A Catastrophic Glacier Collapse and Mudflow in Salkantay, Peru

On 23 February 2020 (corrected – this was erroneously reported as 24 February 2020) an enormous, catastrophic debris flow tore down the Salkantay River in Santa Teresa, Peru. This event has killed at least four people, with a further 13 reported to be missing. Given the magnitude of the flow, this number is probably uncertain.

The mudflow was captured in an extraordinary video posted to YouTube:

A mudflow on this scale usually requires an extraordinary cause.  Diario Correo in Peru has an explanation – this event was caused by glacial collapse on Salkantay mountain.  This hypothesis is proposed by Oscar Vilca Gómez, who the article describes as a specialist in Hydrology and Glaciology.  He visited the site site of the detachment as part of a research team from the National Institute for Glacier Research of the Ministry of Environment.  They propose that an ice / rock avalanche detached from the mountain, crossed the Salkantay Cocha lake, and generated the huge debris flow.

The article includes the following image of the site:

The site of the rock / ice avalanche at Salkantay in Peru. Image by Benito Moncado via Diario Correo Peru

In first inspection this appears to be a wedge failure in the rock mass that has fragmented to generate the rock / ice avalanche. The photographer appears to be standing on the landslide deposit.

Salkantay (which also appears to be named Salcantay at times) is located at -13.340, -72.540.  Salkantay Cocha lake appears to be at -13.342, -72.569.  At the moment it is not clear as to which slope has failed to generate this ice-rock avalanche and debris flow.  There is excellent Google Earth imagery of this area, so it should be possible to get a better understanding in due course.

At the moment details of this very significant event are somewhat unclear; I hope that more details will emerge. This event is reminiscent of the 2012 Gayari ice and rock avalanche in Pakistan and the 2017 Villa Santa Lucia landslide in Chile.

UPDATE: 28 February

Over the last 24 hours more information has become available about the Salkantay landslide and mudflow. Oscar Vilca has kindly contacted me to say that the event occurred on 23 February 2020, and not 24 February as had been widely reported.

The triggering event is being described as an ice/rock avalanche with an initial volume of 400,000 cubic metres. This has clearly bulked up to form a mudflow with a much higher volume, presumably through entrainment of ice and saturated debris in the channel. This is similar to the Seti River rock avalanche and debris in Nepal in 2014, which also had devastating effects.  On this occasion the initial collapse may have been smaller, but the mudflow was on a similar scale.

On Twitter, Julio Montenegro G. has posted an interpretation of the event, based upon an image of the scar, which has then been located on pre-event imagery:

I am not sure as to the origin of the image that shows the scar of the initial failure, but a better version was posted to Twitter by Turismo Peru:

The scar of the Salkantay landslide, posted to Twitter by Turismo Peru.

If this is indeed the scar then my interpretation is that this is a classic wedge failure in the rock mass, with a near vertical fall onto the ice and moraine at the toe of the slope. The rock slope would have been a mixture of rock and ice, both on the surface and within fractures. On impact the mass has probably fragmented to form an ice/rock avalanche, which has then entrained debris and ice/snow/water, transitioning to become the mudflow seen in the videos. This has behaved in a manner that is akin to a lahar, with a large volume, high velocity and long runout.

Reports suggest that Salkantay Cocha lake remains intact, but that waves within the lake, generated by the landslide, have caused some erosion of the moraine dam.  This now needs to be monitored. There are of course some real human tragedies in this disaster.  The estimated human cost appears to be 13 people.

This post was written by Dave Petley and originally published on The Landslide Blog, an American Geophysical Union Blog.