Sonntag, 3. Mai 2009

Springtime = landslide time

The abundant snow falls in the winter 2008-2009 in the Alps are now melting since March 2009, and until now have provided hughe amounts of melt water. This water not all run off, but also provide restocking of the groundwater reservoir, in fact the groundwater levels now are the highest measured in the last years.

But water can also trigger failure of rock or earth masses by reducing the friction between layers or other discontinuities, that can then become the surface of rupture for a landslide.

This is an example that occured two weeks ago, destroying a bridge between a village and some smaller farms.

In this case, a small creek provided melt water, that infiltrated in a older earthflow (creep), consisting of reworked argilleous material and debris, resting on an alternation of marls and sandstones. Also the creek eroded the orographic right flank of the relict earthflood.
On the orographic left flank, the scarp of the recent landslide, representing the surface of rupture, follows the general dip of the strata (dipping southeast).

Notable are also older scarps, with abundant vegetation, that rappresent older movements and failures of the landslide.

The landslide generated also a debris flow, that following the creek deposited the landslide material in a delta at the end of the gorge of the creek, and subsequently damming up a larger river feed by the smaller creek.

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