What is a mega-tsunami?
A mega-tsunami is simply a gigantic wave, one big enough to cross oceans and destroy cities. They can be thousands of feet high moving at supersonic speeds. They can be caused by huge meteors crashing into the ocean, or by massive landslides. No boat or building hit by a mega tsunami could survive. But now scientists believe that we could be sitting on a time bomb, that sooner or later one will destroy New York, Boston and Miami, and that nothing could stop it.
When was the biggest tsunami?
The largest tsunami in recorded history was in Lituya Bay, Canada, 1958. An earthquake measuring 8.3 on the Richter scale caused 40 million cubic metres of rock to fall into the sea. A wave more than half a kilometre high was created that surged through the bay devastating all in its path. This was not even a mega-tsunami, by these standards it was tiny, but it did show scientists what sort of wave a small landslide could cause. But what would be the effect of a big one?
Where have mega tsunamis occurred in the past?
Scientists hunted that world for sites that could potentially cause a mega tsunami. They discovered that at least eleven mega tsunamis had happened in the last 200,000 years, caused by island collapses in the Hawaiian and Canary islands.
Where is one likely to occur in the future?
The island of La Palma, in the Canary Islands off the coast of North Africa, was discovered to be in great danger of collapsing. The island is volcanic and during an eruption of the Cumbre Vieja volcano in 1949 part of the island slipped a few metres into the sea before stopping. Another eruption could cause the western flank of the island to collapse in the Atlantic Ocean.
When will it happen?
No one knows. It will happen during an eruption of Cumbre Vieja. It is an active volcano, last erupting in 1949. However the next eruption may not destroy the island, the next 10 may not. Only on thing is certain - one-day an incredible force will surge through the Atlantic Ocean.
How big would it be?
It would be far bigger than any wave ever seen for thousands of years. 500 billion tonnes of rock are waiting to collapse into the ocean at terrific speed. The collapse would create nearly 5,000,000,000,000,000 (5 thousand trillion) joules of kinetic energy, which would be converted into a colossal wave 900 metres high with awesome speed - within ten minutes it would have moved 250 kilometres. The landslide would continue to move underwater, powering the wave as it goes.
What damage would it cause?
No coastline in the North Atlantic would be spared. Britain, France, Spain and Portugal would all be badly hit North Africa would be hit by 100 metre waves, but the main wave would travel west. It would storm across the Atlantic in hours, hitting the Caribbean and Brazil badly. However, the real damage would be to the East coast of the USA.
By the time it had travelled the 4000 miles to America the wave would be lower and wider. It would now be just 50 metres high but many kilometres long, allowing it to sweep up to 20 miles in land, destroying everything in its path. Boston, New York and Miami would virtually be wiped off the map. Skyscrapers would be bulldozed as if they weren't there. Bridges would be ripped from their foundations. And virtually every human in these cities would be killed.
There would be indirect consequences around the world. The events of the 11 September wiped millions off stock markets around the world. What would be the effects of the destruction of not only the rest of New York, but also the rest of the East Coast on the world's economies?
How can we stop it?
Put simply, we can't. We have no technology that can stop a volcano erupting, no support that can hold 500 billion tonnes of rock and no barrier that can stop a wave moving at 500 miles per hour. All we can do is evacuate.
But can we evacuate tens of millions of people with just a few hours notice? Unless evacuation plans were incredibly well thought out, no. Imagine New York's grid locked streets trying to cope with every person in the city on them. The alternative is evacuating when the volcano starts to erupt, possibly giving a few weeks warning. However, the island may not collapse on the next eruption, or even the next ten. Would we risk evacuating millions of people on the off chance? Could we risk not to?