
SRINAGAR: Land sinking in the Pernote area of J&K's Ramban district on the Srinagar-Jammu highway had been triggered by the inherent geological condition of the terrain and prolonged rainfall in the region, revealed a study by the Wadia Institute of Himalayan Geology (WIHG) Dehradun in April 2024.
Authorities had to relocate people of the Pernote area to safer places after the land sinking in April last year caused significant damage, destroying houses, power lines, transmission towers, road connectivity and water supply.
A three-member team of scientists from WIHG Dehradun conducted a detailed geological investigation in and around the area after receiving a notice from the National Green Tribunal (NGT) in November 2024.
According to WIHG report, the landslide took place along this transect at Pernote village.
“At the site location of the landslide, slide materials consist mostly of purple mudstones and sheared and fractured clasts of sub-mature to mature sandstones. The landslide affected area measures about 0.60 sq km; 1.25 km in length, 650m width and height of 450m to 500m,” the report read.
“The overburden of the slope is made up of clasts of unconsolidated and heterogeneous rock fragments, which lack cohesion generated by old landslides. The nature of the landslide is debris slide. At Pernote and its adjacent area, it is observed that during heavy rainfall most of the infiltration through these water sensitive lithologies (alternation of mudstones, siltstones, and sandstones) usually oozes out as seepage,” it stated.
“A number of old landslide scars are observed in the slope where the present landslide occurred. Ramban area including Pernote village falls in the UT of Jammu and Kashmir which is located in a seismically active zone (Zone IV-V as per India's seismic zonation). However, no such geological phenomena e.g., seismic activity, have been noticed or reported anywhere till now in the landslide-affected area,” the study further stated.
On what triggered the land sinking, the WIHG study reveals that the inherent geological condition of the terrain material forming the slope is the main factor for the landslide that took place at Pernote village on April 25, 2024.
“The landslide occurred at the footwall blocks of Murree Thrust where the rocks are highly sheared and fractured that are very friable. The slope is made up of alternation of mudstone, siltstone, and sandstone. These intervening layers of mudstone in between the lithologies make the slope prone to landslides. Mudstone is often very soft and breaks up easily,” it said.
The study further revealed that the thick loose overburden forming slope materials is made up of clasts of purple mudstones and sheared and fractured clasts of sub-mature to mature sandstones is of old landslide debris.
“The slope of the region falls in steep to very steep slopes, which is sufficient to bring down the loose, swelled materials downslope during heavy rainfall, initiating the landslide,” reveals the study.
According to the WIHG study, the prolonged rainfall was the triggering factor for the landslide, as the area received continuous rain before the landslide.
“The water-saturated sediments got swelled, and their low permeability reduces the shear strength of the sediments, resulting in the mass of sediment sliding along the steep slope,” it stated.
The WIHG has suggested that the first step for slope stabilization is to get rid of the water by dewatering the affected slope and diverting the water away from the landslide area as water is the main agent for slope instability.
“Barren upper slopes should be afforested - plantations of fast growing root/eucalyptus, alder, willow etc. to arrest the unconsolidated sediments, slope should be benched, use of bioengineering techniques to stabilize the affected slopes, Impermeable materials such as mortar, asphalt, spray, geosynthetic clay liner to act as hydraulic barrier for freshly exposed slopes. Retaining walls with weep holes and earth buttresses for base support. Slope angle >40° should be left undisturbed,” the WIHG further suggested to prevent land sinking.