The Landslide Blog is written by Dave Petley, who is widely recognized as a world leader in the study and management of landslides.
Recovery operations continue at the site of the 30 July 2024 Wayanad landslides in Kerala, SW India. The official loss of life is 231 people as of 17 August, with reports indicating that a further 119 people are believed to have died, leading to an aggregate toll of 350 people.
Planet Labs captured a good quality image of the site on 12 August, with a clear view from the source (indicated by the blue marker on the image) right the way down to Chooramala (which is the point at which the original channels goes through to horseshoe bends just to the east of the larger cloud) and beyond:-
Planet Labs image of the 30 July 2024 landslide at Wayanad in Kerala, India. Image copyright Planet Labs, used with permission, captured on 12 August 2024.
For reference, this is a rough image compare with another Planet Labs image, captured on 6 March 2024:-
Reuters has posted a very good pictorial story that highlights the impact of the landslide on the community using this imagery.
There are a number of interesting aspects to this image. First, it is surprising that there are now other obvious failures on the hillsides around the source of the landslide. Below is a subset of the imagery, showing just the upper portion of the landslide, and the surrounding hills:-
Planet Labs image of the source area of the 30 July 2024 landslide at Wayanad in Kerala, India. Image copyright Planet Labs, used with permission, captured on 12 August 2024.
Usually, large, channelised debris flows have multiple sites of failure around the source area. This suggests to me that the site in which the landslide started must have been particularly susceptible to failure. The source had suffered an earlier, smaller landslide, which occurred in 2020, which also transitioned into a channelised debris flow, but with a shorter runout. The implication is that this smaller event left the source area in a vulnerable condition.
The track of the 30 July event might imply a single, large-scale failure in the source area – note that the channel width remains approximately constant for a considerable distance.
Some reports have indicated that the expert panel has an initial conclusion that there was a “damming effect” that led to the catastrophic debris flow. For what it is worth, I see nothing in the imagery that supports this view, but field work might provide a different perspective.
Another view is that quarrying played a role, but again I do not see anything to support that conclusion (but I do of course recognise that poor mining practise has played a significant role in landslide in other locations).
The impact on the settlements downslope was horrendous. The Planet Labs image of the populated areas of the channel shows very high levels of destruction:-
Planet Labs image of the populated area of the 30 July 2024 landslide at Wayanad in Kerala, India. Image copyright Planet Labs, used with permission, captured on 12 August 2024. Credit: Planet Labs image of the populated area of the 30 July 2024 landslide at Wayanad in Kerala, India.
Interestingly, the debris flow appears to have been much less intense downstream of this point, perhaps suggesting that much of the mineral content stalled in this area.
CCTV footage captured in shops struck by the landslide shows the terrible impact of this landslide:-
An initial study has now been undertaken of the meterological conditions that triggered this landslide by the World Weather Attribution network. They have concluded that climate change is likely to have increased the intensity of the rainfall by about 10%. Given the extreme sensitivity of slopes to the most intense rainfall events, this is likely to have been significant.
Reference
Planet Team (2024). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/
Text © 2023. The authors. CC BY-NC-ND 3.0Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.
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