Spatio-temporal variations of rockfall activity at Täschgufer (Valais Alps)

Rockfall activity at Täschgufer has been assessed with two different approaches and included 270 cross-sections of 18 juvenile and 564 increment cores from 135 adult larch trees (Larix decidua Mill.). The reconstruction covered more than four hundred years (16002002) and furnished data on 741 rockfall events. Spatial analyses clearly showed that rockfall continuously occurred on the slope in the past in the form of high frequency, low magnitude events. In contrast, one large magnitude rockfall could be dated to A.D. 1720, which removed most trees of the stand located in the southern part of the slope. Data further show that the forest recolonizing the slope after the event gradually improved its protective function, reducing the rate of reconstructed rockfall activity by a factor of 13 between the 1740s and 1990s.

The analysis of cross-sections and micro-cuts provided data on the seasonal timing of rockfall activity, indicating that rockfall is scarce during the vegetation period (12%), which locally lasts from early June through mid October. In contrast, 88% of the impacts occur during the winter dormancy of trees between mid October and the end of May. Direct observations on the slope confirm the results, indicating that rockfall activity would be highest around April and May.

Contact : Markus Stoffel

Publications :

Stoffel, M. (2006): A review of studies dealing with tree rings and rockfall activity: The role of dendrogeomorphology in natural hazard research. Natural Hazards 39(1), 51-70. [PDF]

Stoffel, M. & Perret, S. (2006): Reconstructing past rockfall activity with tree rings: some methodological considerations. Dendrochronologia 24(1) 1-15. [PDF]

Stoffel, M., Lièvre, I., Monbaron, M. & Perret, S. (2005): Seasonal timing of rockfall activity on a forested slope at Täschgufer (Valais, Swiss Alps) a dendrochronological approach. Zeitschrift für Geomorphologie 49(1): 89106. [PDF]

Stoffel, M., Schneuwly, D., Bollschweiler, M., Lièvre, I., Delaloye, R., Myint, M. & Monbaron, M. (2005): Analyzing rockfall activity (1600-2002) in a protection forest a case study using dendrogeomorphology. Geomorphology 68 (34): 224241. [PDF]

Stoffel, M. (2005): Spatio-temporal analysis of rockfall activity into forests results from tree-ring and tree analysis. PhD thesis. Department of Geosciences, Geography, University of Fribourg, Geofocus 12: 1-188. [PDF]