Few people know that Lake Nahuel Huapi experienced a freshwater tsunami in 1960. This is an extremely rare phenomenon, and it had some nasty consequences on the coastline and the city and port of San Carlos de Bariloche.
Valdivia earthquake of 1960
The "1960 Valdivia Earthquake" or "Great Chilean Earthquake" was the largest earthquake ever recorded: its magnitude was 9.5 to 9.6.
It took place on May 22, 1960, and killed between 1000 and 6000 people, and provoked tsunamis that rushed across the Pacific Ocean and struck New Zealand, Australia, Hawaii, the Aleutian Islands and Northwestern Asia. The tsunami also battered the coast of Chile, and the tremor caused a tsunami in Lake Nahuel Huapi.
The Lake Tsunami
Those on the lake's shores saw the water recede from the beaches and return as a wave front that was 5 m (16 ft.) high. It razed the local port and killed two people.
A paper published in 2009 analyzed the lake tsunami, and why the port was razed (Villarosa, G., Outes, V. ., Gomez, E. A., Chapron, E., & Ariztegui, D. . (2009). Origen del tsunami de mayo de 1960 en el lago Nahuel Huapi, Patagonia: aplicación de técnicas batimétricas y sísmicas de alta resolución. Revista De La Asociación Geológica Argentina, 65(3), 593-597. Retrieved from https://revista.geologica.org.ar/raga/article/view/891).
The authors concluded, after analyzing the lake bed by the port, that "The impact of the seismic waves produced huge mass-failure below 70-80 m water depth. Thefailure was probably induced by the presence of a non-cohesive surface (tephra layer?) that acted as a sliding surface, and the mobilized material evolved into a mega turbidite in the deep basin. A large volume of water was displaced by the mobilization ofthese sediments producing a tsunami that hit the coasts of Bariloche and destroyed the harbor of the city."
It was a period of activity along the edge of the tectonic plates in Southern South America, the Nazca Plate subducts beneath the South American Plate and provokes earthquakes and volcanic activity along a line running beneath the Andes. The first quake shook Concepción (Chile) on May 21st. with an 8.1 magnitude. The next day two new quakes (7.8 and 7.1 magnitude) hit Concepción again, followed by the record-breaking 9.5 quake of Valdivia. It triggered the eruption of the Puyehue-Cordón Caulle volcano on May 24th which spewed ashes on Lake Nahuel Huapi and the City of Bariloche. Below is a view of the eruption.
Bariloche Port
The port of San Carlos was originally built in the 1930s and consisted of a timber pier (Pictured below in 1937).
The port was enlarged with an enclosure along its northern side as can be seen in the picture below from the early 1950s.
It was damaged by a fire in 1958 and rebuilt. Then the tsunami destroyed it. Below are some pictures taken after the tsunami. Some ships in the port survived, others sank.
The tourist ships that visited Victoria Island, Puerto Blest and the Arrayán forest on Quetrihue Peninsula, moved their operations to the port of Llao Llao, Puerto Pañuelo port. It took decades for a new port to be built on the site of the old one. The port modern can be seen below.
There have been other tsunamis in the past
Geologic sampling of the sediments in the lakes Moreno, El Trébol, and Escondido, on the southern side of Lake Nahuel Huapi, (see the Thesis - Eventos paleoambientales en la cuenca del Lago Nahuel Huapi registrados en testigos sedimentarios lacustres durante los últimos 19.000 años, Lirio, Juan Manuel) found that the Nahuel Huapi paleolake (known as Lake Elpalafquen) had a higher water level than the current lake. It was closed in on its eastern tip by the terminal moraines of the glaciers that occupied the lake's basin during the last Ice Ages. The paleolake levels fell in three different stages, from 45 m to 17.5 m, and 6 m above the current water levels. These drops were associated with seismic-volcanic events recorded in the sediment cores analyzed by the authors:
"The erosional unconformities identified in the sedimentary cores are covered by tephra layers several centimeters thick, suggesting the existence of seismic events prior to the tephra collapse, similar to those recorded during the Valdivia earthquake on Lake Nahuel Huapi."
- 19,081 ± 0,274 ky cal BP the water of the paleolake stood 47 m higher than its current, reaching 815 m above sea level.
- The first descent took place 16,840 ± 0,250 ky cal BP.
- Another event 16,381 ± 0,269 ky cal BP also impacted on lake levels cutting off the basin of Lake Guillelmo and Lake Mascardi from the Nahuel Huapi basin, as it modified the marsh that separates Mascardi from Lake Gutierrez, leading the former to drain towards the Pacific Ocean (through the Manso and Puelo rivers), and shifting the continental watershed eastwards.
- 15,537 ± 0,249 ky cal BP the lake level dropped to 17.5 m above its present level.
- Followed by another decrease 14,680 ± 0,261 ky cal BP that left it 6 m above the current lake level.
- 1,750 years BP the lake dropped to its current level of 768 m above sea level.
These eartquake-induced lake level fluctuations were catastrophic events. The author writes: "It is possible that several of them would have catastrophic characteristics for the Limay River basin, dumping a large volume of water in a very short time; e.g., the author estimated that a 10-m drop in the Nahuel Huapi Lake basin would contribute a volume of 6.2 km3 of water to the Limay River."
A massive downstream flood.
So the gradual breakage of the eastern terminal moraine due to quakes led to a lower lake level, and erosion of the moraine between these events reduced the level even further. Notice how in the past, lakes Espejo and Corentoso (top left and right), and Gutierrez, Mascardi and Guglielmo (bottom center) were all linked as long arms to the main body which nowadays is Lake Nahuel Huapi.
These events would have had an impact on any potential cryptid living in the lake's basin.
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