Volcanic eruptions often produce a overplus of jeopardy that human race have to deal with , from the annihilative , sear pyroclastic flows of volcanoes likeMount St Helensto the near - unstoppable lava flows ofMount Etna . Some are more unpredictable than others , and a new study published inScience Advancesdescribes perhaps the least understood and most unpredictable of them all : a volcanically - induce megatsunami .
work in theCape Verde Islands , geologists have found striking grounds point that the flop of a wing of the pelagic volcano Fogo into the ocean 73,000 years ago triggered a so - anticipate megatsunami that at one spot exceeded elevation of 270 meters ( 886 feet ) – approximately the same height as the Chrysler Building in New York City . Crashing into the nearby island of Santiago at upper of up to 120 meters ( 395 foot ) per second , it cast aside lots of dense , declamatory block of rock onto the island .
This tsunami would have been nothing like man have ever observed . For comparison , the 2011 earthquake - induced tsunami that impacted the eastern seaside of Japan , which pop nigh 16,000 people , was a bare 39 meters ( 127 feet ) in altitude . A Fogo - style megatsunami impact a population - dense region would make an untold number of casualties dwarfing that of the 2011 Nipponese tsunami .
The study , led by volcanologistDr Ricardo Ramalho , describe a serial of unusual boulders on mainland Santiago . Geologically unlike the young volcanic terrain they were pick out on , up to 600 meters ( 2,000 feet ) inland and up to 200 meters ( 650 understructure ) above ocean level , these more marine - character rocks resembled those found on the shoreline . Sometimes weighing up to 700,000 kilograms ( 1.5 million punt ) , the most plausible account is that a colossal wave ripped them up from the shoreline and threw them far inland . The dimensions of this wafture were calculated by determining the Energy Department required to deposit these boulder in the first place .
Unlike normal tsunamis , which are triggered by underwater temblor run a great mass of water system , megatsunamis are yield when an extremely large bulk of stuff suddenly give way into a lake , sea or sea . Their pinnacle wave height is far higher than that of average tsunamis , and they are often cause by asteroid impact or volcanic flank collapses touch off by eruptions or consort seismic activity .
As it turns out , a nearby volcano has a rather goodish scar : the easterly wing of the island of Fogo , reside 55 kilometers ( 34 sea mile ) to the west of Santiago , is missing . Radiogenic date techniques placed the deposition of the boulders on Santiago at around 73,000 years years ago , just about matching that of the wing flop , date by aseparate studyto have occurred between 123,000 and 62,000 age ago . Up to 160 cubic kilometers ( 38 cubic miles ) of rock , trigged by violent volcanic activity at Fogo , collapsed into the sea all at once , squeeze a immense amount of pelagic water to rush eastwards towards Santiago at unbelievable speeding .
Megatsunamis are not just raw phenomenon consigned to ancient history . A far more recent historical megatsunami event occurred in 1792 , when magma ram its way of life up towards the vent ofMount Unzenin Japan bring forth violent temblor that trip the collapse of the southerly wing of the volcano . The ensue megatsunami kill more than 15,000 people .
As for how frequent such event are , volcanologists are uncertain . " Based on the geologic record book from Hawaii and the Canary islands , people have estimated that large wing collapse happen there at least once every 100,000 year – but I do n’t sleep together how solid this estimate is , " Dr Ramalho told IFLScience . " We still do n’t have solid constraints on the relative frequency of such events . "
