Bowing
The Landslide Blog is written by Dave Petley, who is widely recognized as a world leader in the study and management of landslides.
On 23 August 2024, heavy rainfall triggered a landslide at Nakkerd Hill (also known as Nak Koet hill) in the Mueng distruct of Phuket, Thailand. The landslide was a channelised debris flow that swept onto houses located at the foot of the slope. In total, 13 people were killed, with a further 19 injured.
Khaosod has posted a drone video showing the landslide site:-
This video starts at the foot of the slope, showing the destruction to the houses, but then follows the track of the landslide to the source. The latter part of the video shows the impact on the houses below. It is a remarkably good resource.
The location of the crown of the landslide is approximately [7.8275, 98.3111]. The still from the drone footage below shows the upper portion of this most interesting failure:-
The image below shows the crown area:-
The buildings at the top of the hill are part of a temple complex associated with Phra Phuttha Mingmongkol Eknakiri, or the Great Buddha, a well-known landmark at the top of Nakkerd. As the images show, the landslide started as a shallow slip in weathered granitic rocks, a few metres downslope from a car park that forms a part of the complex. This small slip rapidly entrained a large amount of debris downslope, stripping the regolith back to the bedrock interface. Note how the width of the landslide widens along the track.
As the gradient of the slope reduced, the landslide entered an existing drainage line, which directed it into the houses lower on the slope, where the fatalities occurred. The Google Earth image below shows the site; the houses just to the right of the sharp bend in the road were impacted by the landslide:-
In the aftermath of the landslide, there has rightly been a great deal of focus on the role of the development of the temple in the triggering of the Nakkerd Hill landslide. This quote, from a very good news report on 27 August 2024, highlights the concerns:-
“On August 27, Col. Dusit Kaesonkaew, head of the team investigating and resolving state land encroachment and natural resource destruction in the 4th Army Area, revealed that construction at the Big Buddha site began in 2005. He noted that the project failed to implement proper water division techniques, contrary to highland construction engineering principles.”
This seems to me to correctly focus on the most likely cause of the landslide, although I would also wonder if there was some dumping of waste or fill onto the slope too, which might have loaded the slope? There has also been a suggestion that removal of trees may have played a role. News reports indicate that the Foundation responsible for the temple has been charged with forest encroachment and unauthorised construction.
In addition though, some consideration is probably needed of the construction of houses lower down the slope. As the Google Earth image shows, they were situated in a zone that appears to have a high level of hazard. The houses were constructed after 2008. Keeping people safe from landslides involves both the management of slopes and the avoidance of placing assets in hazardous locations.
As rainfall intensities continue to increase due to our warming planet, ensuring that vulnerable communities are not in the path of landslides is going to be a vital part of risk reduction.
