Millennia-Old Tree Stumps Emerge on the English Channel Beaches as Sea Levels Continue to Rise

Following the winter storms of 2013-2014, peat beds and fossil trunks reemerged along the western coast of Cotentin. These remnants belong to once humid forests that were submerged by the sea’s advance since the last glaciation. Their dating traces the gradual takeover of the shoreline and its contemporary climatic echo.

From Granville to the Lingreville harbor, the 2013-2014 storms uncovered peat dated up to 6,500 years ago

A 2015 synthesis, published in the Bulletin of the Geological and Mineralogical Society of Brittany, inventories these outcrops. According to Brigitte Van Vliet-Lanoë of CNRS at the University of Brest, and her coauthors, the peats reappeared in early 2014 at Saint-Jean-le-Thomas, at Hauteville, at the Lingreville harbor, and on the Fourneau beach at Granville.

Thus, the base of the Lingreville peat would date back to roughly 6,500 years, according to studies from 1973. In Saint-Jean-le-Thomas, in the Mont-Saint-Michel Bay, the peat sequence extends rather from 5,000 to 3,000 years before present.

Oak, hornbeam, and birch were killed by a brackish layer before being sealed under the mud

The scenario described by geologists comprises several stages. First, oaks and hornbeams colonize well-drained soils about 8,000 years ago. Then the freshwater lens rises and a peat bog settles in, overrun by hazel, birch, willows and alders.

As groundwater becomes brackish, the trees gradually wither away. Then reeds and salt-tolerant plants take over. Finally, a marshy silt covers everything and fixes the stumps in a life position.

Thus the wood traverses the centuries in a waterlogged and oxygen-poor environment. Moreover, the acidity of the Cotentin soils slows bacterial activity. Yet, these deposits often combine several episodes separated by erosion phases.

The Quintefeuille forest in Calvados and the Borth forest in Wales follow the same timetable

The phenomenon is not limited to the Channel. For example, on the Bessin coastline at Ver-sur-Mer, trunks of the Quintefeuille forest still appear standing in the peat. In Graye-sur-Mer, a 2020 study in the MNHN’s Naturae journal describes a marsh-swamp forest evolving into a marsh between 5,500 and 3,500 years before present.

According to this work, the sea’s influence is felt there from around 4,000 years ago. Across the Channel, the Borth forest, in Cardigan Bay, dates from roughly 6,000 to 4,500 years ago. Observed as early as 1811, its stumps fed a Welsh legend of a sunken kingdom.

Sea level stood about 120 meters lower 20,000 years ago, and its rise has accelerated over the past century

At the last glacial maximum, the sea stood roughly 120 meters below its present level, according to the Ministry of Culture. Consequently, the melting ice caps progressively drowned the plain that once covered the Channel, before a notable slowdown set in.

However, the rise has gathered pace again. According to the IPCC’s sixth report, the average global ocean level rose by about 20 centimeters between 1901 and 2018. More strikingly, its rate reached 3.7 millimeters per year between 2006 and 2018.

Along the Norman coast, state services note an elevation of 2 to 3 millimeters per year. The Manche Department also indicates that 35% of its natural shores are retreating, compared with 20% nationally. The Lingreville stumps therefore remind us that a shoreline is never fixed.