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A mega tsunami taller than a 50 - level skyscraper once engulfed an island off the west coast of Africa , research worker say .
This determination intimate the giant landslides and killer waves that such tsunami can trigger might dumbfound a major hazard to masses living on islands and coasts , scientists add .
A researcher chisels out a rock sample for dating. Scientists have found evidence that a tsunami triggered by a volcanic collapse swept huge boulders like this one into the highlands of the island of Santiago.
Tsunamis are monster wavesthat are often due to seism . The2004 Banda Aceh earthquake and tsunamikilled about 250,000 hoi polloi , whilethe 2011 Tohoku earthquake and tsunamithat fall upon offshore of Japan killed about 20,000 mass and triggereda nuclear cataclysm .
Not all tsunami are make by seism . Some of these giant waves are due to landslide , for instance , those occur insubmarine canyonsor on the flanks of volcanoes . For example , in 1792 , part of Japan ’s Mount Unzen crock up , resulting in waves as gamey as 300 foot ( 90 meters ) that killed about 15,000 people . In 1958 , an quake sent a landslide into Alaska ’s isolate Lituya Bay , engender a titanic wave 1,724 feet high ( 525 one thousand ) , the largest ever recorded . Two fishermen who chance to be in their gravy boat that 24-hour interval were carried over a nearby forest . Miraculously , they survived . [ 10 Tsunamis That change History ]
However , scientist were uncertain how much wrong tsunamis that are trigger by volcanic collapses might cause in the open sea . All the elephantine waves triggered by volcanic collapses in the retiring few hundred eld occurred in restrain space that concentrate the zip of such collapses into small volumes of water supply . In contrast , in the unfastened ocean , late enquiry intimate that wave engender by landslides loosely lose DOE rapidly .
Now scientists have receive grounds that a sudden vent collapse trigger a giant tsunami dwarf anything in recorded history that traveled 12 of mil .
" These finds provide another line of evidence that volcanic flank collapses really can happen suddenly and catastrophically and trigger giant tsunamis , and so we should not underestimate the peril electric potential of these effect — that is , the threat they pose to our society , " study jumper cable author Ricardo Ramalho , a geologist at University of Bristol in England , told Live Science .
Oddball boulders
The researcher concentrate on Santiago , the largest of the Cape Verde Islands off the west coast of Africa . Santiago , which is home to about 250,000 people , lies about 34 miles ( 55 kilometers ) from Fogo , one of the world ’s largest and most fighting island volcano .
Currently , Fogo stands about 9,300 metrical unit ( 2,830 m ) above ocean level . It erupts about once every 20 old age , most latterly last fall , when its lava flow displaced more or less 1,200 people and destroyed several building , including a novel volcano visitors ' center .
Ramalho and his colleagues were transmit research on Santiago when they discovered unusual boulders dwell as far as 2,000 metrical foot ( 610 m ) inland and nearly 650 feet ( 200 megabyte ) above sea level . Some boulders were up to around 25 feet ( 8 m ) wide and weigh up to 770 piles ( 700 metrical slews ) . [ See Photos of the World ’s Weirdest Balancing Rocks ]
These gargantuan rocks differ completely from the volcanic terrain on which they lie down . Instead , they agree limestone and other rocks that ring the island ’s shoreline .
" At first , we were quite nonplussed by what we found in the field — why were such large boulders stranded on the landscape painting ? " Ramalho said . " We got really excited when we realized that the only way to explain the stemma of those bowlder was with a massive tsunami impact . "
Computer models avail the researchers calculate the size of the wafture that must have thrust these giant rock onto Santiago .
" We judge that the wave was possibly about 170 meter ( 557 feet ) high upon comer to Santiago ’s coastline , " Ramalho said .
In comparison , the largest known late tsunamis , which ravage the Indian Ocean ’s coasts in 2004 and eastern Japan in 2011 , reached only about 100 feet ( 30 m ) in height . " When you empty the implications of discovery like these , you naturally feel humble by the exponent of nature , " Ramalho said .
The mega tsunami
To date when thismega tsunamihappened , Ramalho and his colleagues analyzedisotopes of heliumembedded in the boulders . ( Isotopes are particle of an element with depart numbers of neutron . ) The isotopes that are present in a boulder change depending on how long the rock has been lying out in the open , exposed to cosmic rays from outer space . Their findings intimate this event happened about 73,000 year ago , when a landslide on Fogo may have send up to 38 cubic miles ( 160 cubic klick ) of rock crashing into the sea .
Other scientists have take that Spain ’s La Palma Island could generate mega tsunamis as well . Tsunami researcher Simon Day at University College London and his confrere have polemically suggested that if La Palma ’s active Cumbre Vieja volcano erupted , a landslide on its westerly flank might trigger a wave about 2,950 groundwork ( 900 m ) high . They argued this mega tsunami would devastate nearby island , and still be about 330 feet ( 100 m ) eminent when it arrive at the western seashore of Africa and about 165 feet ( 50 m ) in high spirits when it run into Florida and the Caribbean .
" I would say that if there was a large - enough ruinous landslip , tsunamis with an initial magnitude of 3,000 feet ( 915 m ) would be potential , " Ramalho pronounce . " But I do n’t know the geology of La Palma , and so I can not remark on the validity of Simon Day ’s assumptions . "
anterior inquiry had raised doubts over whether large volcanoes were capable of suddenly expend as much careen into the ocean as these novel findings hint . " Our finds imply that flank collapse can indeed happen catastrophically and generate giant tsunami , " Ramalho said .
However , Ramalho accentuate that volcanic prostration do not always happen catastrophically and do not always generate mega tsunamis .
" Our work shows that we need to be argus-eyed and that we should not underestimate the terror posed by wing collapses and the tsunamis they trigger , but our work does n’t incriminate that a wing [ collapse ] is about to happen on Fogo or anywhere else , " Ramalho say . " Each volcano take to be monitored and analyzed separately and in detail . "
Ramalho and his colleague plan to look into whether Fogo or other volcanoes might collapse and trigger jumbo tsunamis in the time to come . " There is a growing awareness that utmost geohazards such as these will eventually , one solar day materialise , so we might as well coolly and realistically see what can be done to mitigate their effects , " Ramalho said .
The scientists detail their finding online Oct. 2 in the daybook Science Advances .
