Most of the models for landslide susceptibility zonation (LSZ) except machine learning needs manual selection of weights or ratings, which are given by expertise knowledge, leading to subjectivity and specificity. Hence, selection of ratings is very important in the preparation of LSZ maps. Here, seven layers/factors viz. aspect, elevation, geology, slope, soil, distance from stream, distance from thrusts are considered for LSZ mapping in Mandakini River basin, Uttarakhand containing 1,805,636 pixels. The weights were calculated using information value (InfoVal) method. The occurrences of landslides (2009 pixels) until 2008 were considered for training of model. Thus for giving rating to each thematic layer, 7! = 5040 permutations (ratings) are possible. Hence, 5040 LSZ maps were prepared and out of them, the best rating was identified using fisher discriminant analysis (FDA) and binary logistic regression (LR). FDA and LR gave similar ratings and the correlation (r²) between their weights was 0.9226. Thematic layers were then multiplied by the corresponding ratings and added to prepare the final LSZ map. The results were validated on the landslide data until 2011, which were not used for training. Out of 223 occurrences of landslides, 39% (87) falls in high susceptible zone followed by 35% (79) in very high susceptible zone according to FDA and similar for LR. The accuracy of the prediction was assessed by Heidke-Skill-Score, which gave score of 0.89 to FDA and 0.90 to LR for 0.5 as threshold of landslide susceptibility index.

Landslide is a global natural hazard that occurs frequently in the areas of incompetent weak rocks, undulating topography, steep slopes and incessant rainfall. In the night of 12 August 2017, a massive landslide took place at Kotrupi, Mandi district, Himachal Pradesh, India. The slide was so huge that it eroded more than 300-meter stretch of NH-154 killing over 50 people with more than 40 missing. Local residents report that this area has always been unstable where small landslides had occurred in the past. The landslide scar could be seen on the past satellite images from December 2001 to March 2017 on Google Earth. A huge landslide occurred at this location on 13 August 1977. After two decades on 13 August 1997, the landslide reactivated and some part of the slope failed, which can be seen on satellite images of the year 2001. The landslide reactivated again on 13 August 2007, but not much attention was given to it, as it was a small event and did not affect much. Again, after a decade, in the night of 12 August 2017 this landslide was reactivated. There is the possibility of reoccurrence of slope instability from upper reaches of the crown area of the main slide complex as well as the debris, which have been already accumulated on hill and valley side. Based on the geological, geotechnical and geophysical investigations the site stability can be done but its monitoring from satellite provides the information for its future preventive measures.