(ORDO NEWS) — A giant earthquake that triggered a tsunami that hit northern Chile 3,800 years ago damaged coastal communities so much that it took people 1,000 years to get back to shore, scientists say.
The ancient super-quake had a magnitude of about 9.5 and was so powerful that it triggered a tsunami that threw boulders hundreds of meters deep into New Zealand, thousands of miles away and across the ocean.
The discovery is evidenced by uplifted land structures (so-called littoral deposits) and samples of marine rocks, shells and marine life washed up by tsunami waves far ashore, into the higher reaches of the Chilean Atacama Desert.
This serves as a grim warning about the destructive potential of large tsunamigenic earthquakes, which may have previously escaped our notice.
“We found evidence of marine sediments and many animals that lived quietly in the sea before being washed up on land,” says geologist and tsunami specialist James Goff of the University of New South Wales, Australia.
“And we found all this very high and far inland, so they couldn’t have been brought there by a storm.”
A research team led by anthropologist Diego Salazar of the University of Chile has been conducting research for several years in the Atacama Desert, which is particularly vulnerable to megathrust earthquakes due to its proximity to the convergence of the Nazca and South American tectonic plates, with the first plate subducting under the second.
It was this phenomenon and its seismic response that led to the most powerful earthquake in history, the 1960 Valdivia earthquake in southern Chile; thousands of years earlier, it seems that the same tectonic stresses led to an equally diabolical, but undocumented, predecessor in the north of the country.
“It used to be thought that an event of this magnitude couldn’t happen in the north of the country simply because there couldn’t be a long enough gap,” says Goff.
“But now we’ve found evidence of a 1,000-kilometer-long rip just off the coast of the Atacama Desert, and it’s a massive event.”
In their research, the scientists used radiocarbon dating to get an idea of the age of intertidal deposits that stretch 600 kilometers (about 370 miles) of Chile’s coastline.
Readings from several deposits point to the existence of “a tectonic event that could have uplifted intertidal deposits throughout the study region, triggered paleotsunamis, and triggered social upheavals on a regional scale,” the researchers write in their paper.
At the time of this event, the people living in this part of the world were hunter-gatherer communities. Archaeological finds indicate that the tsunami wave that arose as a result of the earthquake overturned their stone buildings – and not once, but twice, with a strong reverse flow of the tsunami, flowing back into the sea, wreaking havoc.
The consequences for all the people who were lucky enough to survive the immediate disaster were long-term: according to reports, this area remained uninhabited for 1000 years, although people lived on this stretch of coast for almost 10 thousand years before the crisis.
“The local population was left with nothing,” says Goff. “Our archaeological work has shown that a huge social upheaval followed as communities moved inland beyond the reach of the tsunami.”
Over time, and with dozens of generations, the courage (or perhaps forgetfulness) of the locals increased, and people eventually returned to the ocean after about 1000 years.
“Abandonment of previously occupied territories and changes in patterns of mobility and spatial arrangement of settlements and cemeteries were likely resilience strategies developed by hunter-gatherer societies,” the researchers write.
“However, knowledge of these giant events and their consequences appears to be waning over time.”
In addition to filling gaps in our historical understanding of this giant event – an earthquake as powerful as any known to mankind – the study is a cautionary tale about future risks from similarly powerful megathrust earthquakes, the researchers say.
“While this earthquake had a big impact on people in Chile, the South Pacific islands were uninhabited when the tsunami hit them 3,800 years ago,” says Goff.
“But now they are all well populated and many of them are popular tourist destinations, so the next time something like this happens, the consequences could be disastrous if we don’t learn from these findings.”
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