| Summary: | As sediment conveyors, rockglaciers - and more generally the creep of perennially frozen ground may be the source of slope instability processes (e.g. rock falls, debris flows) on steep valley sides in a mountain environment. Any change in the rate of permafrost creep is susceptible to affect both the frequency and magnitude of related slope instabilities. There is currently an increasing interest in the densely inhabitated European Alps to document the behaviour of the high-altitude permafrost environment. Studies on rock glacier dynamics have shown that three superimposed types of temporal variability in surface motion can be envisaged at a secular scale: a seasonal rhythm, changes in annual mean velocities, a decadal to pluri-decadal trend. The present contribution compares and analyses the variations in annual velocities that have been observed at the surface of rock glaciers in the European Alps since 2002/03. It represents a pioneer attempt to synthesize the annual variations of rockglaciers activity at this scale. Short-term changes in surface motion of rockglaciers have been monitored in the European Alps since a few years by several research groups, mostly by means of real time kinematics GPS or geodetic survey using a total station. Annual series have been acquired between 2002/03 and 2006/07 on more than 13 rockglaciers located in different parts of the alpine arc. The provided dataset is analysed paying regard especially to two extreme warm climatic events that affected the European alpine region during the 2003-2007 period: the heat wave of summer 2003 and the 2006-07 warm swell, namely a 15-month period of quasi continuous large positive temperature anomaly between April 2006 and June 2007. Despite different size, morphology, ice content, complexity of flow field, mean annual velocity, seasonal rhythm, etc., the compared rockglaciers have surprisingly shown so far a rather homogeneous and synchronous behaviour since 2003: most of them reached a maximal rate of activity in 2003/04 before that their horizontal velocity dropped drastically in 2004/05 and 2005/06. First results in 2006/07 indicate, at least in the western Swiss Alps, a stabilisation or even a slight increase of velocities. The relative range of variation has reached 20 to more than 50 % in one or two years. The absolute range of variation is much larger for rapidly moving rock glacier. Interannual changes appear to be well related to mean annual ground surface temperature shifts with a delay of approximately 6-12 months reflecting their propagation deeper into permafrost.
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