The effect of terrain factors on landslide features along forest road

The objective of this study was to investigate the effects of physiographic features such as slope, altitude, aspect and soil on landslides dimensions and distribution in Pahnehkola forest, north of Iran. 30 landslides were selected for detailed observation, with their occurrences recorded by global positioning system (GPS) along the surveyed forest road. Then, landslides were mapped in Arc view and subsequently digitized into a geographic information system (GIS). Results indicate that the landslide area at a distance of 80 to 100 m from road edge was significantly more than that of other distances. The landslide dimensions increased with increasing slope angle. The mean of landslide area and mean of landslide volume on the Northwest aspect was significantly more than that on other aspects (P<0.01). The mean of landslide dimensions in altitude class of 400 to 650 m was significantly less than that in altitude class of 150 to 400 m (P<0.01). The mean of landslide dimensions increased significantly with increasing soil liquid and plastic limit. The logistic regression modeling indicate that independent variables including aspect, liquid limit, plastic limit and soil moisture, significantly influence the landslides area. The majority of landslides were situated along roads and on faults, and shallow landslides were more frequent along roads compared to those on faults.Key words: Landslide, forest road, physiographic features, GPS, Pahnehkola forest