This study uses electrical resistivity tomography (ERT) surveys over 20 years to characterize underground flows near the Lascaux Cave in France. Cluster analysis identified an area (cluster 10) where resistivity variations correlated strongly with climatic conditions, suggesting it is the recharge area for flows measured in the cave. ERT is proposed as a sustainable monitoring method to help control runoff and prevent infiltration issues.

1. This analysis taking into account the resistivity data of all the 20 ERT surveys, trying to
highlight area with different type of variations.
The layers 1 to 4 are filtered.
Noticed that the cluster 10 covers the area which varies similarly with the climatic condition.
How to Characterize a Recharge Area by ERT Time Lapse and
Cluster Analysis ? - Application to Lascaux Cave
Shan XU, Colette SIRIEIX, Joëlle RISS and Philippe MALAURENT
I2M, CNRS UMR 5295, University of Bordeaux, France
20th European Meeting of Environmental and Engineering Geophysics, 15-17 Sept 2014, Athens, Greece
Introduction
This study focuses on the application of geophysical methods over a decorated cave in the prehistoric site Lascaux. The Lascaux cave located in the south-eastern part of the
department of Dordogne (24, France) is a cave which is considered as one of the most important prehistoric caves worldwide. It’s necessary to recognize the water flow to take
control of the role of water of the preservation of Lascaux cave.
The non-invasive/destructive geophysical techniques are used to preserve and avoid disturbance of culturally sensitive paintings in the cave. Thus, the Electrical Resistivity
Tomography (ERT) has been established to characterize the underground flows. This work presents the results of a temporal monitoring carried out by ERT.
The cave is under surveillance by an in-situ control
center which records continually all types of data that
may cause an influence of conservation of the cave.
Acknowledgements
We wish to thank French Ministry of Culture and Communication
(Regional Direction of Cultural Affairs of Aquitaine) for their collaboration
in this study.
Shan XU, contact e-mail : shan.xu@u-bordeaux.fr
lascaux.culture.fr
The four zones are empirically determined based on
the specific resistivity varying with climatic conditions.
Their edge is at first chosen manually.
Zone I - large variation of resistivity
Zone II - ‘stable’ : vary little over time
Zone III - variation lies on the climatic condition
Zone IV - a resistant area
Relative variation of the
resistivity before and
after the correction of
temperature is less
than ±15% under the
4th layer (1.06 m).
-30%
-20%
-10%
0%
10%
20%
30%
0 5 10 15 20
%changeofresistivity
Depth (m)
Conclusion and perspectives
The ERT surveys have highlighted an area in which the resistivity varies with the change of the flow
rate. The resistivity change of this area is well correlated with the flow rate measured in the cave and
seems to increase or decrease just before change of the flow rate. So this area could probably be the
recharge zone of the flow measured in the cave. The areas which have a different way of the
resistivity change have been put in evidence by an ascendant hierarchical cluster analysis. We
consider that a Time-lapse ERT installed in a sustainable way is a method that could help control and
prevent the runoff into the cave together with the effective infiltration.
Geological context The cave and ERT survey location Resistivity model after temperature correction
Climatic data
Cluster analysis
Analysis results