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Titel |
The current deglaciation of the Ortles-Cevedale massif (Eastern Italian Alps): impacts, controls and degree of imbalance |
VerfasserIn |
L. Carturan, R. Filippi, R. Seppi, P. Gabrielli, C. Notarnicola, L. Bertoldi, F. Paul, P. Rastner, F. Cazorzi, G. Dalla Fontana |
Konferenz |
EGU General Assembly 2012
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 14 (2012) |
Datensatznummer |
250066068
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Zusammenfassung |
The Ortles-Cevedale is the largest glacierized mountain group of the Italian Alps
hosting 112 ice bodies, with a total area of 76.8 km2. Since the 1980’s, this massif is
undergoing a rapid deglaciation, as most of the mountain ranges in the European
Alps. The aims of this work were: i) to quantify area and volume change of the
Ortles-Cevedale glacier system from the 1980s to the 2000s; ii) to improve the knowledge
of factors controlling the spatial variability of the deglaciation; and iii) to assess
the degree of imbalance of individual glaciers with respect to the present climate
conditions.
Two inventories were created, based on Landsat5 TM scenes of 20-09-1987 and
31-08-2009. Contrast-enhanced composites (bands TM5, TM4 and TM3), aerial photos and
field surveys (for the most recent period) were used to correct the automatic delineation of
glaciers derived from a hard classification based on a threshold applied to a TM3/TM5 ratio
image. Since Landsat scenes were acquired at the end of the ablation seasons and fresh snow
was absent, the accumulation areas could be roughly determined by mapping the snow
covered area. This region was identified from the difference in reflectance between snow and
ice in the near infrared band of Landsat (TM4), and mapped after correcting topographic
effects to determine surface reflectance. The area-averaged geodetic mass budget was then
calculated for the individual glaciers by differencing two Digital Terrain Models (2000s
minus 1980s, derived from LiDAR and aerial photogrammetry) and combining the result
with the glacier outlines. Afterwards, we examined the mass balance data using
statistical analyses (Correlation matrices, Principal Component Analysis, Cluster
Analysis). This allowed us highlighting clusters of glaciers, which exhibit a similar
behavior, identify the outlayers and the relative influence of the factors controlling
spatial variability of the mass losses. Finally, we assessed the degree of imbalance of
individual glaciers by comparing the current Accumulation Area Ratios (AAR) with the
balanced-budget AAR (AAR0), the latter also accounting for the debris cover of
glaciers.
We found that the total area loss of the Ortles-Cevedale glaciers from 1987 to 2009
amounts to 23.5 km2, i.e. 23.4% of the initial area. On the other hand, the AAR of the entire
glacier system was 0.3 in both investigated years. The overall debris cover increased from
10.5% to 16.3%. The geodetic mass balance rate was -0.7 m w.e. y-1(as an average on 112
ice bodies), ranging from -0.1 to -1.7 m w.e. y-1. We also found that the main controls of
the differing change of single glaciers are related to their hypsometry (elevation
range and slope), AAR, feeding source and debris cover. Interestingly, a significant
correlation was found between AAR, AAR0 and debris cover. This information was used
to assess and visualize the needed additional reduction of individual glaciers to
reach equilibrium with the current size of their accumulation areas. This amounts
on average to a further reduction of ~40% of the current areal extent of glaciers. |
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