Timing of the last deglaciation revealed by receding glaciers at the Alpine-scale: impact on mountain geomorphology

New Terrestrial Cosmogenic Nuclides (TCN) 10Be ages obtained on glacially polished rocks from the SW Alps (Tinée Valley, France) allow a comparison with ages obtained using similar methods for dating the deglaciation steps after the Last Glacial Maximum on the northern and southern sides of the Alps. The data presented in this study highlight three stages of glacial retreat on the southern flank of the Alps at remarkably similar ages that are 14.9 ± 0.8 10Be ka for the end of Oldest Dryas cold period, 10.9 ± 1.1 10Be ka for the end of Younger Dryas cold period and 8.4 ± 0.9 10Be ka for a late ice retreat stage. Previously published data from the Northern Alps lead also to an age of 15.7 ± 1.0 ka for the Oldest Dryas deglaciation, followed by the Younger Dryas at 11.3 ± 1.0 ka, and a late discrete ice retreat event at 9.7 ± 1.2 ka. The last glacial retreats occur thus simultaneously across the Alps and the deglaciation process was most likely unrelated to variations in latitude or to mountain flank exposition throughout the Alps. This may be ascribed to a relatively rapid climate change. Subsequent mountain slope evolution following the rapid glacier unloading is reflected by landslides and fault reactivation directly following the deglacial period. This temporal coincidence is ascribed to a cause-to-consequence effect of glacial unloading and water infiltration into tectonic and landslide triggering.

► New10Be datings are obtained on glacial polished surfaces in the Southern Alps. ► Three stages of glacier retreats are dated: 14.9 ± 0.8 ka, 10.9 ± 1.1 ka and 8.4 ± 0.9 ka. ► A review of alpine glacier retreat since 20 ka is performed. ► The last glacial retreats occurred simultaneously across the Alps. ► The rapid glacier unloading involves landslides or fault reactivation.