Bowing
The Landslide Blog is written by Dave Petley, who is widely recognized as a world leader in the study and management of landslides.
One of the most significant landslide events of 2024 to date occurred on 30 July in western India. On this date, heavy rainfall triggered multiple landslides in Kerala, of which the most significant was the so-called Wayanad landslide. Immediately after the disaster, I posted an initial report, followed by a more reflective piece and finally a Planet Labs image of the site. As a reminder, this is the Planet Labs image (the marker indicates the landslide source):-
I also provided a rough image compare with another Planet Labs image, captured on 6 March 2024:-
As always, my blog posts are provisional, with the definitive reports coming from the peer reviewed literature. The journal Landslides has just posted a paper (Das 2024) that provides a first proper analysis of the Wayanad landslide (which is also known as the Vellarimala landslide).
Das (2024) examines the rainfall event that triggered the failure. A local rain gauge, at Thettamala, recorded 409 mm of rainfall in the 24 hours up to 8:30 am on 30 July (the landslide occurred at 2 am that day), an unusually high total even in the monsoonal area.
The resultant landslide extended 8 km, having started in a source area that had suffered previous failures. The surface area of the source zone was 86,000 m2, comprising of shallow, weathered deposits. This initial failure transitioned into a channelised debris flow, which in places had a depth of 7.5 metres. It is unsurprising that the impact on the communities located along the channel was devastating, most notably on Chooralmala, which lay directly in the path of the flow.
Das (2024) considers the factors that played in a role in the causation of the Wayanad landslide. Key issues may have been the loss of forests, the nature of the geology and the steep topography. This requires a more detailed analysis in due course.
The paper also briefly considers the psychological impact of the landslide on the survivors:-
“Survivors, many of whom are grappling with severe physical injuries, face an even greater battle against the mental trauma that now haunts them. For those who have lost everything, including their loved ones, the path to recovery seems impossible. Sleepless nights and a crippling fear of rain will now a part of their reality. While discussions around rehabilitation are ongoing, the psychological scars of such a disaster cannot be easily mended. The Kerala Health Department deployed a 121-member team of psychiatrists, clinical psychologists, psychiatric social workers, and counselors soon after the disaster to provide immediate and long-term mental health support.”
This is a much neglected topic for disasters in general, and landslides specifically. A rainfall induced catastrophic debris flow at 2 am is a horrific prospect – it is unsurprising that the survivors will be traumatised in subsequent monsoon rainfall.
References
Das, R. 2024. Catastrophic landslide in Wayanad district of Kerala, India on July 30, 2024: A complex interplay between geology, geomorphology, and climate. Landslides. https://doi.org/10.1007/s10346-024-02385-8
Planet Team 2024. Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/
