21 January 2016

Landslides in Chile Part 3: the Meson Alto rock avalanche

Posted by dr-dave

 The Meson Alto rock avalanche

A few kilometres upstream from the Las Cortaderas rock avalanche lies one of the truly great landslides, the Meson Alto rock avalanche.  This landslide is so large – 4.5 cubic kilometres, which is more than 10 billion tonnes of rock – that it can only really be shown properly on a satellite image:

Meson Alto rock avalanche

Meson Alto rock avalanche via Google Earth

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I have annotated the Google Earth image below to show the main features of the landslide.  Note that the boundaries are approximate, particularly on the downstream part of the deposit, where there may be a combination of rock avalanche deposits and redeposited landslide material from the outburst flood:

Meson Alto rock avalanche

The Meson Alto Rock Avalanche via Google Earth, annotated to show the main features

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The landslide scar is very clear, as is the huge landslide deposit.  Note the way that it has spread downstream.  The rock avalanche is described in detail in a great paper, available online, by Deckart et al. (2014).  They point out that this is a rock avalanche that has been deposited on top of glacial moraine.  The landslide is believed to have occurred about 4,500 years ago.  This is the landslide from downstream:

Meson Alt0 rock avalanche

Meson Alto rock avalanche from downstream

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Note the fluvial (river) terraces between the camera and the deposit in the background.  These may be a combination of the lake deposits from the Las Cortederas landslide and the flood terraces from the breach of the Meson Alto rock avalanche.  This is the artificial dam that has been built to create a lake at the site of a previous natural lake impounded by the landslide.  At some point the natural lake must have drained through a substantial breach event:

Meson Alto rock avalanche

The artificial rock dam at the site of the Meson Alto rock avalanche

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The landslide deposit is the huge pile of debris in the background,  Note how large the dam is in this image – compare that with the Google Earth image above.  This gives an idea of the scale of this landslide.  Capturing the scale of the landslide is extremely difficult.  This is an attempt at a composite image to take in all of the landslide features, taken from the banks of the lake:

Alton Meso rock avalanche

Alton Meso rock avalanche

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Part of the landslide scar is on the left of the image, and the landslide extends across the image to the rock slope on the right side.  The dam blocks the space between the mound of debris and the rock wall on the left side of the image.

Reference

Deckart, K., Pinochet, K., Sepulveda, S., Pinto, L., and Moreiras, S. 2014. New insights on the origin of the Meson Alto deposit, Yeso Valley, central Chile: A composite deposit of glacial and landslide processes? Andean Geology 41 (1): 248-258/