Thursday, July 31, 2014

Landslide engulfs Malin village

The news is all around about the massive landslide that occurred in Malin village on 30 July, located in northwest part of Pune district, Maharashtra. It was triggered by torrential rains, where around 150 people are still trapped and missing in those slushy debris, and 31 now being reported dead. The rescue work is being hampered by the continuous downpour in that region. I hope rescue workers are able to pull out survivors, as now it is race against time. Really heart moving images from the disaster site on the news channels.   

Village lady lamenting over the loss of her dear ones and the house that has been totally devastated . (Photo source:
Landslide debri that swept over the village burying 40 houses. (Photo source:
Location of the village - Malin from Google Earth.

The landslide hit the village in the night when the locals where asleep. It seems it took hours to raise the alarm when a local bus driver alerted officials on discovering that Malin and the road leading to it were no longer to be seen - (source BBC). From the images and videos online it looks to me that they contain loose soil, weathered basalt rock fragments, vegetative matter (trees,plants, etc), water and air; which have formed a mixture of slurry that moved down slope. That gives little or no time to escape, indicating that the speed of the slide would have been really fast. Such kind of debris flows are common after a sustained period of intense rainfall, which is supported by the Met department data of 152 mm rainfall that occurred in the past 48 hrs. Apart from the intensity of rain - inherent nature of the slope forming weak or low strength rock/soil, highly weathered rock material and presence of some rock structures (joints and fractures), slope parallel cracks, interface between rock and overlying weathered rock/soil, etc. are one of the reasons for the slope failure uphill. The landslide can also be attributed to different reasons like the role of development (like ground leveling, road construction) and deforestation up-slope, excessive grazing and annual wild fires that make the slope more prone to landslide during heavy rains.

Cattle tracks along slopes while grazing also destabilize the slope during monsoons. (Photo credit: R. Thomas)

Areas that are especially close to the edge of the Western Ghats escarpment are more vulnerable to landslides. Though landslide occurrence is very common during the monsoon along the western ghats of Maharashtra, this occurrence surely highlights the unpreparedness or plans that are required especially for vulnerable communities located along the slopes. Areas prone to landslide occurring along roads that snake through the western ghats are in many places secured by retro-fitting with rock-bolts and geonets. But, what about those villages that are nestled in the valleys of the western ghat escarpments??

A blog article on AGU by Dr. Dave Petley, highlights the use of NASA TRMM landslide warning tool in forecasting potential areas of landslide. The tool - Tropical Rainfall Measuring Mission provides an accurate estimates of the rainfall over the strong-monsoon areas. This information is fed into atmospheric and oceanic models to help in delineating likely places for landslides. In the article, he also points out a geomorphic feature - 'topographic hollow' above the village as a likely feature for concentrating intense rainfall during overland and soil flow, resulting in increase pore water pressure in the soil and later breaking as a debris flow that engulfed the village. 

TRMM data for the Malin landslide, accessed 31st July, the orange colour indicating likely places for landslide.

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