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| Titel |
Changes in borehole temperatures, ice content and creep velocities - results from 10 years of monitoring mountain permafrost in Switzerland |
| VerfasserIn |
Jeannette Noetzli, Daniel Vonder Muehll |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250043462
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| Zusammenfassung |
| The network for permafrost monitoring in Switzerland (PERMOS) has been built up since the
early 1990s aiming to document the state and changes of mountain permafrost on a long-term
basis. Following a 6 year pilot-phase starting in 2000, the PERMOS network is now funded
and integrated into the national and international monitoring structures. The observations are
based on three elements: (1) ground temperatures measured in boreholes and at the surface
near to the drill site, (2) changes in subsurface ice and water content at the drill sites by
geo-electrical surveys, and (3) velocities of permafrost creep determined by geodetic
surveys and/or photogrammetry. In addition, standardized documentation of fast
mass movements from permafrost areas (e.g., rock fall) is being established. In this
contribution, we present measurement results of all observation parameters and their
joint interpretation, along with a short overview on PERMOS and its monitoring
strategy.
The connection between air temperatures and permafrost temperatures is not straightforward.
Effects of winter snow conditions, surface cover (cooling effects by coarse blocks),
subsurface ice content (effects of latent heat), and steep topography mask changes in
atmospheric conditions when they propagate into the subsurface. The signal is additionally
delayed by the high thermal inertia of the system. This can explain why temperature time
series from 24 boreholes of up to 20 years length do not (or not yet) reflect a clear warming
signal. Seasonal variations in air temperatures and snow conditions, however, are well
visible in active layer thicknesses in most boreholes, with the intensity of the signal
depending on site characteristics. The information gained from borehole temperatures
is complemented by geo-electrical surveys. Results can be linked to changes in
frozen and unfrozen water content, indicate substantial degradation of ground ice,
and show the potential of a combined approach compared to thermal monitoring
alone.
Kinematics results show an increase of creep velocities or even a destabilization of rock
glaciers in the past years or decades. In view of the borehole measurements, this acceleration
may be related to changes in water content or availability. The inventory of rock falls
comprises more than 150 events from permafrost regions, with an increase of events in the
past two decades. This is likely a result of a combination of factors: growing human activities
in high mountain regions, raised public and scientific awareness to this phenomena, and an
increase of such events. |
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