Differentiate the Causes of Landslides in the Himalayan region and Western Ghats

Landslide refers to the sudden movement of rock mass, debris, soil, or vegetation down the slope due to the force of gravity. It is a type of mass wasting, which denotes any downward movement of soil and rock, and areas with steep slopes are more susceptible to landslides. Mass movement, Earth flow, mud flow, debris flow, rotational slides, avalanches are some of the examples of landslides. Landslide is one of the major hydro-geological hazards which affect a large portion of India. According to the Geological Survey of India (GSI), 12.6 per cent of the total country’s land area (around 0.42 million square kilometres) is prone to landslides. The Himalayas of Northwest and Northeast India and the Western Ghats of Peninsular India are the most vulnerable regions to landslides.

Landslide may be caused by natural factors such as heavy rain, snowfall, earthquake, or it may be induced by human factors like over-interference with the slope-stability by deforestation, unplanned construction, or mining. The intensity and magnitude of the landslide largely depend on the geological structure, slope angle, nature of rocks, and human interaction. It is observed that the causes of landslides in the Himalayan region and the Western Ghats are different. Landslides in the Himalayan region are usually due to natural causes such as high seismicity due to plate tectonic movement, easily erodible sedimentary rocks, young and energetic rivers with high erodible, heavy downpour, and snowfall whereas landslides in the Western Ghats are mainly due to concentrated rainfall, overburdening of hills, mining, and quarrying.  

Landslide Prone Regions in India:

 A. Himalayan region

• The Western Himalayas (Jammu & Kashmir, Uttaranchal, Himachal Pradesh, and Uttar Pradesh)
• The Eastern & North-eastern Himalayas (Arunachal Pradesh, Sikkim, and West Bengal)
• The Naga-Arakan Mountain belt (Nagaland, Manipur, Mizoram and Tripura).

B. Peninsular India

• The Western Ghats region (Maharashtra, Goa, Karnataka, Kerala & Tamil Nadu).
• The Plateau margins of Peninsular India and Meghalaya plateau in North-East India.

Differentiate the Causes of Landslides in the Himalayan Region and the Western Ghats:

A. The Difference in Natural Causes:

1. Plate Tectonic movement: Indian Plate is moving towards the Eurasian Plate and collides with it. The Himalayan region lies in the north of the Indian Plate and due to collision with Eurasian Plate, it is tectonically active which causes frequent tremors. This isostatic imbalance causes frequent landslides. Whereas the Western Ghats region is tectonically more stable and has less frequency of tremors and landslides due to it. Therefore the causes of landslides in the Western Ghats are different from the Himalayan region in terms of geotectonic.
2. Rock structure: The  Himalayan region is comprised of sedimentary rocks. These rocks are more susceptible to denudation and erosion as compared to the rocks of Western Ghats. With little rainfall and construction activities, sedimentary rocks result in denudation whereas the major part of Western Ghats is comprised of basalt rocks. These rocks have great resistance to erosion and denudation and result in fewer landslides due to differences in rock composition.
3. Earthquakes: Earthquakes are the most important factor for the landslides in folded mountain regions. Due to this, landslides appear more frequently in the folded mountains of the Himalayas. In 1905, an earthquake in the Kashmir valley resulted in a severe landslide that took the lives of several thousand people. But the Western Ghats are less susceptible to Earthquakes and have fewer Earthquake-induced Landslides.
4. Topography and Exogenetic Forces: Many young and rapid-flowing rivers such as the Ganges, the Indus, and the Brahmaputra originated in the Himalayan region. These rapid-flowing rivers cause large-scale denudation and erosion of mountainous regions. The Himalayas are mighty, having steep slopes and easily eroded by rivers due to their topography, which leads to landslides. Whereas the Western Ghats have mature rivers and denuded topography which rarely yields further denudation and erosion and as of this, it results in fewer landslides.
5. Rainfall and Snowfall: Heavy or continuous downpours may result in severe landslides particularly in the regions of steep slopes due to denudation and soil erosion. Both the Himalayan region and the Western Ghats face severe landslides due to concentrated rainfall.

B. The Difference in Anthropogenic Causes: 

1. Human Interference: Developmental activities such as infrastructure activities in form of roadways and railways, unplanned and haphazard urbanization particularly ignoring the relief and topographical aspects of the landform, illegal building construction, etc, have aggravated the occurrence of landslides. The Western Ghats is notified as one of the Biodiversity Hotspot zones and due to this the human interference is less as compared to the Himalayan region. But overall both the regions i.e. the Himalayan region and the Western Ghats are facing a number of landslides due to unsustainable development by humans.
2. Deforestation: Deforestation is one of the major factors of human-induced landslides. Deforestation for settlements, road construction, agricultural fields, etc is prominent in both the Himalayan region and the Western Ghats.  Jhum cultivation (Slash and Burn) in northeast Himalaya, illegal tourism infrastructure development in Uttarakhand and Himachal Pradesh, and similarly in the Western Ghats results in deforestation and ultimately in a landslide. Therefore, a change in vegetation cover in both regions results in landslides.
3. Mining and Quarrying: Extraction of coal, iron and other minerals from the mines and quarries of mountains generally create favourable instances for landslides. For example, limestone mining in Himachal Pradesh, quarrying activities in Banasuramala, Kerala for building stone are the areas where mining and quarrying results in landslides as these activities affect the slope stability.
4. Unplanned construction of houses: In the hilly areas, the unplanned growth of towns and cities without testing soil conditions and rocks structure becomes an important cause of landslides. For example, Nainital (Uttarakhand) is facing landslide problems due to the heavy load of hotels, and other residential infrastructure.