hoklingen Moraines have long been assumed to have formed by glacial readvances during this event, as they have been dated to c. 12.7 and 11.6 cal. ka BP respectively (Olsen et al., 2015), mainly based on radiocarbon dating of often marine fossils. The Tautra Moraines, being the outer ridges of the two, should thus represent the maximum ice-sheet extent in this region during the Younger Dryas.&lt;/p&gt;&lt;p&gt;This ice-front position established a pro-glacial lake west of present-day Leksvik village on the Fosen peninsula (Selnes, 1982), which covered the Lomtj&amp;#248;nnin lakes and Lomtj&amp;#248;nnmyran fens, and drained through a spillway via Lake R&amp;#248;rtj&amp;#248;nna. Some 20 km inland (northeast) from this location, inside the Tautra Moraines, the location of the Dam&amp;#229;smyran bog was covered by the ice sheet at that time.&lt;/p&gt;&lt;p&gt;By examining sediments from these sites for occurrences of volcanic ashes (visible and cryptotephra), combined with radiocarbon dating, we find that the ice front remained at the Tautra Moraines until the late Younger Dryas, contrary to the previous chronology (and overriding the suggested formation age of the Hoklingen Moraines). These findings comply with several recent reconstructions of the deglaciation at other sites in western (Lohne et al., 2012; Mangerud et al., 2016) and southern Norway (Romundset et al., 2019) and are a strong example of the usefulness of tephrochronology in the reconstruction of past ice-sheet dynamics.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Lohne, &amp;#216;.S., Mangerud, J. &amp; Svendsen, J.I. (2012) Timing of the Younger Dryas glacial maximum in Western Norway. &lt;em&gt;Journal of Quaternary Science&lt;/em&gt;, vol. 27, pp. 81&amp;#8211;88.&lt;/p&gt;&lt;p&gt;Mangerud, J., Aarseth, I., et al. (2016) A major re-growth of the Scandinavian Ice Sheet in western Norway during Aller&amp;#248;d&amp;#8211;Younger Dryas. &lt;em&gt;Quaternary Science Reviews&lt;/em&gt;, vol. 132, pp. 175&amp;#8211;205.&lt;/p&gt;&lt;p&gt;Olsen, L., H&amp;#248;gaas, F. &amp; Sveian, H. (2015) Age of the Younger Dryas ice-marginal substages in Mid-Norway&amp;#8212;Tautra and Hoklingen, based on a compilation of 14C-dates. &lt;em&gt;Norges geologiske unders&amp;#248;kelse Bulletin&lt;/em&gt;, vol. 454, pp. 1&amp;#8211;13.&lt;/p&gt;&lt;p&gt;Romundset, A., Lakeman, T.R. &amp; H&amp;#248;gaas, F. (2019) Coastal lake records add constraints to the age and magnitude of the Younger Dryas ice-front oscillation along the Skagerrak coastline in southern Norway. &lt;em&gt;Journal of Quaternary Science&lt;/em&gt;, vol. 34, pp. 112&amp;#8211;124.&lt;/p&gt;&lt;p&gt;Selnes, H. (1982) Paleo-&amp;#248;kologiske unders&amp;#248;kelser omkring israndavsetninger p&amp;#229; Fosenhalv&amp;#248;ya, Midt-Norge. Thesis at the Department of Botany, University of Trondheim.&lt;/p&gt;

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