Toward the Mechanism of Deadly Landslide and Debris Avalanche in Abikar Village, Farsan City, Chaharmahal and Bakhtiari Province, Iran

 On the evening of April 1, 1998, in Farsan city, Chaharmahal and Bakhtiari Province, western Iran, the southern edge of the valley of Mt. Kino, along the Labad river, slid down into the river valley, where the moved material sloshed up over hill on the opposite river bank to bury Abikar village. This event followed an exceptional rainfall exceeding 190 mm during a week. In this research, the unexpected behavior of the landslide, the possible causes of the long-runout of debris, and the probable mechanism of such movement are discussed.

 This disaster was investigated, we attempted to offer a schematic model for its occurrence using various field data such as structural geology, surface soil layers, local geomorphology, meteorological data, hydrology, and field evidence. The disaster claimed the life of 54 people, and 1300 livestock, and the destruction of 40 hectares of farmlands and orchids.

 The remain of the disaster contains some extraordinary features such as the lack of debris or barrier across the river, high debris flow velocity, the transformation of some debris material by jumping into the far end of debris flow, and a severe air storm in front of the debris flow mass.

 We suggest that, when a giant slab of rocks fell down from the opposite flank, the generation of debris avalanche and the formation of an air cushion underneath the debris could be one of the reasons that facilitate the long runout of detrital flows.