20 January 2016

Landslides in Chile Part 2: Las Cortaderas

Posted by dr-dave

Landslides in Chile Part 2: Las Cortaderas Landslide

Located not far from Santiago, in the upper reaches of the Maipo River catchment, is a very large mass movement, known as the Las Cortaderas Landslide.  This is a fascinating landslide, not least because there are two distinct phases.  The main landslide is vast – an ancient rock avalanche that entered the valley at some point in the past (of which more below).  The frontal portion of this landslide deposit then failed again in the 1958 Las Melosas earthquake, blocking the Yeso River.  This makes the later landslide sound like a small event – it is certainly not.  Sepulveda et al. (2008) estimated that it had a volume of 15 to 20 million cubic metres, which is a large landslide by any standard.   The river was blocked for a few years before breaching naturally.  This is a view of the landslide from upstream:

La Cortaderas landslide

Las Cortaderas Landslide from upstream

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To illustrate the features of the lower part of the landslide, I have annotated the photograph below:

La Cortaderas landslide

Annotated image of the Las Cortaderas Landslide

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This image shows the landslide scar with the deposit on the right hand side (the scar is just to the left of the power cables):

The source of the La Cortaderas landslide

Las Cortaderas Landslide

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But, as mentioned above, the 1958 La Cortaderas landslide is a comparatively small failure of the deposit of a much larger landslide body.  This is the Google Earth image of the site – I have annotated the 1958 landslide and the larger rock avalanche deposit from which it originated:-

La Cortaderas Landslide

Las Cortaderas Landslide via Google Earth

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Taking a wider view though, the scale of the ancient rock avalanche becomes clear:

Las Cortaderas landslide

Las Cortaderas Landslide

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This is a truly huge landslide that would have blocked the river before breaching.  The current river cuts through the landslide deposit, leaving a portion of the deposit on the other side of the valley.  This is clearly exposed by the river.  Note the chaotic landslide deposit, with the predominance of the largest boulders occurring in the upper portions:-

La Cortaderas Landslide deposit

Las Cortaderas Landslide deposit

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But if you think this is large, you should see what lies upstream – of which more tomorrow.