The Dune of Pilat, a massive shifting landform, is slowly consuming WWII blockhouses and reshaping the coastal landscape of France.
Dune of Pilat's size and movement
The dune of Pilat, rising to 103.6 meters and containing 55 million cubic meters of sand, moves 1 to 5 meters per year toward the maritime pine forest. This gradual shift has caused World War II blockhouses, built on the dune, to be displaced 200 meters away, some now submerged under 15 meters of water.Location and comparison
The dune spans 616 meters from west to east and 2.9 kilometers from north to south, at the southern entrance of the Arcachon Basin in the commune of La Teste-de-Buch. Local comparisons suggest its volume is equivalent to 22,000 Olympic swimming pools, far surpassing the 13 million cubic meters of concrete used in the Atlantic Wall.Formation and historical context
The dune's formation dates back to the Flanders transgression, a period of rising sea levels that pushed sandbanks from the continental shelf eastward, creating today’s beaches and dunes. Earlier, smaller dunes held back marshes and ponds, which were later buried by larger parabolic dunes.Impact on the pine forest
The dune’s movement affects the maritime pine forest, planted in the 18th century by Nicolas Brémontier to stabilize the coastal dunes. Wind continues to drive sand from marine banks like the Arguin Bank, depositing it on the beach and allowing the dune to advance eastward, gradually encroaching on the forest.Effects on blockhouses
Marc Robin, a coastal risk specialist, explains that the dune’s movement impacts structures built on it. Blockhouses from the Atlantic Wall, originally resting on sand, have tilted or slid as the sea erodes the foundation, causing them to shift or fall toward the dune’s base.Displacement and coastal erosion
The dune’s migration toward the land displaces blockhouses from its crest, a process similar to measuring coastal erosion. This phenomenon is not unique to Pilat, as many blockhouses along the Aquitaine coast are now buried on the beach or submerged, far from their original positions on the dunes.Underwater structures and marine life
Some blockhouses are now underwater, serving as artificial reefs for marine life. Others remain on the beach, covered in graffiti, while a local editor describes the submerged Gaillouneys battery as the most spectacular diving site on blockhouses in Europe.Tourism and visitor numbers
The dune attracts more than 10,000 visitors on certain August days, making it the most visited site in Gironde and one of the most visited natural sites in France. Visitors often encounter blockhouses on the beach without actively seeking them, as the dune’s summit offers a panoramic view of the landscape.Inconsistent measurements and data
Some sources cite varying figures, such as a height of 106.6 meters or 60 million cubic meters of sand, and claim two blockhouses have been displaced by 250 meters. These discrepancies likely result from different dates and measurement methods, as the dune’s shape changes constantly with the wind.
