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Unlike most tsunamis, which are caused by underwater tectonic activity, megatsunamis are usually the result of enormous debris from volcanic activity impacting water
Scientists have uncovered evidence that suggests a prehistoric megatsunami occurred off the coast of the Cape Verde Islands around 70,000 years ago. It is hypothesized that the wave reached the height of 800 feet (~244 meters) and was most probably caused by the collapse of a volcano.
The new theory was proposed when researchers discovered extremely large boulders in the area, nearly 2,000 feet inland. The specific boulders were made of marine rock, while all surrounding terrain consisted of volcanic rock. Scientists have determined that these were most likely deposited there by a massive wave. The extreme height of the megatsunami was calculated after determining the weight of the rocks and estimating the force needed to drift them this far inland.
Volcanic collapse usually leads to landslide, which in severe cases can cause mega-waves of varying severity, depending on circumstances. The new theory says that the megatsunami was so powerful that it surpassed the height of a 600 foot cliff, surging over it and ultimately maintaining its 800 feet force above sea level.
Leading researcher Ricardo Ramalho says by displacing a huge mass, this will generate powerful movement of water and
“in the case of volcanic flank collapses they can be very acute, because you have all this mass collapsing basically into oceans.”
Ramalho claims the new discovery was made entirely by chance, when witnessing the huge boulders on top a high plateau. No other theory could have explained how they got there, so researchers concluded that they were brought upon by a wave of enormous size.
Scientists have also used cosmogenic dating to determine the age of the rocks. The cosmogenic technique takes into account the manner in which cosmic rays bombard the Earth and create unique isotopes on terrain and rock surfaces. The 700-ton boulders have been dated to a period from 70,000 to 73,000 years ago, when the megatsunami is hypothesized to have occurred.
“You can only explain the existence of those deposits from the impact of a giant tsunami approaching from the western side of the island,” said Ramalho.
As in the case of most natural disasters, megatsunamis cannot be prevented through the aid of technology. Ramalho says the further research is needed to determine what causes flank collapse in order to properly understand such natural hazards. He has also argued in favor of improving advanced monitoring networks to detect volcanic unrest and provide additional warning time in case of a collapse.
Photo Credits: Pixabay
