Relationship between the water- and thermal regimes in the active layer above permafrost in steep alpine scree slopes
|
Fig. 1 - Alpine scree slope in summer and winter
|
High mountain regions like the
Alps are affected especially strongly by global warming: besides the well
known wasting of glaciers alpine permafrost is also degrading. The melting
process starts at the earth's surface, so that the active layer (annually
thawing) above alpine permafrost thickens. For steep slopes this means
a heavier unfrozen and thus less cohesive scree layer which therefore
can tend to slide down slope more easily, especially when melting water
acts as a lubricant. It is therefore important to obtain a better understanding
about the hydrothermal processes in the active layer.
Questions
- How do form (snow, ice,
liquid, vapour) and amount of water change over the course of the year
at different soil depths?
- How do the elements of the
water regime as snow and ice melt, rain, infiltration and lateral runoff
affect the temperatures in respect to season and soil depth?
- What role does the water
play for the function of the active layer as a thermal insulator between
atmosphere and permafrost?
- When is the maximum thawing
depth reached, when is the lateral runoff on the permafrost table highest
and how do these parameters affect the slope stability?
Hypothesis
In winter the active layer is frozen completely (Fig. 2). Because of the
insulating effect of the snow
cover above atmospheric temperature fluctuations are strongly attenuated
and delayed. When the snow is melting in spring water infiltrates in the
ground and partly freezes again at the cold rocks' surface. Thereby latent
energy becomes free and the temperature rises abruptly. Part of the water
reaches the permafrost table and there flows laterally down slope. The
near surface ground ice will not start to melt in summer until all the
snow has melted away. Melt- and rainwater percolate quickly through in
the coarse textured ground. However, the permafrost body is mainly impermeable
and carries the water down slope in the underground. When the air temperature
decreases in autumn, the active layer will freeze from the surface as
well as from its base until all the soil water is transformed to ice.
|
|
Fig. 2 - For the hydrothermal regime of the active layer above alpine permafrost
in a steep scree slope (here the example of Muot
da Barba Peider at 2980m a.s.l. above Pontresina
in Engadin snow cover and snow melt
are of decisive importance.
|
Methods
For this project an integrative, three part approach was chosen consisting
of:
- aboratory experiments (effect
of each single impact factor)
- Field measurements (Fig. 3) (complex coaction of diverse factors in the terrain)
- Numerical simulation (verification
of the model's representativeness and transfer of the punctual measurement
results to space)
|
Fig. 3 - Slope parallel section through the test alignment in the field to
measure the ground parameters temperature (thermistors), amount of vapour
(vapour traps), water level above permafrost (ultrasonic probe in piezometer),
lateral slope movement (inclinometer), soil water content (TDR probes) and
amount of liquid water infiltrated into the ground (lysimeter). Click on image to enlarge.
|
Significance
The results of this project will help to improve the estimation of the effect
of climate warming on the thermal state of alpine permafrost and therefore
the danger of potential landslides.
Links
Contact
| Keywords: |
SLF, Schnee, Lawine, Lawinen, Forschung |
