A methodological approach for the analysis of the temporal occurrence and triggering factors of landslides

The temporal occurrence of landslides in an area of the Cantabrian Range during the last 120,000 years is analyzed. An initial relative chronology was established on the basis of aging degree and spatial relationships between landslides and glacial and fluvial features. Ten landslide classes were thus identified and their chronological limits defined on the basis of 19 C-14 age determinations on fluvial and glacial deposits (including eight new ones). The chronology was tested with C-14 dates obtained on landslide deposits, 10 from previous work and nine new ones. The chronological classes identified were compared with existing climate models for the region; the type and spatial distribution of landslides in each class were also analyzed. The approach made it possible to identify periods during which landslides were triggered mainly by channel incision, seismic activity and rainfall increase. Human activity played a significant role after 5000 BP and especially in the last few centuries. Mobilization of materials by slope movements has increased in the region by a factor of 10, compared to pre-Neolithic rates. (C) 1999 Elsevier Science B.V. All rights reserved.