Are you ready for a Mega-Tsunami?
'Scientists simply do not know'
Imogen Tillet | 3 November 2015

It is a well known fact that volcanoes can be one of the deadliest natural disasters on earth. However, what most people do not know, is that a volcano may not only be destructive from the volume of lava and ash pumped out of it, but could also generate a much more serious hazard: a mega-tsunami.

On the Canary Island of La Palma was the steep and rapidly growing volcano, Cumbre Vieja. The 1949 eruption caused the western flank of this volcano to drop 4 metres towards the North Atlantic, and then stop. This enormous chunk of volcanic rock is estimated to have a volume of 500km (about double the size of the Isle of Man), and is now believed to be detached from the main body of the island’s volcano. When the next eruption of Cubre Vieja occurs, scientists believe that this detached portion of rock will collapse into the sea. Eruptions usually occur roughly every 200 years, so with the last eruption happening in 1949, it should be decades before the next. However, the rock collapse may not necessarily happen at the next eruption as it may take 10 or more summit eruptions for the collapse to happen; scientists simply do not know how much movement it will take. Measurements taken in the late 1990s using GPS suggested that the landslide might be slowly creeping seaward, even less than a centimetre per year. However, even if this is true, the rock mass will definitely need to be triggered by an eruption, or many, to complete its journey into the ocean.

Due to the volume and mass of the rock that will plunge into the sea, whenever the triggering eruption may be, there will be huge worldwide effects of the collapse. The western flank would slide down westwards into the Atlantic Ocean, causing many, very strong earthquakes across La Palma during this process. As the rock mass plunges into the sea, a giant wave would be created: a mega-tsunami! Within two minutes of the landslide plummeting into the sea, the initial dome of water, of almost 900 metres high, would be generated. In the following 45 minutes, waves up to 100 metres high will hit the shores off the Canary Islands, wiping out the densely populated parts of the coasts. The waves would then crash into the African mainland, before heading further north (when they will start to break down) and battering Spain and the UK with tsunamis up to 7 metres high. Meanwhile, the majority of the energy in the wave would go across the Atlantic towards the Caribbean, Bahamas and, after roughly 9 hours, the USA, with smaller waves heading other directions. Although the waves would get smaller as they travelled across the ocean, scientists believe that they could still reach up to 50 metres high when they hit coasts such as the east of the USA and North Brazil. As well as being a towering height, these waves will have wavelengths of hundreds of kilometres long. Once one hits a coast, the solid wall of water will keep coming for perhaps over 15 minutes, before taking the same time to withdraw, obliterating even the sturdiest built structures.

This event is inevitable, and when it does happen, the death toll will be millions, or even tens of millions without considerable forward planning of a coastal evacuation. The impact on the US economy will be huge, wiping out the insurance industry, and causing global economic meltdown. All this considered, even a minor geophysical event at a remote Atlantic volcano will have an effect on everyone on the planet. Although it is unlikely to occur in our lifetime, on a geological timescale, major collapses of volcanoes are very frequent, and may be even more frequent due to the current stage of global warming. Increased past volcano collapses can be linked with periods of changing sea level, and also a warmer, wetter climate. With global warming being the ultimate cause of these, the collapse of Cumbre Veija may be just around the corner...

Image used under creative commons licence.

James Routledge 2016