Islahiye catchment, covering an area of 37.7 km P2 in the eastern Black Sea region, was heavily
suffered from earthflows triggered by heavy rainfall in 1995 and 2002 (on July 23). Earthflows caused
17 causalities, four houses were demolished and some engineering lifeline structures were damaged
in the catchment. Total 121 earthflows were recorded in the area. The weathering of the rock units,
existence of steep slopes and human interaction can be evaluated as the main factors conditioning of
earthflows. The main triggering factor of earthflows in the region is rainfall either intensive or long
lasting. The majority of the earthflows were occurred in the weathered zones, which is mainly
composed of inorganic and organic silts and silty clays of low plasticity. The slopes having more than
30 degrees constitute approximately 50 % of the entire catchment which varies between 1.5 and 4.0
km in width and 13 km in length. The minimum and maximum elevation values are 150 m and 1970 m,
respectively. In order to identify other potential earthflow prone areas in the catchment, earthflow
susceptibility assessments were performed using logistic regression analyses. The available raster
data such as slope, aspect, curvature and elevation data were produced from digital elevation model
(DEM) in GIS environment and were employed during the analyses. Two different mapping units
namely pixel and unique condition units were used for performing logistic regression analyses. In
addition, a comparison of performance of the earthflow susceptibility maps of Islahiye catchment was
carried out. It can be said that the susceptibility map prepared based on unique condition units exhibits
slightly better performance than that of pixel unit