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| Titel |
Thermal characteristics of permafrost in the steep alpine rock walls of the Aiguille du Midi (Mont Blanc Massif, 3842 m a.s.l) |
| VerfasserIn |
F. Magnin, P. Deline, L. Ravanel, J. Noetzli, P. Pogliotti |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1994-0416
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| Digitales Dokument |
URL |
| Erschienen |
In: The Cryosphere ; 9, no. 1 ; Nr. 9, no. 1 (2015-01-16), S.109-121 |
| Datensatznummer |
250116740
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| Publikation (Nr.) |
 copernicus.org/tc-9-109-2015.pdf |
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| Zusammenfassung |
| Permafrost and related thermo-hydro-mechanical processes are thought to
influence high alpine rock wall stability, but a lack of field measurements
means that the characteristics and processes of rock wall permafrost are
poorly understood. To help remedy this situation, in 2005 work began to
install a monitoring system at the Aiguille du Midi (3842 m a.s.l). This
paper presents temperature records from nine surface sensors (eight years of
records) and three 10 m deep boreholes (4 years of records), installed at
locations with different surface and bedrock characteristics. In line with
previous studies, our temperature data analyses showed that:
micro-meteorology controls the surface temperature, active layer thicknesses
are directly related to aspect and ranged from <2 m to nearly 6 m,
and that thin accumulations of snow and open fractures are cooling factors.
Thermal profiles empirically demonstrated the coexistence within a single
rock peak of warm and cold permafrost (about −1.5 to
−4.5 °C at 10 m depth) and the resulting lateral heat fluxes. Our
results also extended current knowledge of the effect of snow, in that we
found similar thermo-insulation effects as reported for gentle mountain
areas. Thick snow warms shaded areas, and may reduce active layer refreezing
in winter and delay its thawing in summer. However, thick snow
thermo-insulation has little effect compared to the high albedo of snow
which leads to cooler conditions at the rock surface in areas exposed to the
sun. A consistent inflection in the thermal profiles reflected the cooling
effect of an open fracture in the bedrock, which appeared to act as a
thermal cutoff in the sub-surface thermal regime. Our field data are the
first to be obtained from an Alpine permafrost site where borehole
temperatures are below −4 °C, and represent a first step towards
the development of strategies to investigate poorly known aspects in steep
bedrock permafrost such as the effects of snow cover and fractures. |
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