|MadSci Network: Earth Sciences|
Dear William, I imagine that your question was sparked by the recent media coverage of the risk of a huge landslide at La Palma, in which a giant slice of the island would slide into the sea creating a tsunami (tidal wave). First of all, geological events of this magnitude have occurred throughout the history of the Earth, but they tend to be very infrequent by human standards. The prediction that this event will happen does not mean it is going to happen soon, or perhaps even for thousands of years – if at all! The prediction that the mountain might collapse was made by geologists some time ago, but only picked up by the media this summer, probably to fill newspapers when there wasn’t much news! That said, it would be impossible and probably unwise to try to prevent it by the means you suggest. The prediction is that a volcanic eruption could inject water under high pressure into the rocks, and that the pressure and addition of fluid could overcome friction on the rift and trigger the collapse. You must appreciate the size of the mountain to see why it is not practical to remove the area at risk. The unstable mountainside sits on a large geological rift zone that runs through the mountain. The unstable area is something like 30 km long and 10+ km wide, a huge area, and the rift will run through the mountain to a depth possibly of several kilometres. To get a view of the scale, go to the following website and look up La Palma, where you will find a map of the island showing the rift zone: http://volcano.und.nodak.edu/ To remove the mountainside by mechanical means would be an impossibly huge task, like taking Mount Everest apart with jackhammers and dynamite! Drilling explosives deep into the mountain would risk setting off the very landslide we want to prevent. I think that we have to accept that large-scale geological catastrophes are part of the risk of living on planet Earth. Thankfully the largest events occur only infrequently. For example, there is a type of volcano called a collapsed caldera, of which there are many dozens on Earth. On average one of these can be expected to erupt every few tens of thousands of years – when they occur they are titanic in scale, and have severe effects on global climate for decades, not to mention the destruction for hundreds or thousands of miles around them, but we will probably not see one in our lifetimes. The possibility of the La Palma mountainside sliding into the sea should be ranked as one of these rare, though potentially devastating, events. The best thing we can do is hope that it doesn’t happen in our lifetime, and that hope is probably well founded. I hope this answers your question. With best wishes, David Scarboro
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