Volcanoes have this annoying habit of becoming unstable. They build themselves up vertically, piling up lava flows on the top of the cone, until every so often gravity wins.
Volcanic collapse happens for a number of reasons. The biggest recorded avalanche in modern history happened because of a volcano; the entire north side of Mount St. Helens collapsed in 1980 due to pressure within the volcano that was deforming the entire mountain.
Other types of collapses are associated with the building of a high peak or a lava dome. When thick, viscous lava is pushed out of a volcano, it starts building lava domes that build upwards. A big, vertical pile of rocks isn’t a stable situation and can lead to a collapse. This image from the International Space Station shows the remnants of an ancient volcanic collapse in the nation of Bolivia. The mountain close to the center of this image is called Tata Sabaya. It’s one of many volcanoes in this part of the world, occurring due to subduction off of the West coast of South America.
However, take a look to the west of this cone. First, you can see the dried, salty remnants of a lakebed called Salar de Coipasa, which was filled with water during the last glacial period (10,000 years or more ago, at the time it would have been Lago Coipasa). Today, that lake has mostly dried up, leaving a salt flat deposit…but there are all these giant pieces of rock sticking out.
These blocks are surrounded by the saline deposits, but they spread over an area of 300 square kilometers. For comparison, that’s over 3 times the size of manhattan. The largest blocks stand up to 100 meters above the surrounding terrain; basically they’re skyscrapers.
These giant blocks are the remnants of a mega-landslide. The Tata Sabaya volcano, sometime before the last glacial maximum, completely collapsed, spilling its innards to the west and into the lake. Whether this collapse happened during an active eruption or just because of gravity (or gravity + an earthquake) is difficult to tell, because all of the other remnants of this avalanche wound up in the lake and washed away. Since the collapse, the volcano has rebuilt itself into a mountain probably similar in size to what it used to be. But at least from this perspective, the remnants of this mega-avalanche are a sight to behold.
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