Dendrogeomorphological analyses of trees affected by debris flows have regularly been used to date past
events. However, while previous studies in the Swiss Alps have focused primarily on granitic and gneissic debris-flow
material and on Larix decidua Mill. and Picea abies (L.) Karst. trees, they have – at the same time – widely disregarded
torrents dominated by finely fractured calcareous and dolomitic lithologies and forests populated with Pinus sylvestris L.
In this paper, we report on results obtained from a debris-flow cone in the Rhone valley (Valais, Switzerland) where very
fine and muddy material (limestone, dolomite, quartzite and calcite) occasionally affects P. sylvestris trees. Based on the
results of a geomorphic map, 1004 increment cores from 451 disturbed P. sylvestris, 37 L. decidua and five P. abies trees
were sampled, allowing reconstruction of 15 events between AD 1793 and 2005 as well as the determination of breakout
locations of events. From the data, it also appears that debris-flow material only rarely left the incised channel over the
last 200 years and that overbank sedimentation events did not occur after 1961, when a rockslide delivered large amounts
of erodible material and subsequent debris flows caused an important incision of the canyon on the cone.