PETIT VELAN (VS)
Active rock glacier, partly destabilized
Elevation: 2520-2820m - Massif: Valais Alps (Grand-Combin) - Commune: Bourg-Saint-Pierre (VS)
The Petit Vélan rock glacier may be considered as partially destabilized since around 1995. Following the opening of a transversal crevasse about 200m above the front, the terminal tongue was gradually separating itself from the main rock glacier body and started to move at several meters per year. Annual velocity measurements of the rock glacier have been carried out by GNSS since 2005.
Measurements and observations
Thermal (ground surface temperature : GST)
Geophysics (electrical resistivity)
Destabilized Petit Vélan rock glacier (September 2007).
Longitudinal (T01) and transversal (T10) electrical resistivity tomography profiles.
Measured horizontal flow field (mean annual velocity).
Annual horizontal surface velocity in both intact and destabilized sections of the rock glacier. Mean of a selected set of points.
Mean annual ground surface temperature. The orange curve represents the mean temperature of the n sensors installed on the site (grey curves). The orange dotted line is the mean temperature observed on the site since the beginning of the measurements.
Contribution of the annual Ground Freezing (sum of all daily mean values < 0°C) and Ground Thawing (>0°C) Indexes to the mean annual ground surface temperature (MAGST) on a set of selected locations (n) on the site. Or : how cold was the winter and how warm was the summer at the surface of the ground ?
Annual dates of the start and end of the snowmelt period (zero curtain phase). Mean of n sensors placed on permafrost terrain. The dotted lines show the mean dates since the beginning of the time series.
Delaloye R. & Morard S. (2011). Le glacier rocheux déstabilisé du Petit-Vélan (Val d'Entremont, Valais): morphologie de surface, vitesses de déplacement et structure interne. La géomorphologie alpine: entre patrimoine et contrainte. Actes du colloque de la Société Suisse de Géomorphologie, 3-5 septembre 2009, Olivone (Géovisions n° 36). Lausanne: Université, Institut de Géographie. (pdf)
Delaloye, R., Lambiel, C. and Gärtner-Roer, I. (2010). Overview of rock glacier kinematics research in the Swiss Alps. Seasonal rhythm, interannual variations and trends over several decades. Geographica Helvetica, 65/2, 135-145. DOI: 10.5194/gh-65-135-2010