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Megatsunami Was 270 meters High

Science Fields

Lifted 700-ton boulders atop island…

A tsunami triggered by a massive landslide 73,000 years ago off the western coast of Africa was 270 meters in height and lifted huge rocks as heavy as 700 tons more than two hundred meters onto the plateau of a nearby island, a study conducted by an international team of scientists reveals.  

The tsunami which devastated northeastern shores of Japan, causing a massive death toll and a nuclear disaster was a “dwarf” in comparison, reaching 40 meters at most.

According to the findings of the team led by Bristol University’s Ricardo Ramalho, published in 2 October issue of Science Advances, the mega tsunami was triggered by the catastrophic failure of a large chunk of a caldera on Fogo, a volcanic island in the Cape Verde Archipelago.

Rising 2829 meters from the sea level and 7 kilometers from the seafloor, Fogo is a volcanic island still showing signs of activity. In the 73,000-year-old event, close to a half of the volcano’s caldera became unstable and slipped into the sea. 

The tsunami, triggered by the sudden sinking of 160 cubic kilometers of rock ad earth, hit the Santiago Island lying opposite 55 kilometers away. 49 giant boulders, some the size of a refrigerator and some that of a bus, with diameters from 1 to 8 meters and weighing between 1 and 700 tons, were lifted by the wave of incredible energy atop a 220-meter-high plateau and were dragged 650 meters inland.

The wave also covered the slopes with 4-meter-thick sand deposits reaching up 100 meters.

Pointing to thousands of volcanic islands dotting the Pacific Ocean and rising numbers and populations of coastal metropoles, experts warn that threat of similar megatsunamis from similar failures or underwater landslides should not be underrated.

An example cited is a 1958 event in Alaska when an earthquake-triggered landslide into the Lituya Bay caused a tsunami which reached record 525 meters on the walls of the surrounding valley.

REFERENCES

  • 1. “Ancient tsunami heaved 700-ton boulders over island cliffs”, ScienceOnline, 2 October 2015
  • 2. “Hazard potential of volcanic flank collapses raised by new megatsunami evidence”, Science Advances, 2 October 2015
  • 3. http://advances.sciencemag.org/content/1/9/e1500456.full