• erosion;
  • miniature debris flows;
  • visual observation;
  • black marl;
  • sediment load


In order to clarify the erosion processes on a marly bare slope in the Southern Alps, the erosion processes in a steep and erodible slope composed of the Black Marls Formation were observed by a time-lapse video camera. The observations revealed that miniature debris flows (MDFs) occurred at the time of the rainfall-runoff event in which the most severe erosion took place in the whole observation period of 3 months. Analysis of the camera images showed some characteristics of the MDFs, and these are discussed in the context of real rainfall-runoff phenomena observed at the outlet of a small experimental basin including the visually observed slope. The following results were obtained. (1) A rough estimation of the total amount of sediment discharge by the MDFs showed that it was not negligible quantitatively. (2) The MDFs occurred only during the rising limb of the hydrograph during 6 minutes. (3) Based on this observation and a review of the literature, in a very steep and highly erodible slope, MDFs or similar phenomena might play an important role in the erosion and transport processes. Copyright © 2008 John Wiley and Sons, Ltd.