The 13 October 2020 landslide in Phong Dien, Vietnam, triggered by an extraordinary rainfall event

On 13 October 2020 heavy rainfall triggered a rapid landslide at Phong Dien in Thua Thien Hue, Vietnam.  I covered this event at the time – it was a double tragedy as the landslide killed 13 members of a rescue team en route to another landslide accident.  A paper (Van Tien et al. 2021) has just been published in the journal Landslides that provides a description of this event.

The events started with a landslide at the construction site of the Rao Trang-3 hydropower plant on 12 October 2020.  This landslide killed 17 people.  A rescue team was dispatched to assist in the rescue and recovery operation.  The team stopped for the night at a location that is described as Ranger Station-7, situated in Phong Dien, c.10 km from the Rao Trang-3 site.

Van Tien et al. (2021) describe an extraordinary amount of rainfall.  At the nearby A Luoi rainfall station, a total of 2190.2 mm was recorded in the period 6-12 October 2020.  The landslide at Ranger Station-7 occurred at midnight on 13 October.  The landslide is located at 16.434°, 107.311°. The Google Earth image below, collected in February 2021, shows the aftermath of the landslide:-

Google Earth image of the 13 October 2020, deadly landslide in Phong Dien, Vietnam.

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Perhaps surprisingly, Van Tien et al. (2021) describe the initial failure, at the top of the slope, as being rotational:

The landslide was characterized as a rotational type with a visible sliding surface, head scarp, and flanks in the upper slope area. The landslide took place on an average slope of 21° with a poor vegetation cover. The lower slope is quite gentle, with an angle of 18°, while the slope angle of the upper part is 27°.

The landslide length was 546 m, with a volume of 81,500 m³.

The authors suggest that failure occurred initially in a block downslope of the final crown of the landslide – a section that they call Block I:-

The failure process of the 13 October 2020, deadly landslide in Phong Dien, Vietnam. Diagram from Van Tien et al. (2021).

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About 5 minutes later Block II failed due to the loss of toe support.  Van Tien et al. (2021) suggest that the landslide was highly mobile, moving at 29 m/sec.  Only eight of the 21 people in the Ranger Station survived, all with injuries.

This extraordinary rainfall event triggered many other landslides in the Phong Dien area, as the image below shows.  Some appear to have had quite high mobility:-

Google Earth image of landslides triggered by the October 2020 rain event in Phong Dien, Vietnam.

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Reference

Van Tien, P., Trinh, P.T., Luong, L.H. et al. 2021. The October 13, 2020, deadly rapid landslide triggered by heavy rainfall in Phong Dien, Thua Thien Hue, Vietnam. Landslides. https://doi.org/10.1007/s10346-021-01663-z