FISSURE FLOW AS TRIGGERING MECHANISM FOR SHALLOW LANDSLIDES IN THE ALCOY REGION (SE SPAIN)

L.P.H. van Beek, Th.W.J. van Asch & J.T. Buma (Department of Physical Geography, Utrecht University, P.O. Box 80.115, 3508 TC Utrecht, The Netherlands)

In the marly deposits of the Alcoy region detoriation by shallow landslides is the prevailing erosional process. Given the quick response to rainfall periods, which is not consistent with the impermeable matrix of the regolith, preferential flow through fissures might explain the initiation and reactivation of these landslides. Thus water can infiltrate directly at a critical depth where triggering will be related to a decrease in resistance, both as a loss in shear strength and as a loss of total normal stress, due to the wetting of the material. To evaluate the validity of this presumed triggering mechanism a back-analysis for dated landslides is compared to the preliminary results of a model describing the redistribution of infiltration in the regolith through fissures.