page_title: Overdeepening
section_title: Geomorphology
hierarchical_section_title: Overdeepening / Geomorphology
caption_attribution_description: English: Overdeepened basins in the Gamburtsev mountains in Antarctica. The data from which this plot was made is found in {{cite doi|10.1038/nature08024 }}
context_page_description: Overdeepening is a characteristic of basins and valleys eroded by glaciers. An overdeepened valley profile is often eroded to depths which are hundreds of metres below the deepest continuous line along a valley or watercourse. This phenomenon is observed under modern day glaciers, in salt-water fjords and fresh-water lakes remaining after glaciers melt, as well as in tunnel valleys which are partially or totally filled with sediment. When the channel produced by a glacier is filled with debris, the subsurface geomorphic structure is found to be erosionally cut into bedrock and subsequently filled by sediments. These overdeepened cuts into bedrock structures can reach a depth of several hundred metres below the valley floor.
  Overdeepened fjords and lakes have significant economic value as harbours and fisheries. Overdeepened basins and valleys filled with sediment are of particular interest to engineers, petroleum geologists, and hydrologists; engineers apply the information for developing foundations and tunnel construction, petroleum geologists use tunnel valley locations to identify potential oil fields, while hydrologists apply this knowledge for groundwater resource management.
context_section_description: Glacial erosion proceeds by abrasion as ice and entrained debris moves across the underlying bedrock, by water induced erosion and transport of sediment, and by freeze-thaw cycles which weather the bedrock. All processes are most effective at the bottom of glacial ice - hence the glacier erodes at the bottom. The presence of ice in the gap reduces the rate at which the side walls weather, yielding steep side walls. When the course of glacial ice flow is constrained by surrounding topography, the narrowest regions of flow will abrade most rapidly and cut most deeply, even to depths over 1000 meters below sea level. The resulting profile, when observed through the ice with radar or when evident after the ice had melted, is referred to as overdeepened. Although research remains in fully understanding the processes involved, significant progress has been evident in the late 20th and early 21st centuries.  This section details major elements in the emerging understanding of the processes which produce overdeepening.
  Glaciologists performed a detailed radar survey of Antarctica's Gamburtsev Mountains during the International Polar Year, allowing both the overlying glacial ice thickness and the elevation of the bedrock below to be found. The survey shows overdeepening in the valley floors of up to 432 metres (1,417 ft) while the valleys exhibit steep side troughs. The figure to the left shows the three major regions of overdeepening, of 3 kilometres (2 mi), 6 kilometres (4 mi), and 16 kilometres (10 mi) in length.  Portions of this profile will be used to illustrate the formation of overdeepened valleys.
caption: Overdeepened basins in the Gamburtsev Mountains of Antarctica.
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