Scattered across the world’s oceans are a handful of rare geological time-bombs.
Once unleashed they create an extraordinary phenomenon, a gigantic
tidal wave, far bigger than any normal tsunami, able to cross oceans
and ravage countries on the other side of the world. Only recently
have scientists realised the next episode is likely to begin at
the Canary Islands, off North Africa, where a wall of water will
one day be created which will race across the entire Atlantic ocean
at the speed of a jet airliner to devastate the east coast of the
United States. America will have been struck by a mega-tsunami.
Back in 1953 two geologists
travelled to a remote bay in Alaska looking for oil. They gradually
realised that in the past the bay had been struck by huge waves,
and wondered what could have possibly caused them. Five years later,
they got their answer. In 1958 there was a landslide, in which a
towering cliff collapsed into the bay, creating a wave half a kilometre
high, higher than any skyscraper on Earth. The true destructive
potential of landslide-generated tsunami, which scientists named
"Mega-tsunami", suddenly began to be appreciated. If a modest-sized
landslide in Alaska could create a wave of this size, what havoc
could a really huge landslide cause?
Scientists now realise that the greatest danger comes from large
volcanic islands, which are particularly prone to these massive
landslides. Geologists began to look for evidence of past landslides
on the sea bed, and what they saw astonished them. The sea floor
around Hawaii, for instance, was covered with the remains of millions
of years’ worth of ancient landslides, colossal in size.
But huge landslides and
the mega-tsunami that they cause are extremely rare - the last one
happened 4,000 years ago on the island of Réunion. The growing concern
is that the ideal conditions for just such a landslide - and consequent
mega-tsunami - now exist on the island of La Palma in the Canaries.
In 1949 the southern volcano on the island erupted. During the eruption
an enormous crack appeared across one side of the volcano, as the
western half slipped a few metres towards the Atlantic before stopping
in its tracks. Although the volcano presents no danger while it
is quiescent, scientists believe the western flank will give way
completely during some future eruption on the summit of the volcano.
In other words, any time in the next few thousand years a huge section
of southern La Palma, weighing 500 thousand million tonnes, will
fall into the Atlantic ocean.
What will happen when the
volcano on La Palma collapses? Scientists predict that it will generate
a wave that will be almost inconceivably destructive, far bigger
than anything ever witnessed in modern times. It will surge across
the entire Atlantic in a matter of hours, engulfing the whole US
east coast, sweeping away everything in its path up to 20km inland.
Boston would be hit first, followed by New York, then all the way
down the coast to Miami and the Caribbean.
Mega-tsunami: La ola de la destrucción (In Spanish)
Tsunami: Anatomy of a Disaster
Mega-tsunami: Questions and Answers