12 June 2019
The 2017 Nayong rock avalanche: an analysis using drone and seismic data
On 28 August 2017 a catastrophic landslide (now known as the Nayong rock avalanche) occurred in Guizhou Province, China, causing multiple fatalities. I covered this event at the time, noting that remarkable footage had been collected of the event both from the ground and, astonishingly, from a drone. This rock avalanche has been analysed in detail in a new paper (Zhu et al. 2019) published in the journal Engineering Geology. Interestingly, the authors have combined the seismic data with the drone video to understand the dynamics of the failure. I believe that this is the first time an analysis like this has been undertaken.
This is an image from Zhu et al. (2019) showing the aftermath of the Nayong rock avalanche:-
The image shows that this was a catastrophic collapse of a limestone rock slope. The landslide occurred as five discreet events recorded by the drone, with the fifth being the largest. According to Zhu et al. (2019), this had a volume of about 490,000 m³, which then entrained a further 310,000 m³ from the slope. The rock avalanche descended a total vertical distance of 280 m, and travelled for a total distance of 820 m. It killed 35 people.
I think the most interesting aspect of this paper is seen in the seismic signal, and corroborated by the drone footage:-
The seismic signal shows the first detected collapse event occurring shortly before 10:18, before the first major event, seen in the drone footage, just after 10:20. The seismic signal shows that the landslide was generating a series of small seismic signals, which are presumably indications of fracture and collapse occurring within the landslide mass as it began to fail. We have seen this pattern previously, and once again emphasises that rock slope failure is a time dependent process in which the final collapse is simply the final manifestation of long-term deformation and rock fracture. It is this phenomenon that allows the forecasting of some rock collapse events, if suitable instrumentation is deployed.
Zhu, Y., Xu, S., Zhuang, Y., Dai, X and Xing, A. 2019. Analysis of characteristics and runout behaviour of the disastrous 28 August 2017 rock avalanche in Nayong, Guizhou, China. Engineering Geology. Doi: https://doi.org/10.1016/j.enggeo.2019.105154