Holocene, vol.19, no.6, pp.955-965, 2009 (SCI-Expanded)
Mass instability in the uplifting footwall blocks of normal faults involves a range of regional and local factors including, among others, climatic setting, topography, lithology and particularly ground shaking during earthquakes. Morphological and sedimentological investigations backed by 14C dating on a huge debris flow and its zone of depreciation provided favorable insights for dynamics and causative factors of this mass wasting. Our observations showed that İsmetpaşa Debris Flow with a volume of 96 km3 involves three individual flows of decreasing significance in the late Pleistocene-Holocene period. The primary flow occurred in relation to a huge landslide developed on highly fractured and altered basaltic lavas near the crest of fault scarp c. 18.7 ka BP and probably conditioned by high precipitation rates in the early Interglacial. Although, most of the blocky debris flow transferred into the neighboring graben to form a 2 km wide debris fan, some remnant blocks and flow-induced valley-side slickensides can still be observed in the zone of depreciation. One km long secondary flow was sourced from the remnants of primary flow and was realized at 7.9 ka BP in another humid period of the Holocene. The third, though minor (less than 100 m long), mobilization of the flow occurred on one of the steep faces of secondary flow in 1960s when the mean precipitation was higher than that of today. Good coincidence of timing of individual debris flows with the humid phases of the late Pleistocene-Holocene period showed that long-term antecedent precipitation is the dominant causative factor. © The Author(s), 2009.