Glacial Features (Line) - Quad 184 (KINGSTON, NH)
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the glacial features line layer describes linear features associated with surficial geology these glacial features include but are not limited to wisconsinan synglacial sea extents meltwater channels meltwater spillways ice margins and eskers this layer also includes non glacial exposures such as gravel pit extents an associated dbase table glac_desc184l dbf is available with glacial feature descriptionsKeywords:
Meltwater
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This paper presents a glacial geomorphological map of over 17,000 landforms on the bed of a major palaeo-ice stream in Marguerite Bay, western Antarctic Peninsula. The map was compiled using various geophysical datasets from multiple marine research cruises. Eight glacial landform types are identified: mega-scale glacial lineations, crag-and-tails, whalebacks, gouged, grooved and streamlined bedrock, grounding-zone wedges, subglacial meltwater channels, gullies and channels, and iceberg scours. The map represents one of the most complete marine ice-stream signatures available for scrutiny, and these data hold much potential for reconstructing former ice sheet dynamics, testing numerical ice sheet models, and understanding the formation of subglacial bedforms beneath ice streams. In particular, they record a complex bedform signature of palaeo-ice stream flow and retreat since the last glacial maximum, characterised by considerable spatial variability and strongly influenced by the underlying geology. The map is presented at a scale of 1: 750,000, designed to be printed at A2 size, and encompasses an area of 128,420 km2.
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Deglaciation
Meltwater
Bedrock
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Pluridisciplinary fieldwork highlights features generated by an extended ice-sheet in the Djado Basin during the Hirnantian. Two glacial palaeovalley systems associated with glacial pavements and separated by thin glaciomarine interstadial series are revealed. Rigid glacial pavements characterised by abrasion erosion are differentiated from soft glacial pavements characterised by soft-bed deformation. Glacial pavements are associated with subglacial bedforms such as megaflutes, flutes and meltwater channels. They are also associated with clastic dykes and glaciotectonic structures such as deformed flutes, subglacial folds and duplex structures. This record demonstrates that ice was warm-based and flowed rapidly on the highfluid- pressure soft substrate, as for ice streams. The erosional glacial landscape is typical of areal scouring, and the depositional sediment-landform assemblage corresponds to subglacial processes. These data afford a reconstruction of glacial events which is consistent with the two polyphased low-frequency glacial cycles inferred in previous studies. During interstadial and postglacial stages, grabens, normal faults, radial extensional microfaults and extensional dihedrons were generated by extensional tectonics during glacio-isostatic rebound. In sectors highly affected by this tectonics, doleritic dykes reflect a basal crust fusion increase induced by adiabatic decompression.
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Post-glacial rebound
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Abstract Please click here to download the map associated with this article. Victoria Island lies at the north-western extremity of the region covered by the vast North American Laurentide Ice Sheet (LIS) in the Canadian Arctic Archipelago. This area is significant because it linked the interior of the LIS to the Arctic Ocean, probably via a number of ice streams. Victoria Island, however, exhibits a remarkably complex glacial landscape, with several successive generations of ice flow indicators superimposed on top of each other and often at abrupt (90°) angles. This complexity represents a major challenge to those attempting to produce a detailed reconstruction of the glacial history of the region. This paper presents a map of the glacial geomorphology of Victoria Island. The map is based on analysis of Landsat Enhanced Thematic Plus (ETM+) satellite imagery and contains over 58,000 individual glacial features which include: glacial lineations, moraines (terminal, lateral, subglacial shear margin), hummocky moraine, ribbed moraine, eskers, glaciofluvial deposits, large meltwater channels, and raised shorelines. The glacial features reveal marked changes in ice flow direction and vigour over time. Moreover, the glacial geomorphology indicates a non-steady withdrawal of ice during deglaciation, with rapidly flowing ice streams focussed into the inter-island troughs and several successively younger flow patterns superimposed on older ones. It is hoped that detailed analysis of this map will lead to an improved reconstruction of the glacial history of this area which will provide other important insights, for example, with respect to the interactions between ice streaming, deglaciation and Arctic Ocean meltwater events.
Deglaciation
Meltwater
Glacial landform
Drumlin
Terminal moraine
Wisconsin glaciation
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Deglaciation
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Meltwater drainage beneath glaciers and ice sheets is intimately linked to their dynamics. Meltwater may increase ice velocity if it acts to lubricate the bed; conversely, an efficient subglacial meltwater drainage system may preclude meltwater induced ice acceleration by limiting the amount of water available to facilitate sliding. Thus, understanding the nature of meltwater flow beneath ice masses is crucial for predicting how ice sheets and glaciers will react to increased meltwater input. However, direct observation of subglacial meltwater drainage systems is extremely difficult, meaning that indirect methods such as remote sensing, numerical modelling, dye tracing and geophysical survey are the only way to observe this environment. These methods often suffer from excessive uncertainty and poor spatial and, particularly, temporal resolution.
This thesis presents the results of an alternative approach, using the geomorphological record of eskers to understand the former behaviour of meltwater beneath the Laurentide Ice Sheet (LIS) in Canada, and at Breiðamerkurjӧkull in Iceland. Eskers are elongate, sinuous ridges of glaciofluvial sand and gravel deposited in glacial drainage channels. Despite a large body of research on eskers, no systematic analysis of the large-scale properties of eskers, or the implications this may have for understanding subglacial meltwater, has yet been undertaken. Eskers are mapped at the ice sheet (continental) scale in Canada from 678 Landsat ETM+ images and at high resolution (~30 cm) from 407 aerial photographs of the Breiðamerkurjӧkull foreland, in order to address three outstanding questions: (i) What controls the pattern and morphology of eskers? (ii) How did subglacial drainage systems evolve during ice sheet deglaciation? (iii) How can eskers be used to further our understanding of subglacial hydrology?
Over 20,000 eskers are mapped in Canada, revealing that esker systems are up to 760 km long, and are surprisingly straight. The spacing between eskers is relatively uniform and they exhibit little change in elevation from one end to another. As the LIS deglaciated between 13 cal ka and 7 cal ka, eskers increased in frequency, which is interpreted to represent an increase in meltwater drainage in channelized, rather than distributed, systems. Eskers are abundant over the resistant rocks of the Canadian Shield and also show a strong preference for formation in areas covered with till. Esker length, sinuosity and spacing appear to be unrelated to the underlying geology. Finally, two types of complex esker systems are proposed: esker fan complexes and topographically constrained esker complexes. The formation of esker complexes is dependent on sediment and meltwater supply and the pre-existing topography controls the overall shape of the esker systems.
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the glacial features line layer describes linear features associated with surficial geology these glacial features include but are not limited to wisconsinan synglacial sea extents meltwater channels meltwater spillways ice margins and eskers this layer also includes non glacial exposures such as gravel pit extents an associated dbase table glac_desc166l dbf is available with glacial feature descriptions
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During the late Wisconsinan, Southern Alaska was covered by two large ice masses; the western arm of the Cordilleran Ice Sheet and the Ahklun Mountains Ice Cap. Compared to the other ice sheets that existed during this period (e.g. the British-Irish, Laurentide and Fennoscandian ice sheets), little is known about the geomorphology they left behind. This limits our understanding of their flow pattern and retreat. Here we present systematic mapping of the glacial geomorphology of the two ice masses which existed in Southern Alaska. Due to spatially variable data availability, mapping was conducted using digital elevation models and satellite images of varying resolutions. Offshore, we map the glacial geomorphology using available bathymetric data. For the first time, we document >5000 subglacial lineations, recording ice flow direction. The distribution of moraines is presented, as well as features related to glacial meltwater drainage patterns (eskers and meltwater channels). Prominent troughs were also mapped on Alaska's continental shelf. This map provides the data required for a glacial inversion of these palaeo-ice masses.
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Lineation
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Glacial landform
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Glacial landform
Deglaciation
Drumlin
Glacial lake
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