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| Titel |
Modelling bed overdeepenings for the glaciers in the Himalaya-Karakoram region using GlabTop2 |
| VerfasserIn |
Andreas Linsbauer, Holger Frey, Wilfried Haeberli, Horst Machguth |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250096298
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| Publikation (Nr.) |
 EGU/EGU2014-11795.pdf |
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| Zusammenfassung |
| Calculating ice thickness distribution and bed topographies for large glacier samples is an
essential task to estimate stored ice volumes with their potential for sea level rise and to
model possible future retreat scenarios of glacier evolution under conditions of continued
warming. Modelling such bed topographies to become exposed in the near future by
continued glacier retreat also enables modelling of future landscapes with their landforms,
processes and interactions. As the erosive power of glaciers can form numerous and
sometimes large closed topographic bed depressions, many overdeepenings are commonly
found in formerly glaciated mountain ranges. Where such overdeepend parts are
becoming exposed and filled with water rather than sediments new lakes can come into
existence.
GlabTop (Glacier bed Topography) has been used to model ice thickness distribution and
bed topographies of large glacier samples. It is an ice dynamical approach, based on the
assumption of perfect plasticity of ice, which relates glacier thickness to its local surface
slope via the basal shear stress estimated for each glacier based on an empirical relation
between shear stress and elevation range as a governing factor of mass turnover. From
comparison with radio-echo soundings in the Swiss Alps, the uncertainty range of local ice
thicknesses calculated with GlabTop is estimated at about ±30%. The spatial variability of
ice depths, i.e. the glacier-bed topography, primarily depends on surface slope as provided by
DEMs and is quite robust. For the entire Swiss Alps, GlabTop revealed a considerable
number (more than 500) of (partly large) overdeepenings in the modelled glacier beds with a
total area of about 50-60 km2 and a total volume of about 1.5-2.5 km3. A number
of lakes have formed in such modelled overdeepenings during the past years and
decades.
To calculate bed topographies with their overdeepenings for the 28’100 glaciers of the
Himalaya-Karakoram region the GlabTop-approach was modified and named GlabTop2.
While the original approach relied on so called glacier branch lines that had to be
digitized manually, GlabTop2 is fully automated and requires only a DEM and
glacier outlines as an input. The result is the same: ice thickness distribution and bed
topographies, which can be used for volume calculations and for model simulations
concerning glacier retreat scenarios and future landscapes. According to the model
output there are about 15’000 overdeepenings covering an area of about 2000 km2
and having a total volume of about 120 km3 (3-4% of the now existing glacier
volume) in the Himalaya-Karakoram region. In a statistical analysis concerning the
morphological characteristics of these overdeepenings, mean and maximum values of the
parameters surface area, length, width, depth, volume, frontal/adverse slope and their
statistical interrelations are determined with their corresponding uncertainty ranges and
compared with a corresponding analysis for the Swiss Alps. While the modelled
overdeepenings based on model runs with different data input differ in shape, the locations
of the overdeepenings are robust and the values for the extracted parameters are
comparable. |
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