Mega tsunami was 270 meters high
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 the volcano’s
caldera became unstable and slipped into the sea.
The tsunami, triggered by the sudden sinking of 160 cubic kilometes 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 220meter-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 and rising
numbers and
populations of ccoastal metropoles, experts warn that threat of similar megatsunamis from similar
failures or underwater landslides should not be underrated.
An example cited is a 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
Raşit Gürdilek
REFERENCES:
“Ancient tsunami heaved 700-ton boulders over island cliffs”, ScienceOnline, 2 October 2015
“Hazard potential of volcanic flank collapses raised by new megatsunami evidence”, Science
Advances, 2 October 2015
http://advances.sciencemag.org/content/1/9/e1500456.full