Magnitude-frequency relationship for debris flows on the fan of the calance torrent, valgaudemar (french Alps)

摘要

In 1996 a large debris flow occurred on the fan of the Chalance torrent system, a tributary of the Severaisse river. French Alps. To investigate the magnitude and frequency of such debris flows on this fan, fieldwork was carried out in the summer of 1998. Detailed investigation revealed that several debris flows have occurred in the past 200 years. Lichenometry was used as a dating technique to obtain the frequency of these debris-flow events. Also the volume of these flows was estimated. With these data a magnitude-frequency relationship was constructed. This relationship shows a maximum magnitude of at least 50* 10~3 m~3. Based on data for the past c. 150 years, a debris flow of such a volume appears to have recurrence interval of approximately 34 years.