3,800 years ago, a magnitude 9.5 earthquake would have triggered a devastating mega-tsunami on the Chilean coasts. Prehistoric populations would have taken refuge inland and preserved the memory of this catastrophe for almost 1,000 years.
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[EN VIDÉO] Kézako: The mysteries of how tsunamis form Tsunamis are among the most devastating natural disasters. These waves, which are up to 30 meters high, hit the coast with unstoppable force. With the Kézako programme, Unisciel and the University of Lille 1 are revealing to us the mysteries of the origins of this phenomenon.
The west coast of South America faces significant seismic risk due to its location on the boundary of converging plates. Each year, the subduction that causes the Nazca oceanic plate to collapse beneath the South American tectonic plate is actually responsible for many earthquakes, some of which can be very powerful. The strongest earthquake in modern times was recorded off the coast of Chile in 1960. With an estimated magnitude of Mw 9.5, this earthquake raised the sea floor by six meters in places and caused a powerful tsunami. Waves 10 to 12 meters high swept over the coast of Chile, sweeping away everything in their path and killing 3,000 to 6,000 people.
A tsunami would certainly be very deadly for the prehistoric populations living along the coast
However, this tectonic context is not new and has notably given birth to the Andean chain. It is therefore likely that such seismic events of more or less similar amplitude have already occurred in the past. A team of researchers also provides evidence that a mega-tsunami struck the Chilean coast about 3,800 years ago. The results of the study, published in Science Advances, suggest that the magnitude of the earthquake at the origin of this tsunami must have been similar to that seen in 1960. However, by that time Chile was already populated by populations of hunter-gatherers and fishermen living along the coast. A highly endangered situation in the event of a tsunami. Scientists also show that after this catastrophic event, the population would have left the coast to settle inland. This situation would have lasted approximately 1,000 years, suggesting a very long-term transmission of history with significant resilience.
To reach these conclusions, scientists conducted geological and archaeological excavations in the Atacama Desert. Geological research focused on the sedimentary deposits left behind by the tsunami. Dating of shells and fragments of charcoal made it possible to fix this event around the year -1778. The location of the deposits and the numerical modeling of the tsunami made it possible to estimate the magnitude of the earthquake at Mw 9.5. This would have created a devastating wave 15 to 20 meters high. It is easy to imagine the devastating effects this tsunami had on the coastal residents. Signs of destruction have also been observed at several coastal archaeological sites.
The memory of the catastrophe has been passed on for almost 1,000 years
This event marks a major turning point in the organization of prehistoric societies living in this region, including a massive inland or higher elevation shift. The most impressive result is that these populations would not have returned to shore for 1,000 years. This observation shows that the memory of the tsunami was passed from generation to generation for almost a millennium. We also observe that population resettlement has been much more cautious in the long term, with the development of residential areas further from the coast or on the reliefs, at least 20 meters above sea level which, surprisingly, corresponds to the limit of the tsunami that occurred 1,000 years earlier. In what form was this reminder of the danger conveyed? Scientists don’t know. It is certainly an oral history as these societies do not yet have a written language.
These results allow a better understanding of the evolution of the population in this region of the world and their ability to adapt and resilience in the face of a natural disaster of this type. They should also allow to better define the risk to which today’s heavily populated Chilean coasts are exposed.
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