Context:

The Council of Scientific And Industrial Research -National Geophysical Research Institute (CSIR-NGRI) has launched an ‘Environmental Seismology’ group to develop a ‘Landslide and Flood Early Warning System’ for the Himalayan region.

Relevance:

GS-III: Disaster and Management (Natural and Anthropogenic Disasters, Disaster Management in India), GS-I: Geography (Important Geophysical phenomena), GS-III: Science and Technology

Dimensions of the Article:

  1. What are Landslides?
  2. 2 Primary varieties of Landslides in India
  3. Why are Landslides more frequent in the Himalayas than in the Western Ghats?
  4. Geographical distribution of floods in India
  5. About Increased Flood risks in Bihar and Nepal (Himalayan) region
  6. NGRI’s Landslide and Flood Early Warning System

What are Landslides?

Landslides are physical mass movement of soil, rocks and debris down the mountain slope because of heavy rainfall, earthquake, gravity and other factors.

Why do Landslides Occur?

  • Base of the huge mountains eroded by rivers or due to mining activities or erosion agents resulting in steep slopes.
  • Increased industrialisation leading to climate change and weather disturbances.
  • Change in river flow due to construction of dams, barriers, etc.
  • Loose soil cover and sloping terrain.

2 Primary varieties of Landslides in India

I- Himalayas

  • India has the highest mountain chain on earth, the Himalayas, which are formed due to collision of Indian and Eurasian plate, the northward movement of the Indian plate towards China causes continuous stress on the rocks rendering them friable, weak and prone to landslides and earthquakes.
  • The Northeastern region is badly affected by landslide problems causing recurring economic losses worth billions of rupees.

II- Western Ghats

  • A different variety of landslides, characterized by a lateritic cap (Laterite is a soil and rock type rich in iron and aluminium , and is commonly considered to have formed in hot and wet tropical areas), pose constant threat to the Western Ghats in the South, along the steep slopes overlooking the Konkan coast besides Nilgiris, which is highly landslide prone.

The problem needs to be tackled for mitigation and management for which hazard zones have to be identified and specific slides to be stabilized and managed in addition to monitoring and early warning systems to be placed at selected sites.

Zone Map

Himalayas of Northwest and Northeast India and the Western Ghats are two regions of high vulnerability and are landslide prone.

Why are Landslides more frequent in the Himalayas than in the Western Ghats?

In the Himalayas, Landslides are very frequent because:

  1. Heavy snowfall in winter and melting in summer induces debris flow, which is carried in large quantity by numerous streams and rivers – which results in increases chances of Landslides.
  2. Himalayas are made of sedimentary rocks which can easily be eroded – hence, erosions contribute to more landslides.
  3. Drifting of Indian plate causes frequent earthquakes and resultant instability in the region.
  4. Man-made activities like grazing, construction and cultivation abet soil erosion and risks of landslides.
  5. Himalayas not yet reached its isostatic equilibrium which destabilizes the slopes causing landslides.
  6. Diurnal changes of temperature are much more in northern India than in southern slopes – weakening the rocks and increasing mass wasting and erosion.

In the Wester Ghats, Landslides are comparatively less frequent because:

  • Western Ghats are eroded, denuded, aged, mature, worn out by exogenic forces and have a much lower height – hence, occurrence of Landslides is lesser.
  • The Western Ghats are on more stable part of Indian plate, hence, there is a lesser occurrence of earthquakes and landslides.
  • While steep slope on western side with high rainfall creates idea condition for landslide but gentle eastern slope with low rainfall and rivers in senile stage, counters the condition.
  • Moving of Indian plates doesn’t affect the Western Ghats much (as they are old block mountains), hence the reduced number of landslides.
  • Small & swift flowing streams of western side and big matured rivers on eastern side (like Krishna, Godavari, etc) cannot carry large amount of debris.

Geographical distribution of floods in India

  • Rashtriya Barh Ayog (National Flood Commission) identified 40 million hectares of land as flood-prone in India.
  • Historically, Bihar has been known to be India’s most flood-prone State. The Flood Management Improvement Support Centre (FMISC), Department of Water Resources, Government of Bihar estimates that 76% of the population in north Bihar faces the recurring threat of flood devastation.
  • Assam, West Bengal and Bihar are among the high flood-prone states of India.
  • Most of the rivers in the northern states like Punjab and Uttar Pradesh, are also vulnerable to occasional floods.
  • States like Rajasthan, Gujarat, Haryana and Punjab are also getting inundated in recent decades due to flash floods. This is partly because of the pattern of the monsoon and partly because of blocking of most of the streams and river channels by human activities.
  • Sometimes, Tamil Nadu experiences flooding during November – January due to the retreating monsoon.

About Increased Flood risks in Bihar and Nepal (Himalayan) region

  • A large part of north Bihar, adjoining Nepal, is drained by a number of rivers that have their catchments in the steep and geologically nascent Himalayas.
  • Originating in Nepal, the high discharge and sediment load in the Kosi, Gandak, Burhi Gandak, Bagmati, Kamla Balan, Mahananda and Adhwara Group wreak havoc in the plains of Nepal’s Tarai and Bihar. About 65% of the catchment area of these rivers falls in Nepal/Tibet and only 35% of the catchment area lies in Bihar.
  • A study indicated that the plains of North Bihar have recorded the highest number of floods during the last 30-years. In the years 1978, 1987, 1998, 2004 and 2007, Bihar witnessed high magnitudes of flood.
  • Flood of 2004 demonstrates the severity of the flood problem when a vast area of almost 24 thousand Sq Km was badly affected by the floods of Bagmati, Kamla & Adhwara groups of rivers causing loss of about 800 human lives, even when Ganga, the master drain was flowing low.

NGRI’s Landslide and Flood Early Warning System

  • CSIR-National Geophysical Research Institute (NGRI) has launched an ‘Environmental Seismology’ group to develop a ‘Landslide and Flood Early Warning System’ for the Himalayan region based on real-time monitoring with dense seismological networks, coupled with satellite data, numerical modelling and geomorphic analysis.
  • This warning system would enable a crucial warning several hours prior, which will save precious human lives and property in future during such events.
  • The need for such an early warning system was necessitated following February 2021’s rockslide flood disaster in Chamoli (Uttarakhand), where a steep glacier on the Nandadevi peak in Garhwal Himalaya got detached, causing a major avalanche and inducing flash floods in the Rishi Ganga and Alaknanda rivers.
  • Teleseismic signals from the beginning of this event were recorded at different stations on a regional seismic network up to 100 km from the disaster and demonstrated the potential for these far-away monitoring stations to be useful for early warning according to the research study.
  • While a seismic network designed for earthquake detection may not be ideal for the monitoring of geomorphic events, an evaluation of the expected anthropogenic (man-made) and environmental noise levels should be carried out before locating stations for geomorphic event detection.

-Source: The Hindu

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