The Malin landslide last July, which killed more than 100 people, was not just a consequence of manmade interventions, but was also the result of a tectonic phenomenon, a new paper revealed.
Remote sensing satellite data has shown that Malin, situated in Pune district, is a “tectonic block” that is bound by fault lines on all sides. With the likelihood of more landslides in the “tectonically active” region, the paper recommended that geological aspects must also be taken into account in the “anthropogenically invaded” (destruction caused by humans) Malin, while drawing up preventive measures.
The paper ‘Malin-Maharashtra landslides: A disaster triggered by tectonics and anthropogenic phenomenon’ was published in Current Science by the Indian Academy of Sciences, Bangalore.
According to the study, cracks were observed in the region a decade ago — three of which were found in 2003 by locals. “The Indian plate is partially moving northwards, pushing up the Himalayas, to collide with the Eurasian plate. The remaining force is getting adjusted with the Indian plate buckling or moving up and down,” said SM Ramasamy, department of science and technology geospatial chair, centre for remote sensing, Bharatidasan University, Tamil Nadu. “In addition, cracks being formed in the northeast-southwest and northwest-southeast direction have opened up fault lines, which can clearly be seen in Malin through satellite images.
Soon after the Malin tragedy, government authorities, geologists and environmentalists had cited two possible causes for it — deforestation for bench cultivation of paddy in the upslope region of the village and large scale flattening of the foothills in the downstream of the village. In addition to using large quantities of water for crops that loosened the soil leading to major mudflow, heavy rainfall for three days also caused the landslide.
“With fault lines opening up because of tectonic activity, water used for intensive paddy cultivation seeps into these opened fractures, in addition to the effects of deforestation and disturbance in the downslope of the village. These factors contributed to an increase in pore pressure,” said Ramasamy.
“When pore pressure goes beyond the critical point, landslides occur because water detaches the bond between soil particles, thereby altering its strength. The loosened soil has a great impact on the stability of the slope since it slides out,” Ramasamy said.
AK Saha, former director, Geological Survey of India (central region), who visited Malin after the landslide and submitted a report to the Centre, however, refuted the study.
“The landslide had nothing to do with tectonics. This [paper] has been established after the incident; more like a post-mortem,” said Saha. “The landslide was because of slope development and erosion, which does not retain the thick soil profile. In addition, excessive rain also became a lubricant between the hard rock and the loose soil.”
Concluding that the Malin landslide was a combination of tectonic and anthropogenic phenomena, the paper suggested some measures to prevent future occurrences. Some of measures include mapping lineaments, which will show the growth and modification of the faults, detailed structural mapping, GPS-based monitoring of the cracks/fractures, detailed geomorphic mapping, land use and land cover mapping using multi-dated satellite images and detecting changes in land use/land cover vis-à-vis rainfall and landslides.