The hydrology of subglacial overdeepenings: A new supercooling threshold formula

The hydrology of subglacial overdeepenings: A new supercooling threshold formula

Overdeepenings are a hallmark glacial landform of broad geomorphologlogical and glaciological interest. Their formation mechanism has not yet been fully uncovered, but subglacial drainage is likely a key factor. One prominent hypothesis states that the depth of an overdeepening stabilizes at the sup...

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Bibliographic Details
Published in:Geophysical research letters Vol. 43; no. 5; pp. 2045 - 2052
Main Author: Werder, Mauro A.
Format: Journal Article
Language:English
Published: Washington John Wiley & Sons, Inc 16-03-2016
Subjects:
Depth
Drainage
Drainage systems
Formulas (mathematics)
Geomorphology
glacial erosion
Glaciation
Glaciers
Glaciohydrology
Hydrologic models
Hydrology
Hydrostatic pressure
Hypotheses
Ice
Ice sheets
Landforms
Mathematical models
Mountain glaciers
overdeepening
Sheets
Shutdowns
Slopes
Stabilizing
subglacial hydrology
Supercooling
Thresholds
Two dimensional models
Water pressure
Water surface slope
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Summary:Overdeepenings are a hallmark glacial landform of broad geomorphologlogical and glaciological interest. Their formation mechanism has not yet been fully uncovered, but subglacial drainage is likely a key factor. One prominent hypothesis states that the depth of an overdeepening stabilizes at the supercooling threshold. This threshold is reached when the adverse bed slope terminating an overdeepening is sufficiently large to shut down the efficient, channelized drainage system. Classic theory puts this threshold at a ratio of bed to surface slope of −1.6. Here I extend that theory by taking into account that downstream water pressure can be below overburden pressure. The new formula agrees well with results from one‐ and two‐dimensional subglacial drainage models. Applying it to observations of 147 overdeepenings from alpine glaciers and ice sheets shows that the depth of overdeepenings rarely exceeds the new supercooling threshold. Thus, this work supports the stabilizing hypothesis. Key Points An improved supercooling threshold formula for subglacial overdeepenings is presented The formula is validated against subglacial drainage system simulations Application to overdeepenings supports hypothesis that depth is limited by supercooling threshold
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ISSN:0094-8276
1944-8007
DOI:10.1002/2015GL067542