Evidence of multiple thermokarst events in northeastern France and southern Belgium during the two last glaciations. A discussion on ‘Features caused by ground ice growth and decay in Late Pleistocene fluvial deposits, Paris basin, France’ (Bertran et al., 2018)

• Published in: Geomorphology
• Main Authors: van Vliet-Lanoë, Brigitte, Pissart, Albert, Baize, Stephane, Brulhet, Jacques, Ego, Frederic
• Other Authors: Bureau d'évaluation des risques sismiques pour la sûreté des installations (IRSN/PSE-ENV/SCAN/BERSSIN), Service de caractérisation des sites et des aléas naturels (IRSN/PSE-ENV/SCAN), Institut de Radioprotection et de Sûreté Nucléaire (IRSN)-Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Agence Nationale pour la Gestion des Déchets Radioactifs (ANDRA)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2019
• Subjects: Thermokarst; Frost mounds; Orbital forcing; Weichselian; Saalian; Dansgaerd-Oeschger events; [SDU]Sciences of the Universe [physics]; Ice; permafrost; wedge*
• Online Access: https://hal.science/hal-02521595; https://doi.org/10.1016/j.geomorph.2018.08.036

International audience The past thermokarst activities in valleys of northern France and Belgium covered the Upper Weichselian and the Upper Saalian periods. To develop in western Europe, thermokarst first requires an accumulation of ground ice close to the surface progressively stored along the glacial-time permafrost aggradation it is regionally uncommon during the early glacials, especially on the plateau, but frequent during the Upper Pleniglacials in valleys. These features mostly relate to various frost mounds created by injection and segregated ices. The role of ice wedges is really very limited in this zone of southern extent of the European palaeo-permafrost on plateau and terraces. Thermokarst events are mostly susceptible to occur during the coldest part of the glacial. With a more progressive warming or a retrogressive thermokarst triggered by erosion, as in Arctic today, deformations are more gradual, in direct relation with the rheological properties of the sediments and usually local drainage. They are in concurrence with the vegetation dynamic that will limit its expression. Thermokarst events are in first order orbitally forced under control of a maximum insolation and a minimum in precession, as well as during the Weichselian and the Saalian. They are moreover, associated with abrupt warming transmitted by Dansgaerd Oeschger events. Snowiness and mild winter temperatures are probably the main triggers for thermokarst activity as of today. Other events can be triggered by solar activity as at 20 ka or perhaps enhanced by major ash splay as during the MIS 6b Zeiffen interstadial. Thermokarst events are usually followed on the continent by a reorganization of the rivers from braided to meandering systems. © 2018 Elsevier B.V.