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Monitoring of the Taconnaz ice fall (French Alps) using measurements of mass balance, surface velocities and ice cliff position

Abstract : Glacier de Taconnaz is a hanging glacier in the Mont-Blanc area with an upper accumulation area stretching from Dôme du Goûter (4300 m a.s.l.) down to a wide ice cliff at an altitude of about 3300 m a.s.l., over which flows most of the ice accumulated upstream. During winter, ice blocks breaking off the cliff often trigger off large avalanches constituted of a mixture of snow and ice which can be devastating for the downward inhabited areas in the Chamonix valley as was the case in 1988 and 1999. The approach proposed here is twofold. It first consists of quantifying the flow regime over the accumulation area and consequently the yearly amount of ice falling off the cliff. For this purpose, a network of large stakes was first installed in June 2001 and regularly updated since. From the measured height above surface corrected with time series mass balance of two nearby glaciers, a yearly net mass balance map over the accumulation area has been established and converted into a mean discharge of 1.2 ± 0.3 × 106 m3 year− 1 at the cliff. Moreover, monthly remote topographic surveys of the same stakes provided annual surface velocities, which after some assumptions led to a similar independent amount of discharge. The second part consists of trying to assess the frequency at which the collapses occur from similar monthly topographic measurements of the cliff edge position. Although the time series are still short, a single period of about 180 days seems to control the major ice falls. These data also allow for estimation of ice volumes breaking off which, associated with flow values, could help constraining the frequency of falling events.
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Submitted on : Wednesday, April 15, 2009 - 1:07:57 PM
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Emmanuel Le Meur, Christian Vincent. Monitoring of the Taconnaz ice fall (French Alps) using measurements of mass balance, surface velocities and ice cliff position. Cold Regions Science and Technology, Elsevier, 2006, 46 (1), pp.1 à 11. ⟨10.1016/j.coldregions.2006.05.001⟩. ⟨insu-00375530⟩

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