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| Titel |
A Stacked aquifer system controlling the Vence landslide site (French Alps) revealed by hydrogeophysical surveying |
| VerfasserIn |
Sebastien Loock, Thomas Lebourg, Swann Zerate |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250035273
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| Zusammenfassung |
| Since 2006, a temporal imagery of water circulation in a landslide was conducted by an
Electrical Resistivity Tomography (ERT), rainfalls records and a piezometric survey to
quantify the coupling between groundwater supply and circulation and landslide
displacements recorded by tiltmetry since 2009.
This work is based on a multi-scale experimental approach applied on the “Vence”
landslide (South-eastern France, Mediterranean climate) which is characterised by a
sandy-clay sliding mass of Lower Eocene. It is considered as a translational landslide
including 1.2Ã106m3 of material. This landslide affects an inhabited area about 250 m large
by 350 m long, with an average slope of 12Ë /14Ë . The present day landslide activity is
underlined by a variety of failure surfaces appearing in the landscape morphology: tension
cracks, scarps, disorders affecting human activity and particularly the deviation of the
“Lubiane” river at the foot of the slope.
The interpretation of the ERT profiles correlated with the field information confirm us the
presence of the sliding surface towards 12 m depth i.e. at the contact between sliding sands
and clays of Lower Eocene and Cretaceous calcareous formation. Moreover, ERT
profiles display, under the sliding plane, vertical “pits” with low resistivity, i.e.
groundwater circulation, in the calcareous formation. Their occurrences on each
ERT profiles were interpreted as NW-SE fault zones, typical of the regional fault
network.
After each precipitation, the piezometric level in the sandy-clay sliding aquifer increases
gently (of the order of some cm in few days) except in December 2006, January 2008 and
February 2009 where the water table increased around 150cm in few days accompanied with
the strongest tiltmetric variations in 2009 and then fluctuated gently again after
each precipitation. Thus the groundwater in the sliding aquifer comes from two
different origins: (1) direct infiltration from precipitation on the aquifer explaining the
gentle water table response and (2) groundwater overflowing from the deeper karstic
aquifer hosted in the fissured and faulted calcareous formation. This deeper aquifer
is attempted to be filled during autumnal precipitations till it overflowed around
December and February (depending on precipitations) in the upper sliding aquifer.
This groundwater rising will be facilitated by the occurrence of the fault zones
revealed by the low resistivity “pits” on ERT profiles and thus explaining the fast
increases in the water table measured in the sliding aquifer and the important tiltmetric
variations.
The Vence landslide is a case study where two aquifers will evolve separately
except during winter where they will communicate. At this time, the lower aquifer
will overflow in the upper one so to increase quickly the piezometric level and
consequently the tiltmetry triggering the paroxysm in the landslide displacement. |
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