Differences in the occurrence of debris flows in tropical and temperate environments: field observations and geomorphologic characteristics in Serra do Mar (Brazil) and British Columbia (Canada)

Abstract

Debris flows are among the most destructive types of mass movements throughout the world and are not restricted to certain climate zones or geological environments. In opposite corners of the American continent, Canada and Brazil have experienced several historic debris flows. As part of a one-year international exchange program, the lead author compared morphological evidence related to debris flows and the morphometry of watersheds at sites in Canada and Brazil, with the ultimate goal of improving the understanding of debris flows in Brazil. Field surveys carried out in both areas in 2019 and 2020 permitted observation of the debris-flow signatures, as well as the physical aspects of the surrounding areas and morphometric mapping of watersheds. Both areas exhibit similar typical features of debris flows, and the morphometric results indicate differences that may influence the recurrence of events at the sites in Canada as compared to Brazil due to their higher values for the parameters area > 25° (A25), relief ratio (Rr), and Melton ratio (Mr) at the Canadian sites; however, this dataset is limited. Compared to results in the literature from around the world, values of morphometric parameters at Brazilian sites are within the ranges observed in other tropical climates.