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Over 360 people have died and more than 200 have been injured so far due to the catastrophic landslides in Wayanad, Kerala. Rescue operations are continuing, and bodies are still being found.
Such deadly landslides are being reported from the Himalayas to the Deccan Plateau. What are landslides and what are their causes?
Down To Earth (DTE) spoke to experts to find out.
Vikram Gupta, currently with Sikkim University and till recently with the Wadia Institute of Himalayan Geology, is a landslide expert. He said landslides are a very natural process.
When any mountain develops, it moves. If any state of matter is at high energy, it tries to come to low energy, resulting in landslides.
“Till now, our slopes were almost stable. But in the last 10 years, extreme weather events have been happening more frequently. Because of this, the slopes are moving to regain their stability. Be it the Himalayas or any other region, they are behaving the same way,” said Gupta.
JC Kuniyal, chairman of the Centre for Environmental Assessment and Climate Change at the GB Pant Institute located in Almora, Uttarakhand, told DTE, “When a landmass slides from top to bottom due to a steep slope, it is called a ‘landslip’. It is a micro movement. But when it occurs on a larger scale, it is called a landslide. If at least 10 square metres of land is affected, it is termed a ‘landslide’.
He explained, “When water falls with great intensity over an area with loose soil and less vegetation on it and less solid rock below, it begins to flow instead of seeping into the ground.”
In such a situation, a force is created and the land slides from upslope to downslope. This takes the form of a landslide.
Gupta said there are two major triggers for landslides — earthquakes and rain.
“Geology and soil types are constant. What has transformed is climate change and human intervention. This is why landslides are happening everywhere, be it Uttarakhand, Himachal Pradesh, Sikkim or Kerala. Extreme rainfall is not the only cause of landslides in all these places. Schemes like Char Dham and other infrastructure projects are also creating disasters. If we talk about Kerala, extreme rainfall is the main reason there. At the same time, earthquakes are also a cause of landslides in the Himalayan region. But in the past few years, the main reason has been extreme rainfall,” said Gupta.
Kuniyal said high altitude is the most important factor in the occurrence of landslides, be it the Himalayan region or southern India. For example, even in Wayanad, tourism, human activities and construction in areas with a height of at least 2,000 metres have become factors for increasing landslides. Apart from this, extreme weather events are also playing a big role.
The soil in the Himalayan region is made up of sedimentary rock and is loose. The soil of the Deccan Plateau is made of lava and magma, which is also loose.
However, the parent rock of the Deccan Plateau is much more solid compared to the Himalayas. If there is height and lack of vegetation and the soil is loose, it creates a scenario for landslides at both places.
According to Gupta, the behaviour of every landslide is completely different. This is because every slope is different in nature.
The challenge in forecasting landslides is that while we can detect them in time, they can be site-specific. A landslide early warning system will thus give us information only about the location where it is installed.
“Early warning systems can be installed in places with settlements and an existing risk of landslides. But the problem is that it requires political will and a lot of money. Not all landslides can be identified by installing an early warning system,” said Gupta.
Some early warning systems are sensor-based, which estimate the speed of landslides daily and their accuracy is quite good. But the early warning systems installed in India to identify landslides are almost exclusively based on rainfall. Such systems cannot predict the slope on which the landslide will occur.
Many organisations have installed sensor-based early warning systems in India. But the sites where they are installed are known landslide-prone areas. A wiser thing to do would be to install sensor-based early warning systems at places where risk exists, but landslides have not taken place.