The rare tsunami that hit Brazil in 1755 – 09/21/2021 – Daily life

The eruption of the Cumbre Vieja volcano in La Palma in the Canary Islands (Spain) over the weekend has led many people to wonder if the event on the other side of the Atlantic Ocean could cause a tsunami in Brazil. Experts say the possibility of a tsunami is remote, but Brazil has registered a tsunami in the past.

One of the most recent studies, carried out in 2020 by the State University of Rio de Janeiro (Uerj), states that Brazil was already hit by a tsunami in 1755. Unlike the most well-known tsunamis, this tsunami would have been caused by the strong earthquake that shook Lisbon, in Portugal, that year, on the other side of the Atlantic Ocean.

The subject was discussed on the Brazilian Seismographic Network’s Twitter, with a video of José Alberto Vivas Veloso, retired professor from the Geosciences Institute and former head of the Seismological Observatory at UnB.

The 1755 earthquake was the largest ever recorded in Europe, with a magnitude of 8.7. It destroyed Lisbon, much of southern Spain and Morocco, and caused a massive tsunami that hit Ireland and the Caribbean. Estimates of victims vary due to the lack of records, but the smallest are between 20,000 and 30,000 deaths, while the largest speak of 100,000. The earthquake also ushered in a modern era in seismological studies.

The giant wave that formed with the earthquake in Lisbon crossed the Atlantic and caused damage to the Brazilian coast, says the work led by professor Francisco Dourado from the Center for Research and Studies on Disasters (Cepedes).

The research was based on a historical survey by professor Alberto Veloso, author of the book “Tremeu a Europa eo Brasil too”. The researchers from Dourado’s team carried out fieldwork along 270 kilometers and 22 beaches between Rio Grande do Norte and the south of Pernambuco.

“In the early afternoon of November 1, 1755, a tsunami hit the coast of the Northeast. It penetrated inland, destroyed modest homes and disappeared with two people. This is unknown to most Brazilians,” says Veloso.

There are reports in four letters of the time talking about the tsunami in Brazil. These letters were written by the archbishop of Bahia, by the governors of Pernambuco and Parayba and by a military man and are in the Overseas Historical Archive of Lisbon.

“The waters transcended their limits and made the inhabitants flee from the beaches”, says a letter of May 10, 1756, reporting the episode that took place on November 1 of the previous year in beaches in Paraíba.

Another letter reported by Veloso, dated March 4, 1756, says: “In Lucena and Tamandaré, the earthquake flood came inland about a league (4 to 5 km) inland and took some hut houses and one is missing. boy and woman.”

There are reports of rough seas also in Rio de Janeiro on the day of the Lisbon earthquake.

Brazilian and Portuguese researchers said they had collected traces of microanimals and chemical elements that could only have been brought to certain Brazilian beaches by large waves. The first step was to do a mathematical simulation of what the tsunami would have been like. Based on this simulation, the researchers went into the field.

On Pontinhas beach, in Paraíba, they identified a layer of thick sand that would have traces of the phenomenon.

According to the study by UERJ, in the region of Lucena beach, in Paraíba, the waves varied between 1.8 and 1.7 meters in height. In the region of Tamandaré, Pernambuco, waves reached between 1.9 and 1.8 meters, with a large volume of water.

The waves flooded up to 4 kilometers inland, mainly in places bathed by rivers and near the Ilha de Itamaracá (PE). In Tamandaré the flood was up to 800 meters, and in Lucena, 300 meters.

‘Minitsunami?’

In an article for Revista da USP in 2018, professor Veloso questions whether giant waves recorded in the past in Brazil could be considered “tsunamis”.

“Tsunamis are rare phenomena, but they can happen in any of the oceans, in several seas and in smaller portions of water bodies. They can have different origins, be large or small, disastrous or harmless. Such characteristics open up a wide range of opportunities, even to formulate the question: has a tsunami occurred, or could it happen, in Brazil? Perhaps it is not possible to answer such questions precisely”, writes Veloso.

The article states that the most common explanation for the absence of tsunamis in Brazil would be the lack of large-scale earthquakes at sea. But he says that the lack of records in the past is no guarantee that Brazil will not experience a tsunami, despite the remote possibility of this phenomenon being intense.

“The lack of knowledge of significant shocks in the past and the non-recording of strong earthquakes today do not ensure a similar situation for the future.”

His article focuses on five episodes of “unusual marine manifestations” on the Brazilian coast: in São Vicente (SP) in 1541, in Salvador in 1666, in Cananeia (SP) in 1789, in the Baía de Todos os Santos (BA) in 1919 and in the archipelago of São Pedro and São Paulo (off the coast of PE) in 2006.

In all these episodes, there were reports of violent seas or strong surf. But most of these phenomena were not even preceded by some kind of earthquake or volcanic eruption, which disfigures the occurrence as a tsunami. The large wave episodes in Cananeia and Baía de Todos os Santos had their origins in earthquakes — but with relatively low magnitudes.

“A tremor was identified that generated waves similar to a small tsunami. Despite being modest, the case is significant, as a Brazilian ‘minitsunami’ is being validated.”

Old Summit

Professor Velasco’s article also speculates on the possibility of a tsunami forming with the eruption of the Canary Islands’ Cumbre Vieja

“If, instead of the past, we go back to the future, we may face the threat of a possible megatsunami from the middle of the Atlantic Ocean. The warning came from British researchers and gained notoriety after the 2004 Indonesia tsunami (Ward & Day , 2001)”, he writes.

“The study suggests that during a new eruption of the Cumbre Vieja volcano, on Las Palmas Island, in the Canary Islands, off the west coast of Africa, one of its flanks would collapse towards the sea, causing a huge tsunami, mainly against the coast of the Americas . Depending on the volume of rocks involved in the landslide, somewhere between 150 km³ and 500 km³, huge waves with amplitudes of 15 to 20 m would reach the coast of the United States and also the northern coast of Brazil.”

But the professor claims that tsunamis caused by volcano eruptions are rare, and that there is little data on the Cumbre Vieja to speculate on the formation of a tsunami off the coast of Brazil.

“The article is controversial because of its unusual theme and because it involves unknown mechanisms, such as large lateral collapses on volcanic islands. Furthermore, the researchers emphasized the worst-case scenario by admitting the total collapse of the rock block, as it could come down, in parts, and the final impact would be much smaller. Another question is whether the tsunami would disperse quickly, or if it would spread to transoceanic distances, implying, in this case, great danger to coastal populations. Despite all the uncertainties of occurrence, a tsunami of this nature would produce damage throughout most of the Atlantic.”

The professor concludes: “There is no reason to fear, on our coast, the appearance of tsunamis with the magnitude and seismic mechanism similar to those that happened in Japan in 2011 or in Indonesia in 2004”.

The possibility of a new one was practically discarded by geologists from the Brazilian Seismographic Network, who published a post on the subject on their Facebook page.

The origin of this concern is a fact by American geologists about the possibility of a collapse of a part of the island (of La Palma) causing a tsunami in Brazil. Even that study considered that possibility remote.

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