(Hostens) On the charred banks of a lake in Gironde (south-west France) small plumes of smoke escape from the ground, the only sign of a fire still active in the basement, ten months after the gigantic fires last summer.
In three places in the Domaine départemental d’Hostens, in the heart of the Landes de Gascogne forest, this invisible hearth is inexorably consuming the veins of an old lignite mine. The smokers appear and disappear as this young coal ignites by digging chimneys to the surface.
At the edge of Lake Bousquey, tree trunks with charred roots are regularly collapsing and crevasses threaten the path, which is closed to the public. Proof that the beast is still moving: “If someone fell into a hole, he would be burned alive. It would be impossible for him to come out of it, if he were alone, ”warns the mayor of Hostens, Jean-Louis Dartiailh.
In order to circumscribe the hot zones, drones equipped with thermal cameras measured underground temperatures sometimes exceeding 200 degrees.
“The danger is permanent and invisible. It’s like setting foot in a barbecue, in the middle of burning ashes, ”abounds Laurent Salaün, head of the environment department at the Department.
The lakes of the Hostens estate, with beaches lined with pine trees, were laid out in the excavations of an open pit mine that supplied fuel to a power station from the early 1930s until its closure in 1963. In total, more than 14.5 million tons of lignite were mined. There would still be 300,000 underground.
“Unfortunately we do not have precise knowledge of all the lignite veins, nor the experience” of this type of fire, underlines Pascale Got, vice-president of the Department in charge of environmental protection.
Especially since the cartography would be very approximate. At the time of the last surveys, “when the vein was less than two meters thick, we did not count it”, points out the mayor of the town.
In a report submitted to the community at the end of last week, the Geological and Mining Research Bureau (BRGM) also notes a “deficit of precise and recent data on the state of the subsoils” and considers this phenomenon “complex” and “unpublished in France”.
The Atmo Nouvelle-Aquitaine air observatory was commissioned to carry out a study on the toxicity of the fumes released.
Laboratory
Test operations should be carried out soon to try to extinguish the underground blaze.
Because another danger lurks: this incandescent mixture, between peat and coal, could consume the small vegetation and the branches on the ground, while the fire season has only just begun. A few weeks ago, flames covered 600 square meters around Lake Bernadas.
“We must imperatively prevent it from reaching areas of intact vegetation”, underlines the president of the department and of SDIS 33, Jean-Luc Gleyze. “It’s highly likely that the smokers could last for months or even longer,” he admits.
Faced with this invisible enemy, the councilor of the town, responsible for the security of the site, calls for major means. “You have to install pumps in the lake and drown the layer of lignite via trenches or small basins. There aren’t that many other solutions,” he claims, a little wearily.
A “very schematic” solution for Jean-Luc Gleyze who considers “illusory today to be able to extinguish all the fires”.
The situation is all the more problematic as the Hostens estate must change its face to become, as part of the Department’s “Forest” mission, an “open-air laboratory” of biodiversity, according to Ms.me Got.
On the part classified as an integral biological reserve, nature will regain its rights without human intervention. On another, which the Gironde community wanted to deforest before the fires, the agropastoralism of the Landes of yesteryear will reappear.
A nursery “unique in France” will also be created in Hostens, responsible for cultivating species that are resilient to climate change – such as periods of drought favorable to fires.