- 1CNRS, ISTerre, Grenoble, France (noelie.bontemps@univ-grenoble-alpes.fr)
- 2CNRS, ISTerre, Grenoble, France (eric.larose@univ-grenoble-alpes.fr)
- 3Géoazur, Université Côte d'Azur, Sophia-Antipolis, France (malgorzata.chmiel@geoazur.unice)
- 4ONF-RTM, Grenoble, france (antoine.blanc@onf.fr)
The hamlet of La Bérarde, a touristic hotspot in the French Alps for hiking and mountaineering and an iconic site in the history of alpinism, was severely impacted by the catastrophic flooding of the Etançons torrent during the night of June 20–21, 2024. The event resulted in the evacuation of 114 people, affected 66 buildings, and resulted in the complete destruction of 16 structures. The flood, characterised afterwards with a centennial recurrence interval, was caused by a combination of intense precipitation over the 2 days, significant snowmelt, and the sudden drainage of the supraglacial lake of the Bonne Pierre glacier.
Field assessments revealed that up to 300,000 m³ of sediments were transported downstream by the torrent, explaining the landscape transformation that occurred in the hamlet. Due to the evacuation of the village during the middle of the night and to the destruction of the river gauge downstream during the event,reconstructing the sequence of events involving the torrent and the associated debris flows proved challenging.
The three closest seismic stations to La Bérarde (located 15-20 km away) were used in this study to better refine the timeline of the flood. Tools such as seismic signal polarisation and spectrograms helped us to constrain the hours of the night where we observed an increase in the recorded seismic energy and a shift in the polarisation toward the hamlet. These findings align with eyewitness accounts and measurements of the Véneon River flow prior to the destruction of the river gauge by the flood.
Eventually, we installed a seismic station shortly after the flood near the front of the Bonne Pierre glacier and at the cross section of the Bonne Pierre river and the Etançons torrent to have a better idea of the sediment’s availability in case of futur glacial lake drainage. This revealed that a large amount of sediment is available and could potentially be carried by the torrent in case of another rapid drainage of the glacier.
This work was funded by the European Research Council (ERC) under grant No. 101142154 - Crack The Rock project.
How to cite: Bontemps, N., Larose, E., Chmiel, M., and Blanc, A.: The June 2024 Flooding of La Bérarde: Insights from Seismic Data and Field Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6557, https://doi.org/10.5194/egusphere-egu25-6557, 2025.
