You've probably never heard of Cumbre Vieja, but it could be responsible for the worst natural disaster in recorded history at some point in the near or not-so-near future.

The island of La Palma, one of the Canary Islands, is composed of two big volcanoes, the southern one of which is the Cumbre Vieja, which is still active. In fact, it erupted most recently in 1949, and this is part of the problem. During the 1949 eruption a huge crack appeared, running almost the entire length of the island, and the whole western half of La Palma slid a few metres towards the sea and then stopped.

So far so good. However, a research team consisting of Dr Simon Day of University College London and Dr Steven Ward of the University of California has discovered that the island will one day collapse along this fault line, possibly when the next eruption happens, possibly sooner due to the building stress of water entering the fault, becoming superheated by the volcano, and expanding. When this collapse happens, a mass of rock twice the size of the Isle of Man will fall into the sea, releasing energy equivalent to half the annual electricity consumption of the United States of America.

Still wondering what the big deal is? Especially as there is no agreement on when exactly this might happen? The scale of the danger didn't really come to light fully until Day and Ward analyzed the effects of a large mass of rock falling into the sea.

Most people have heard of tsunami. They are giant, fast-moving waves, several metres high, which are triggered by earthquakes or volcanic eruptions, and can cause devastation to coastal areas they hit. Tsunami caused by earthquakes or volcanoes have been well-studied, but no one had ever studied the particular effect of a very large mass actually falling into the sea, until recently. The predictions of Day and Ward, based on their experimental models, are startling and worrying:

  • Immediately after the collapse of Cumbre Vieja, a 'dome' of displaced water 900 metres high and many kilometres wide will form, and then rebound.
  • The resulting tsunami will be incredibly powerful, further fuelled by the continued slide of the land mass underwater, and will cross 250 kilometres in 10 minutes.
  • Waves up to 100 metres high will hit the West Saharan shore. Let's say that again. 100 metres. That doesn't seem very far when you're running it, but it would seem pretty damn high if you saw it about to fall on top of you.
  • The coast of Brazil will be hit by 40-metre waves.
  • The entire Eastern seaboard of North America will be hit by waves of up to 50 metres in height, which will travel several miles inland.

Did that get your attention? Doesn't seem real, does it? Yes: because of the amplitude and exceptionally long wavelength of the waves caused by the island's collapse, the 'mega tsunami' will complete inundate most of the cities of the East coast of the US. Economic damage estimates are difficult to gauge, as one might expect, but are expected to be "in the multi-trillion dollar range".

Any good news? Well, some.

  • Cumbre Vieja is not currently erupting. Eruptions occur at intervals of several decades to a century. In other words, it could be tomorrow, or it could be 2097. Not much of a comfort maybe, but there it is.
  • There should be a period of days or even weeks where there are warning signs, shifts in the rock, excessive heating, which will allow early warning systems to go into action and emergency plans to be made in advance.
  • Even after the collapse it will take several hours for the tsunami to reach most inhabited places, giving time for evacuation.
  • Europe will also be hit along its Atlantic coast, but by much smaller tsunami which should not cause such great devastation.

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