On this day, December 16th, in the year 1575, an earthquake occurred near Valdivia Chile. The city of Valdivia and the Chiloé Archipelago were once the two southernmost outliers of the Spanish Empire, located just north of the southern tip of South America. The earthquake occurred at 2:30pm, local time, and it is estimated that it was a magnitude 8.5 on the surface-wave scale and estimated magnitude of 9.0 on moment magnitude. The earthquake triggered the flooding of Valdivia. My first thought was, exactly how do we know all this. The answer is that Pedro Mariño de Lobera, who was the governor of Valdivia at that time, reported the quake and that the waters of the river opened like the Red Sea, one flowing upstream and the other downstream. That must have been quite a sight, and not likely to be one people would forget, and clear written documentation from an eyewitness helped too. 
Acting quickly, Mariño de Lobera evacuated the city because he was concerned about the dam at Laguna de Anigua (now known as Riñihue Lake). The dam, he suspected, would not hold up to the pressure any cracks might place on it. Then, suddenly, the dam gave way, and while he noted the unfortunate deaths of many Indigenous people, no Spaniards died, because the settlement of Valdivia was temporarily relocated away from the riverside. I’m sure that like many people these days who think that they can ride out a hurricane, flash flood, or other such natural disaster; there were those who did not see evacuation as necessary. They evacuated anyway, and I’m sure they were glad they did.
I have often wondered how we can possibly know that on that day, in 1575, an earthquake occurred, and where. I suppose if I were a seismologist, I might have a better understanding of how all that works, and how we could have evidence of something so long ago…much less the magnitude of it. Nevertheless, apparently, they know a lot about it…and they were able to determine that the effects of this earthquake are comparable to those of the 1960 Valdivia earthquake, which at 9.4 to 9.6, was the largest quake ever recorded on Earth. That quake also caused subsequent Riñihuazo flooding. That was significant to the seismologists, who learned that these similarities indicate that large earthquakes exhibit patterns that span several centuries. Today, Valdivia has made a recovery from both earthquakes. The 2017 census lists the population at over 150,000.
Leave a Reply