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| Titel |
Climate warming and stability of cold hanging glaciers Lessons from the gigantic 1895 Altels break-off |
| VerfasserIn |
Jerome Faillettaz, Didier Sornette, Martin Funk |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250050941
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| Zusammenfassung |
| The Altels hanging glacier broke off on September 11, 1895. The ice volume of this
catastrophic rupture was estimated to 4.106 cubic meters and is the largest ever observed ice
fall event in the Alps. However, the causes of this collapse are not entirely clear. Based on
previous studies, we reanalyzed this break-off event, with help of a new numerical model.
This model, initially developed by Faillettaz et al. (2010) for gravity-driven instabilities, was
applied to this glacier. It takes into account the progressive maturation of a heterogeneous
mass towards a gravity-driven instability, characterized by the competition between frictional
sliding and tensile cracking. We use an array of sliding blocks on an inclined (and
curved) basal surface, which interact via elastic-brittle springs. A realistic state- and
rate-dependent friction law is used for the block-bed interaction. We model the evolution
of the inner material properties of the ice and its progressive damage eventually
leading to failure, by means of a stress corrosion law governing the rupture of the
springs.
It appeared that such a break-off event could only happen when the basal friction at the
bedrock is reduced in a restricted area, possibly induced by the storage of infiltrated water
within the glacier. This result seems to be confirmed by the hot summers prior to the
collapse. Moreover, a two-step behavior could be evidenced: (i) A first quiescent phase,
without visible changes, with a duration depending on the rate of basal changes.
(ii) An active phase with a rapid increase of basal motion within a few days. As a
consequence, a crown crevasse opens within a few days (which was observed) prior the
final collapse. This means that the destabilization process of a hanging glacier due
to a progressive warming of the ice/bed interface towards a temperate regime is
expected to occur without easily visible signs until a few days prior to the break-off
event.
In a more general context, global climate warming may influence the stability
of cold hanging glaciers. As the rupture process takes some time to develop and
external precursors are only visible shortly before the break-off, some hanging
glacier still, at least partially, frozen to the bedrock may currently be in an unstable
phase.
References
[1]Â Â Â Faillettaz, J., Sornette, D. and
Funk, M. (2010). Gravity-driven instabilities: interplay between state-and-velocity
dependent frictional sliding and stress corrosion damage cracking. J. Geophys. Res.,
115, B03409, doi:10.1029/2009JB006512. arXiv/0904.0944. |
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