Ongoing Projects

ACQWA Project (Assessing Climate impacts on the Quantity and quality of WAter)

Modeling gravity-driven instabilities

We model the progressive maturation of a heterogeneous mass toward a gravity-driven instability, characterized by the competition between frictional sliding and tension cracking, using an array of slider blocks on an inclined basal surface, which interact via elastic-brittle springs. The inner material damage occurs via stress corrosion. Three regimes, controlling the mass instability ans its precursory behavior, are classified as a function of the ration Tc/Tf of two characteristic timescales associated with internal damage/creep and frictional sliding.

Spring-block model animations

For T_c/T_f<<1, creep/damage occurs sufficiently fast compared with nucleation of sliding, causing bonds to break, and the bottom part of the mass undergoes a fragmentation process with the creation of a heterogeneous population of sliding blocks. Example of fragmentation regime

For T_c/T_f>>1, the whole mass undergoes a series of internal stick and slip events, associated with an initial slow average downward motion of the whole mass, and progressively accelerates until a global coherent runaway is observed. Example of stick-slip regime

For the intermediate regime T_c/T_f~1, a macroscopic crack nucleates and propagates along the location of the largest curvature associated with the change of slope from the stable frictional state in the upper part the unstable frictional sliding state in the lower part. Example of slab regime

The other important parameter is the Young modulus Y which controls the correlation length of displacements in the system.

Application to Altels

The Altels hanging glacier broke off on September 11, 1895. The ice volume of the catastrophic rupture was estimated at 4.10⁶ cubic meters and is the largest ever observed ice fall event in the Alps. The causes of this collapse are however not entirely clear. Based on previous studies, we reanalyzed this break-off event , with the help of the model described above. The simulations indicate that a break-off event is only possible when the basal friction at the bedrock is reduced in a restricted area, possible induced by the storage of infiltrated water within the glacier. Moreover, our simulations reveal a two-step behavior: (i) A first quiescent phase, without visible changes, with a duration depending on the rate of change in basal friction; (ii) an active phase with a rapid increase of basal motion over a few days. The general lesson obtained from the comparison between the simulations and the available evidence is that visible signs of the destabilization process of a hanging glacier, resulting from a progressive warming of the ice/bed interface towards a temperate regime, will appear just a few day prior to the break-off.

Example of a simulation