Erosion of the central Swiss Alps

Erosion of the central Swiss Alps The quantification of the rates and processes of erosion is a principal challenge in advancing our understanding of the mechanics of mountain building. The European Alps are a key site due to the wealth of geologic and geodetic data that have been obtained in this orogen. Figure 1 shows river basins in the Central and Eastern Alps in which we have determined erosion rates (Refs. 1 and 2). We used the rare cosmogenic isotope Beryllium-10 (10Be) in ~50 quartz samples from river sediment. The technique averages denudation (the sum of chemical weathering and physical erosion) over the time it takes to erode 60 cm of the Earth`s surface and integrates all erosion processes in the entire river catchment. Thus, the integration time scale is different depending on the prevailing erosion rate (see Fig. 2 and Ref. 3).

We find that denudation rates vary between 0.2 and 2.0 mm/yr in the Swiss Central Alps. Denudation rates are highest where altitude is highest, slopes are steepest, and the Earth´s crust is thickest (Fig. 3). In the Swiss Central Alps, denudation rates also correlate with rock uplift rate as measured by leveling. As major plate convergence is absent in the Alps, we explain this correlation with an isostatic response to erosion: the faster the mountain chain erodes, the faster it is lifted up. Hence uplift is a consequence of erosion, not its cause (Ref. 4).

We have also found very low (0.03 – 0.1 mm/yr) denudation rates in soils from the highest and steepest soil-mantled hillslopes in the Swiss Central Alps (Fig. 4, Ref. 5). Yet catchments from these areas also contain sediment that was eroded at much higher rates. We explain the high rates exceeding those at which soil is eroded as being accelerated by addition from landslides, rock falls, and debris falls. These erosion processes only occur in high, glacially oversteepened mountain belts. We suspect that the nature of this binary mixture of erosion processes sets the rates in all high, steep mountain belts were such fast erosion takes place on non-soil mantled hillslopes.

Geology of the Swiss Central Alps

Fig. 1: (Top: Geology of the Swiss Central Alps and sampled rivers for cosmogenic nuclide analysis (outlined in black). Bottom: Map with respective denudation rates in mm/kyr and recent uplift rates in mm/yr, with underlying lithological map; Fig. from Norton et al., 2011.

Fig. 2: Time scale, over which erosion rates from cosmogenic nuclides integrate. This is called „apparent age“ and is the time needed to erode 60 cm of the upper Earth´s surface (from von Blanckenburg, 2005, EPSL).

Fig. 3: Denudation rate, mean topographic Altitude, recent rock uplift, and orogenic depth of the Swiss Central Alps (Fig. modified from Wittmann et al., 2007).

Fig. 4: Denudation rates in the Goms: Open symbols represent low denudation rates measured in soils of non-glacially modified catchments, whereas colored (blue and green) symbols represent high to very high denudation rates measured in glacially-modified basins that are prone to stochastic mass wasting processes (Fig. modified from Norton et al., 2010).

 

References:

1 Wittmann, H., von Blanckenburg, F., Kruesmann, T., Norton, K.P., Kubik, P.W., 2007. Relation between rock uplift and denudation from cosmogenic nuclides in river sediment in the Central Alps of Switzerland. Journal of Geophysical Research-Earth Surface. 112. 

2 Norton, K.P., von Blanckenburg, F., Schlunegger, F., Schwab, M., Kubik, P.W., 2008. Cosmogenic nuclide-based investigation of spatial erosion and hillslope channel coupling in the transient foreland of the Swiss Alps. Geomorphology. 95, 474-486.

3 Champagnac, J.-D.; Schunegger, F.; Norton, K.; von Blanckenburg, F.; Abbühl, L. M.; Schwab, M. (2009): Erosion-driven uplift of the modern Central Alps. Tectonophysics, 474, 1-2, 236-249.

4 Norton, K. P.; von Blanckenburg, F. (2010): Silicate weathering of soil-mantled slopes in an active Alpine landscape. Geochimica et Cosmochimica Acta, 74, 18, 5243-5258.

5 Norton, K. P.; von Blanckenburg, F.; Kubik, P. W. (2010): Cosmogenic nuclide-derived rates of diffusive and episodic erosion in the glacially sculpted upper Rhone Valley, Swiss Alps. Earth Surface Processes and Landforms, 35, 6, 651-662.

6 Norton, K. P.; von Blanckenburg, F.; DiBiase, R.; Schlunegger, F.; Kubik, P. W. (2011): Cosmogenic 10Be-derived denudation rates of the Eastern and Southern European Alps. International Journal of Earth Sciences, 100, 5, 1163-1179.

Contact

Profile photo of  Dr. Hella Wittmann-Oelze

Dr. Hella Wittmann-Oelze
Geochemistry of the Earth's surface

Telegrafenberg
Building E, room 228
14473 Potsdam
tel. +49 331 288-2820