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| Titel |
Middle Holocene landslide cluster in the south-western Alps: Results from cosmic ray exposure dating of numerous large-scale gravitational failures |
| VerfasserIn |
S. Zerathe, T. Lebourg, R. Braucher, D. Bourlès |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250067418
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| Zusammenfassung |
| Nowadays, it is formerly assumed that the internal structure of a slope (e.g. lithology and
rock mass properties, inherited faults and heterogeneities, etc.) acts as the main preparatory
factors for the progressive development of large-scale landslides. However, debates
are still ongoing to argue if pointing out some triggering factors, responsible for
final slope failures, is possible (amongst them are glacial debuttressing, seismic
activities or climatic changes), and especially when considering landslide cluster at an
orogen-scale. In the central and eastern Alps, a middle Holocene period (~4 ka BP)
of increased mix-pattern of landslide activity is now identified by many authors
(Prager et al, 2008; Sanchez et al, 2009; Borgatti and Soldati, 2010). In this study, we
highlight a new spatial and temporally concordant cluster of deep-seated slope
failure in the external south-western Alps and we attempt to argue and review the
possible causes for such wide-spread slope instabilities at both local and larger
scale.
High resolution field mapping coupled with electrical resistivity tomography allow
defining the structural model of the deep-seated landslides (DSLs), their depth limit (100 to
200 m depth) and their involved rock volume (>107 m3). We show that they developed
strictly in the same geostructural context, such as thick mudstone layers overlain by faulted
limestone. They followed a block-spread model of deformation that could evolve in
rock-collapse events (Zerathe and Lebourg, 2011).
Cosmic Ray Exposure dating, using both 36Cl and 10Be in coexisting limestone and chert,
respectively, have been carried out from the main scarps of six DSLs. All the chronological
data measured are in the range of 3 to 4.5 ka. They highlighted: (i) mainly single and fast
ruptures and (ii) their concomitant initiation with two main peaks of activity at around 3.2
and 4.1 ka.
Because this region was not affected by historical glaciations events, landslide triggering
by glacial unloading can be excluded. Our combined data along with field observations
preferentially suggest that these failures were climatically driven and where controlled by
high pressure changes in the karstic medium. Despite requiring further investigations
and discussions, it appears that, based on the numerous dated events during this
middle Holocene period, a potential large-scale triggering cannot be excluded in this
area.
Prager C., Zangerl C., Patzelt G. and Brandner R. (2008) Age distribution of fossil
landslides in the Tyrol (Austria) and its surrounding areas. Nat. Hazards Earth Syst. Sci. 8,
377-407.
Sanchez G., Rolland Y., Corsini M., Braucher R., Bourlès D., Arnold M. and Aumaître
G. (2009) Relationships between tectonics, slope instability and climate change: Cosmic ray
exposure dating of active faults, landslides and glacial surfaces in the SW Alps.
Geomorphology 117, 1-13.
Borgatti L. and Soldati M. (2010) Landslides as a geomorphological proxy for
climate change: A record from the Dolomites (northern Italy). Geomorphology 120,
56-64.
Zerathe S. and Lebourg T. (2011) Evolution stages of large deep-seated landslides at the
front of a subalpine meridional chain (Maritime-Alps, France). Geomorphology 138 (2012)
390–403. |
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