12 per cent of India's land mass vulnerable to landslide: GSI

Over 12 per cent of the country's total land area, which amounts to around 0.42 million square kilometres, is vulnerable to landslide hazard, the Geological Survey of India has said.

About 12.6 per cent of the total land mass of India falls under the landslide-prone hazardous zone, according to a study by the GSI, under the directive of the Ministry of Mines.

"Out of the total land area prone to landslide, 0.18 million square kilometres fall in the North East Himalayas, including Darjeeling and Sikkim Himalaya. About 0.14 million square kilometres fall in North West Himalayas in states like Uttarakhand, Himachal Pradesh and Jammu and Kashmir," the study said.

"Another 0.09 million square kilometres in Western Ghats and Konkan hills in states like Tamil Nadu, Kerala, Karnataka, Goa and Maharashtra and 0.01 million square kilometre in Eastern Ghats of Aruku area in Andhra Pradesh are found to be landslide-prone," it said.

As per the Ministry of Mines' directive in 2013, the GSI envisaged a six-year-long national programme, the National Landslide Susceptibility Mapping (NLSM), in each of its regions from field season (FS) 2014-15 to prepare seamless 1:50,000 scale landslide susceptibility maps following a GIS-based approach.

According to a senior GSI scientist, the GSI-based approach was done through development and use of site-specific/terrain-specific weights/ratings, adequate field and remote sensing inputs.

"The landslide-prone Himalayan terrain also belongs to the maximum earthquake-prone zones where earthquakes of Modified Mercalli intensity VIII to IX can occur, and thus, are also prone to earthquake-triggered landslides," the geologist at the GSI headquarter here in Kolkata told PTI.

The GSI has the onus as the "nodal agency" for the Indian government for landslide data repository and landslide studies and it is engaged in all types of landslide and slope stability investigations. In fact, GSI has been carrying out macro scale (1:50,000) landslide susceptibility zonation since last four decades.

However, compared to the available landslide-prone areas in India (0.42 square kilometre), the target achieved so far by GSI (60,000 square kilometres) till FS 2013-14 has been only 14 per cent.

Moreover, the existing landslide susceptibility maps are old and analog maps which are difficult to be disseminated and updated in future. This warranted GSI to impart maximum stress on completion of this basic task on landslide susceptibility at a faster pace.

For the NLSM, the GSI is using an internationally peer-reviewed methodology on 1:50,000 scale, exclusively developed through a four-year-long (2007-2011) international research in collaboration with the Faculty of Geo-information Science and Earth Observation (ITC), University of Twente, The Netherlands.

The NLSM project in vogue has been conceived, monitored and mentored continuously by the landslide experts of the newly-constituted Geohazards Research and Management (GHRM) Cell, CHQ, Kolkata.

Talking more about the project, the GSI official said for the completion of the entire NLSM target (0.42 million square kilometre), two priorities are identified — Priority 1 (about 66 per cent of the target) areas where habitation and roads exist is based on both the high-resolution remote sensing (RS) and field inputs.

The other one is the Priority 2 (about 34 per cent of total target) which are high-altitude and extremely inaccessible areas where fieldwork is difficult (or minimal) and the inputs maps are mostly based on high-resolution Remotely Sensed (RS) data.

During FS 2014-15, six per cent of NLSM Target in Priority 1 (16480 square kilometre) was completed by GSI in FS 2014-15 on a priority basis in Uttarakhand as per the advice of the Committee of Secretaries (CoS) led by the Cabinet Secretary of the Central government.

The reports of all the completed items of NLSM in Uttarakhand have already been handed over to the Uttarakhand Government.

It was learnt that during the FS 2015-16, NLSM work is in progress with the deployment of 75 trained geoscientists in all the landslide prone Regions of India (NR, NER, ER, CR and SR) in 36 on-going items.

"We are expecting that 42 per cent of NLSM target in Priority 1 (1,16,150 square kilometre) is expected to be completed by the end of XII th  Five-Year Plan (end of FS 2016-17)," the official said.

And the entire target of Priority 1 is expected to be completed by the end of FS 2019-20, he added stressing that it is estimated that economic loss due to landslides may reach between 1-2 per cent of the gross national product in many developing countries.