October 31, 1542 Tsunami: Rio San Juan, Uruguay

Reference #14020 (unofficial translation):

The first historical record was written by Alvar Nunez Cabeza de Vaca (1555). A group of Spaniards leaving Buenos Aires and heading for Asuncion in 1542, on what would be the current coast of Colonia, in Uruguay, in the ravines near the mouth of the San Juan River (today's Estancia Presidencial Anchorena), experienced an earthquake and probably a seiche that caused the death of at least fourteen people.

After a failed attempt to refound Buenos Aires, following the evacuation of the city of Buenos Aires in 1541 (Schavelzon, 2006), Gonzalo de Mendoza made a second attempt in 1542 to refound the city. But the harsh winter made it difficult, so they decided to return to Asuncion. On the way, they anchored off the coast of Uruguay, at the mouth of the San Juan River, Colonia, with its coastal ravines.

On Saturday 31 October 1542, the eve of All Saints' Day, something disastrous happened to Captain Goncalo de Mendoca. He lost a ship loaded with goods and provisions and many people died. He writes that something strange happened while they were sailing. That day before, his ships were anchored on the river bank. Among them was a galley tied to a tree. He says that the earth shook, and the earth itself came down like a blow from the sea into the ravine. The trees fell into the river, and the ravine struck the brigantines, and the tree where the galley was tied gave such a blow to the galley that it pushed the ship upside down. And so it was dragged more than half a league (approximately two kilometres), with the mast underneath and the keel on top. In this event, fourteen people, including men and women, drowned in the galley and in the other boats.

It is difficult to estimate the magnitude of the earthquake from this information, but it is certainly the strongest earthquake ever recorded in the region.

And if it happened once, it is possible that one of similar magnitude could happen again. The fact that at least fourteen people died, in an open field, at a time when the region was virtually unpopulated, speaks to the significance of this event.

Reference #14019 (unofficial translation):

On the eve of All Saints' Day, when the ships were lying on the banks of the river near some high ravines, and the galley that Goncalo de Mendoca, the earth trembled and the earth itself came rolling down as if it were a sea blow to the ravine and the trees fell into the river and the ravine hit the gullies and the tree where the galley was moored gave such a great blow to the galley that it knocked it upside down. And so it carried her more than half a league, filling the mast below and the quinilla above, and this storm drowned in the galley and other vessels fourteen persons, men and women. And according to what those who were present said, it was the most fearful thing that ever happened. And with this labour they arrived at the city of the Ascension, where they were well provided for and supplied with all that was necessary. And the governor and all the people gave thanks to God for having brought them to safety and escaped from so many dangers as they had passed along that river.