Distribution of Patterned Ground and Surficial Deposits on a Debris-covered Glacier Surface in Mullins Valley and Upper Beacon Valley, Antarctica
Beacon Valley is located in the western Dry Valleys, Antarctica, adjacent to the East Antarctic Ice Sheet (EAIS). The surficial material on the floor of Beacon Valley is segmented into large polygonal landforms separated by trenches. Buried beneath the polygons and surficial material is massive grou...
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DigitalCommons@UMaine
2002
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| Online Access: | https://digitalcommons.library.umaine.edu/etd/597 https://digitalcommons.library.umaine.edu/context/etd/article/1622/viewcontent/LorreyAM2002.pdf |
| Summary: | Beacon Valley is located in the western Dry Valleys, Antarctica, adjacent to the East Antarctic Ice Sheet (EAIS). The surficial material on the floor of Beacon Valley is segmented into large polygonal landforms separated by trenches. Buried beneath the polygons and surficial material is massive ground ice. One hypothesis is that the buried ice in upper Beacon Valley is glacier ice originating from local debris-covered glaciers. The networks of polygons and trenches form as the buried ice undergoes thermal contraction and sublimation. Contraction cracks that penetrate the surficial material and buried ice in Beacon Valley contain Late Miocene age volcanic ashes. The ashes postdate the buried ice. The preservation of such old ice implies a continuous extreme polar condition in Beacon Valley since late Miocene time. An alternative explanation is that the buried ice in Beacon Valley is modem ground ice that formed from percolation of melted, wind-blown snow that subsequently froze within the sediment mantle. Polygonal landforms would result from the seasonal freeze-thaw of the modem ground ice and surficial material. Continual freeze-thaw action, or cryoturbation, would create a mass of coalesced, modern ice lenses covered with older sediment. The buried ice in this case could be young, and hence could not be used to imply stable climatic conditions in Beacon Valley since the late Miocene. Polygons cover the surface of a debris-covered glacier that fills part of upper Beacon Valley and Mullins Valley. A survey of the debris-covered glacier surface indicates that polygons mature with distance from the equilibrium line. The polygon morphology highlights the transport path of the buried ice in upper Beacon Valley, which can be sourced to the cirque (accumulation zone) at the head of Mullins Valley. The buried ice in upper Beacon Valley is part of a coherent, massive ice body of glacial origin. A gray diamicton is draped over the buried ice. It has textural and weathering characteristics akin to englacial, buried ice ... |
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