Yerba Loca – an interesting rockslide in central Chile

In a new paper published in the journal Landslides, Sepulveda et al. (2020) describe an interesting large rockslide in the central Andes of Chile. This is a large failure, about 2.5 million cubic metres, in volcanic rocks.

The site has a good set of images of the landslide site, both before and after the failure.  This is the site prior to the failure event:

The site of the Yerba Loca rockslide prior to failure, via Google Earth

.

And this is the site after failure:

The site of the Yerba Loca rockslide after failure, via Google Earth

.

The slope, which is located at about 4000 metres above sea level, failed over a period of several days between 14 and 30 August 2018.  Note however that Sepulveda et al. (2020) rightly point out that tension cracks are clearly visible in the images prior to failure (look at the area in the first image in which the rear scarp finally formed), suggesting that this was a progressive failure event.  The authors note that these cracks are visible in satellite imagery right back to 2003. No clear trigger event precipitated the landslide, with failure occurring some weeks after heavy rainfall and snow melt.  As such this is a classic progressive failure.

Sepulveda et al. (2020) have used InSAR to examine the development of the slope in the years prior to failure.  This is one of the most interesting aspects of the InSAR technique – the ability to go back through the archive to understand the evolution of failure is fascinating.  They found that movement was evident over the three year period leading up to failure, with movement rates reaching 10 centimetres per year in the seven months before the collapse.

The InSAR data also suggests that the landslide is continuing to move and that the area of deformation is expanding.  Sepulveda et al. (2020) suggest that there is the possibility of a larger collapse:

“The active rock slide may derive in catastrophic failure in the near future, becoming a rock avalanche. Continuing deformations to the north-west and south of the 2018 landslide suggest that the landslide mass may grow in volume. Depending on the amount of available water in the form of snow or ice, the avalanche may derive into a debris flow that may potentially reach the Mapocho river and human settlements downstream”

Monitoring of this site is going to be important in the long term.

Reference

Sepúlveda, S.A., Alfaro, A., Lara, M. et al. 2020. An active large rock slide in the Andean paraglacial environment: the Yerba Loca landslide, central Chile. Landslides (2020). https://doi.org/10.1007/s10346-020-01564-7