six months after the flood, experts warn of the risk of recurrence

More than six months after the torrential flood which devastated the hamlet of La Bérarde in Isère, scientists have released their conclusions on the origin of the disaster. According to their report, the risk of recurrence exists.

Six months later, the images are still in everyone’s memory. On June 21, 2024, the hamlet of La Bérarde in Isère was devastated by a torrential flood, taking several houses with it. Miraculously, no casualties were reported. All residents were evacuated in time.

But this disaster left behind many questions. To try to shed light on the reasons for this event, around thirty scientists, under the authority of the mountain land restoration service, carried out studies, the conclusions of which were publicly revealed at the end of December.

These explorations led scientists to analyze the watershed of the Etançons torrent, which largely contributed to the devastating flood of the Vénéon, as well as the Bonne Pierre watershed. And it is in particular the glacier of the same name, located upstream of the hamlet of La Bérarde, which has been the subject of particular attention.

This glacier with its irregular profile promotes water retention. He had been the subject of a report shortly before the disaster, as reported by Alpine Mag. Skiers and mountaineers had declared the presence of a lake on the Bonne Pierre glacier.

Member of the group of scientists mobilized on these studies, Eric Larose, cgeophysicist researcher at the CNRS at the Institute of Earth Sciences (ISTerre-Grenoble), confirms that it is “of a supraglacial lake“who was”known since 2016“. “We try to identify them because in certain cases they drain suddenly, that is to say they will infiltrate under the glacier and drain all the water like a dam burst with flooding downstream.explains Eric Larose.

According to the researcher, there are several hundred supraglacial lakes in the Alps. That of Good Pierre”drained naturally every year, between June and July, it gradually lost its water“, says the researcher.

Thanks to topographical measurements taken on the glacier, scientists estimate the surface area of ​​the lake in 2024 at 14,000 m2 for a volume of around 100,000 m3 of water. But this body of waterdifficult to access“cannot be”easily monitored“.

Beyond the role of the Bonne Pierre glacier, scientists believe that the causes of the disaster are multifactorial. There was also “a lot of rain in June with thunderstorms” as well as a “very significant snow melt at the time of the disaster“, indicates Eric Larose.

The combination of these factors caused an exceptional flood, never before crossed by the Vénéon valley. And this torrential lava brought in its wake large quantities of scree, thus devastating the hamlet of La Bérarde.

“If the lake reforms, an equivalent disaster is possible. We will have to live with the fact that a disaster like this can happen again.”

Eric Larose, geophysicist researcher at CNRS

In their conclusions, the glaciologists, geophysicists and other scientists who authored these studies do not exclude a risk of recurrence in the coming years, with global warming accelerating the melting of snow and episodes of severe weather.

“The lake can now reform. The glacier is still largely poorly known so there are potentially other small pockets of water that may exist. There may be other subglacial channels that have not been explored. We still have a lot of unknowns on this black glacier of Bonne Pierre“, alerts the geophysicist researcher at the CNRS.

Now, it is the turn of the Joint Syndicate of Isère Hydraulic Basins to carry out feasibility studies. The objective is to look at the risks and possibilities of rebuilding the hamlet of La Bérarde and this Vénéon valley, which is now almost at a standstill. A public meeting must be held before the end of the first quarter of 2025 to provide an update on the progress of the studies.