An extraordinarily large tsunami 3800 years ago drove the people of northern Chile off the coast for many generations. A working group led by Diego Salazar from the Universidad de Chile in Santiago came to this conclusion based on geological traces of the monster wave, including mud and debris deposited far inland, typical signs of erosion and destroyed stone buildings. The team reports in “Science Advances” that these coincide with significant changes in the settlement pattern within the limits of measurement accuracy. Archaeological evidence shows that people settled further away from the coast in higher lying areas after the disaster. Based on the evidence, it estimates that the tsunami was triggered by an earthquake about as strong as the 1960 Valdivia earthquake in Chile, with a magnitude of 9.5. This caused tsunamis up to 25 meters high.
Behind the extreme tremors in Chile is the collision of two tectonic plates, as a result of which the seabed in front of the country submerges under the continent into the interior of the earth. These areas, called subduction zones, produce the strongest known earthquakes. The slowly advancing sea floor locks onto the edge of the continent and gradually compresses the earth’s crust until the contact zone breaks and snaps back. This movement displaces a lot of water and causes the tsunami waves – the larger the fracture zone, the stronger the earthquake. The experts assume that 3,800 years ago a 1,000-kilometer-long part of the subduction zone broke in one piece. This would make the rupture zone twice as long as that of the great Tohoku earthquake of 2011.
Around the time of the alleged tsunami, experts place the end of the cultural level known as “Archaic IV”, whose members lived as fishermen and foragers near the coast. From the next level, Archaic V, excavation teams found fewer dwellings, fewer artifacts, and fewer cemeteries. According to Salazar’s team, the distribution of the cemeteries indicates the lasting effect that the tsunami had on the population of the dry coastal plain. While these were between 10 and 25 meters above sea level before the quake, there are hardly any sites below 20 meters after the time in question.