10 January 2022
The fatal flexural topple at Canyon de Furnas in Brazil
Posted by Dave Petley
The fatal flexural topple at Cânyon de Furnas in Brazil
Many thanks to the various people who have contacted me over the weekend about the fatal flexural topple at Canyon de Furnas in Brazil on Saturday morning (8 January 2022), as shown in the image above. This event, which was caught on a dramatic video, has received considerable attention in part because of the spectacular nature of the event and in part because of the human cost.
The recording of the event can be seen at the start of the video below (I advise discretion in watching this video, the latter stages are quite harrowing):-
The failure itself is a classic flexural topple, in which failure is dominated by vertical or near-vertical structures in the rock mass. The second part of the video also captures the minute or so leading up to the main failure, in which the rock mass is (with hindsight) progressively deforming, generating a succession of rockfalls. This precursory activity is common. Once again the message needs to be that if a rock slope is generating a succession of rockfalls then a large failure event might be developing.
The video below shows the event from a more distant angle:
This video captures the fragmentation of the rock mass after impact with the water, which meant that there was fly rock affecting the boats located at a greater distance from the topple itself.
The toll from the tragic event was ten people killed and 27 people injured. Reports indicate that all ten fatalities occurred on a single boat, which appeared to be struck directly by the rock pillar. Three other boats were affected.
The location of the event is -20.646, -46.265. The site is a part of a reservoir created by the large Furnas Dam on the Rio Grande just downstream of Canyon de Furnas. The event occurred after heavy rainfall and at a time when the water level behind the dam was high.
It was the timing of the event that, in part, led to the tragedy. That the failure occurred on a Saturday morning meant that there were far more people in the path of the failure than would be case on many other occasions.
I wonder how/if the increased flow from the waterfall fits into this mess.
I also note all those UNUSED flotation vests………..
In the first video, the discharge of the waterfall increases dramatically from 0:23 to 0:33 – moments before the failure. In fact, this is captioned in the video. Perhaps it was a flash flood? It’s difficult to see how it might be related to the cliff collapse, but it’s an odd coincidence. Could vibrations from the sudden increase in flow have been enough to initiate the failure?
A tragedy. Something fully possible to be avoided with mapping, inspections and maintenance. I saw once the use of hydraulic equipment for induced toppling in European roads. A safe and effective way to reduce risk.
Here in Brazil those equipments were used it in the first years of reservoir…. Surely needed to be continued.
Maybe it can be considered one of the triggers
I would say that it was not flexural toppling, but block toppling. The columnar block tilted and collapsed.