The Siwalik Group in the present text are described into three namely

1. Lower Siwalik consisting of sub-greywacke with fine to medium grained clastics containing calcareous cement disseminated throughout the rockmass and interbedded with well developed clays of maroon and chocolate colours,
2. The Middle Siwaliks are a gradation frc greywacke to arkose interbedded with thinner clays and calcareous matter occurring as segregation.

The sandstones are less sorted, coarse grained and soft. The sequence generally starts with a lower alteration of sandy clays and sandstones which gradually merge with massive, soft sandstones above and 3) the Upper Siwalik consist of very coarse clastics. They generally start with a pebble horizon at the base and goes upto conglomeratic horizon. In the basal part the beds alternating with conglomerates are soft sandstones, whereas in the upper part they are generally dull red clays with some sandstones.

Tectonic Setting
The investigated area forming a part of the SianDhar Syncline is structurally very complicated and has undergone repeated phases of tectonic movements during which the litho-units have suffered foldmg fiaultmg and thrustmg. The main structural features which are encountered in the area are:

• Main Boundary Thrust :
  In the investigated area this has brought the rocks of Lower Tertiaries which are now justaposed with the Siwaliks. At number of places this thrust has been displaced by younger transverse faults roughly trending in a NE-SW direction. In the field it was observed that the areas nearby this thrust are showing intense crushing and slickensides. Sometimes the faulted breccia are also found along this thrust.
  
  
• Krol Thrust :
  This has brought the rocks of Basantpur Formation over the Subathus. Drag folds and puckers are intensely developed in the calcareous and shaley horizon of Basantpur Formation. The middle limbs of the puckers are frequently sheared locally producing a coarse strain slip cleavage and the rocks often show effects of cataclasis. Though the beds on the opposite sides of this junction are generally parallel, truncation of strips of Subathu against the trace of this junction near Sataun (not in the model area) is quite remarkable.
  
  
• Giri Thrust :
  It is named after the Giri River (Pilgrim and West, 1928) and separated the Simla Group from the Krol Formation. In the present area the Giri river follows the Giri Thrust except near Dadahu village where this river changes its course due to a transverse fault. Intense crushing, mylonitization and the course of the Giri river are the main criteria for recognizing this thrust in the field.
  
  
• Transverse Faults:
  A number of transverse faults oblique or sometimes perpendicular to the thrust trending NE-SW has displaced mainly Krol Thrust and Main Boundary Thrust at several places.
  
  

Most of the streams, south of Giri river, are following these transverse faults. One of the most important fault winch has changed the course of the Giri river is passing through Dadahu village and named as Dadahu Fault. In addition to these major faults, a number of E-W trending faults parallel to the axes of major synclines have also affected the formations. This E-W trending fault system is more or less contemporaneous with the folding and must have preceded the overthrusting by the pre-Siwaliks Whereas, the faults which are trending NE-SW direction are of recent age. According to our opinion the major landslides are occurring due to these faults as quite good number of landslides are coming in the vicinity of these faults (eg. Jagar ka Khala).

Landslide Hazard Zonation
A natural hazard means the probability of occurrence within a specified period of time and within a given area of a potentially damaging phenomenon. Though hazard is a process and it is very difficult to map a process which has not yet occurred. However, hazard mapping may be defined as "the identification of those sites where there is a likelihood of hazardous events rather than hazard affected sites".

Hazard mapping is stated to be undertaken with respect to 4 key properties, magnitude, location, frequency and time. Under the present study the main emphasis is given on the location of landslides (Spatial).

Terrain Factors
Landslide Hazard Zonation may be defined as a technique of classifying an area into zones of relative degrees of potential hazards by ranking of various causative factors operative in a given area, based on their influence in initiation of landslides. It is therefore, the first task to identify various terrain factors which govern the stability of slope. Under the present study an attempt has been made to prepare a landslide hazard zonation map based on the synthesization of data acquired from various geo-environmental thematic maps.

From the exhaustive literature survey and the field checks, following geo-environmental factors are found which are playing a significant role in causing slope instability problems 'in the area

1. Slope Aspect
2. Slope Morphometry
3. Landuse/Landcover
4. Dip Slope Relation
5. Rockmass Strength
6. Drainage
7. Geology
8. Ridge/Crest Line
9. Road
10. Tectonic/Lineament
11. Relative Relief

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