The Landslide Blog is written by Dave Petley, who is widely recognized as a world leader in the study and management of landslides.
On 17 December 2017, a large landslide was triggered at Santa Lucía in the northern Patagonian Andes of Chile. An initial rock slope failure transitioned into a 12 km long debris flow that struck Santa Lucía, destroying half of the village with the loss of 22 lives. The Google Earth image below shows the aftermath of the landslide:-
Such events are difficult to anticipate due to the complexity of both the failure processes and the transition from one landslide type to another. Therefore, analysing such failures is a key tool as we seek to reduce risk.
A very nice paper (Singh and Sepúlveda 2024) has just been published in the journal Landslides that looks at the initial failure mechanisms of this event. The image compare below shows Google Earth imagery from 2006 (pre-failure) and 2021 (post-failure):-
The most obvious change between the images is a big chunk of the steep rear scarp that is missing post-failure in the centre of the second image. Singh and Sepúlveda (2024) describe this as a secondary failure. The main block that failed is on the left side. The total volume of the failure was 12.5 million m3 from the primary and secondary failures combined.
The landslide was controlled by a set of pre-existing discontinuities – Singh and Sepúlveda (2024) suggest that this started as a wedge failure towards the toe of the main mass, which then propagated upwards (i.e. the landslide retrogressed).
The landslide was preconditioned by progressive damage by glacial loading and unloading. The final failure was triggered by extremely heavy rainfall associated with an “atmospheric river” event. That rainfall played such a key role does support the idea that failure was initiated lower on the slope.
As rainfall intensity will continue to increase in much of the world in the coming years as a result of climate change, aided by permafrost degradation in high elevation locations, such events are likely to become more common. This analysis of the 17 December 2017 Santa Lucía landslide is a welcome contribution as we seek to determine where and when such events will occur.
Reference
Singh, J. and Sepúlveda, S.A. 2024. Understanding the failure mechanisms of the 2017 Santa Lucía landslide, Patagonian Andes, using remote sensing and 3D numerical modelling techniques. Landslides. https://doi.org/10.1007/s10346-024-02346-1
