A unique boulder-bed reach of the amblève river, ardenne, at fonds de quarreux: Modes of boulder transport

Abstract

The Amblève valley at Fonds de Quarreux displays one of the most spectacular incised landscapes of the Ardenne massif. Cut into highly resistant Cambrian quartzites and surrounded by steep wooded hillslopes, a 3-km-long gorge is cluttered with hundreds of huge quartzite boulders up to several metres in size. These boulders originate from the locally outcropping Cambrian Venne Formation and reached the riverbed through periglacial slope processes. Up to 2-m-large boulders have been transported by the river over distances of several kilometres, some of them being observed 90 km downstream in the Meuse terraces of the Campine Plateau. We show that such transport of very large boulders over long distances cannot occur through purely fluvial processes and conclude that ice rafting was the most likely transportation mode, active during Pleistocene cold periods and probably supplemented by other ice breakup-related processes. We also briefly present nearby sites of geomorphological value within the Amblève catchment.