Deforestation, poorly planned infra work affecting Himalayas, says Petley
Petley said that while heavy rain and tectonic activity may trigger such events, human activity can also trigger instability
The crisis in Joshimath is an instance of gradual landslide that might have been accelerated due to human activities, scientists and geologists have said. University of Hull vice-chancellor, Professor Dave Petley in an email interviewsaid that while heavy rain and tectonic activity may trigger such events, human activity can also trigger instability, especially where the slope is undercut for road building, poorly designed hydropower projects, deforestation or where water is not being managed well. Edited excerpts:
Q. What is your impression of Joshimath event? Earlier, experts had termed it a subsidence event.
A. The event at Joshimath is being caused by the movement of an ancient landslide upon which the town is built. The landslide is moving down the slope, causing damage to the buildings. I think calling this a subsidence event is misleading, as this implies that there is vertical motion, whereas in reality the movement is downslope.
Q. What is the difference between subsidence and landslide?
A. Strictly speaking, subsidence is vertical movement, whereas a landslide will move downslope. Landslides usually involve both horizontal and vertical motions, as is the case here.
Q. What causes such landslides? What role do mega projects such as highways, roads, rail, hydropower play in such events?
A. Landslides are a natural process in high mountains, and indeed Joshimath is built on an existing ancient landslide complex. These slopes will occasionally move as a result of, for example, unusually heavy rain or a large earthquake. But human action can also trigger instability, especially where the slope is undercut for road building, for example, or where water is not being managed well. It is impossible to pinpoint the exact cause of this round of movement of the landslide without a proper investigation. In general, across the Himalayas, we are seeing landslides being triggered by human activity, including road building, urbanisation, deforestation and poorly designed hydroelectric schemes.
Q. Several parts of Himalayas are facing similar events. How can they be prevented?
A. We can reduce the likelihood of these events by ensuring that we minimise the disruption to the natural equilibrium... we preserve forests. We should ensure that we properly engineer large infrastructure projects (such as roads, railways, tunnels and dams), set them up in appropriate locations and that we maintain good drainage.
Q. Why are the Himalayas so vulnerable to landslides? What kind of development is recommended in the Himalayas?
A. The Himalayas are a geologically-young mountain chain. The mountains are being pushed up rapidly by the collision of the Indian and Eurasian tectonic plates. At the greatest scale, this is creating an unstable landscape which undergoes landslides to try to restore the balance. The area also suffers occasional large earthquakes, which cause instability. On top of that, the monsoon climate means that at times there are very high inputs of rain, which triggers landslides. Finally, the environment of the Himalayas is being degraded at a high rate – the clearing of forests, the construction of poorly engineered roads, the blocking of rivers through dam construction are all significantly impacting it. Of course, rain patterns are changing as a result of climate change. It is possible to mitigate the impact of landslides through proper land use planning, management of water and well-designed engineering. However, often development is not well planned, and the quality of engineering is low.
Q. How much area of Joshimath town may be impacted as per your reading of satellite data?
A. That is impossible to say without more detailed mapping and monitoring.
Q. Does the entire town need to be rehabilitated?
A. Again, I simply do not know based on the evidence available. According to reports, there are detailed investigations underway by a range of groups, which needs to be the basis for this type of decision.