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The 1755 Lisbon Earthquake
The Portuguese capital was flattened by a massive earthquake in 1755. Some historians say its after effects were far more profound than leaving city in rubble.
National Geographic tells us that “In plate tectonics, Earth’s outermost layer, or lithosphere—made up of the crust and upper mantle—is broken into large rocky plates.” These plates float on partially molten rock and are constantly moving, in some cases as much as six inches (15 centimetres) a year.
The problem is that the plates bump into each other and, when this happens, the result is earthquakes. There are about 20 plates and one of the biggest is the African Plate.
This plate covers most of the African continent and stretches roughly halfway across the Atlantic Ocean. At its northwestern edge it meets the Eurasian Plate and the junction is called Azores–Gibraltar Transform Fault. This is a fracture that stretches from Gibraltar in the east out into the Atlantic at the Azores.
The African Plate is moving northeast at a rate of about 0.85 inches (2.1 cm) a year. The Eurasian and African Plates are sliding past each other. In a perfect world, the two plates would pass with ease, but this isn't a perfect world.
Sometimes, it's more accurate to say the plates grind past each other and then the worst thing might happen—they get stuck.
However, the two land masses behind the point of contact don't stop moving so the pressure builds up massively until the two sides snap apart creating an earthquake. That's what happened deep under the Atlantic Ocean 120 miles (200 km) southwest of Portugal's Cape St. Vincent in 1755.
All Saints' Day Earthquake
It was about 9:30 in the morning on November 1st in Lisbon, when the earthquake hit about 180 miles (290 km) away. Seismologists today estimate the quake measured 8.5 or more on the Richter Scale, making it a very big one.
The force released has been estimated to be the equivalent of 32,000 Hiroshima bombs, and tremors were felt as far away as Switzerland.
It was All Saints' Day, and the pious had packed the churches of Lisbon to celebrate the holy feast. As the congregants knelt in prayer they felt the first tremors, followed by the big one. It lasted between three-and-a-half and six minutes and must have filled the people with absolute terror.
Masonry started falling from the roofs of medieval churches that were not built to withstand such massive shaking. Lighted candles set fire to fabrics and vestments, and soon, it seemed, the entire city was on fire. A firestorm developed that sucked up all the oxygen, suffocating people.
To avoid the flames and crumbling buildings, people fled to the waterfront. This proved to be a poor strategy. Forty-five minutes after the quake, the tsunami hit. The first wave is estimated to have been almost 30 feet (nine metres) high. Those on the docks were drowned as were hundreds of other people in low-lying areas. About 85 percent of the city was destroyed.
University of Liverpool, England geographer David K. Chester estimates the death toll in Lisbon and surrounding area to have been in the region of 100,000 people. He adds that “the Lisbon earthquake of 1755 is probably the greatest seismic disaster to have struck western Europe.”
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Faith Is Shaken
At the time, natural disasters such as earthquakes were thought to be the work of God, as a punishment for sinfulness. But, the people were marking one of the holiest days in the liturgical calendar. Why would God chastise us so cruelly on such an important religious day, they asked? Some of the great minds of the time had an answer.
News of the massive quake spread across Europe and prompted many to suggest that God had nothing to do with such catastrophes. Maybe, God was not omnipotent.
Philosophers and other intellectuals who were influential in what we now call the Age of Enlightenment suggested that some agency other than God caused the Lisbon earthquake. In particular, Voltaire, who witnessed the event, in his novella Candide, suggested there was a scientific reason for such natural phenomena.
The Marquis of Pombal was handed the job of rebuilding the city. He was an advisor to King Joseph I of Portugal, and an Enlightenment scholar. He believed there was a rational and scientific explanation for the disaster that hit the city. This brought him into conflict with Jesuits who were preaching that it was the sins of the people that caused the earthquake.
When the Jesuits were implicated in a plot to assassinate the king they were banished from Portugal.
The religious order had formed the backbone of the education system in the country. Pombal used the earthquake to leverage a redesign of the schools and universities to be modelled on the ideas of the Enlightenment. In so doing, he dragged Portugal out of the suffocation of medieval superstition and into the age of reason.
Under the instructions of the Marquis of Pombal, Lisbon was rebuilt using engineering principles to minimize the damage from future earthquakes. He is also credited with starting the new scientific discipline of seismology, as well as disaster planning. His ideas were picked up and used elsewhere in the Western world.
But, there is concern that the lessons learned in 1755 have since been unlearned.
Here's Laura Trethewey, writing for Hakai Magazine: “As the city has grown, the riverfront expanded with the help of infilled sediment. During an earthquake, this unstable land will churn into liquid morass. According to [geophysicist Maria Ana] Baptista and other researchers, Portugal’s tourist industry is to blame for stymieing disaster warning and preparation because it’s fearful of losing visitors and income. 'We don’t have evacuation routes in Lisbon. We don’t have tsunami signs,' she says. 'The tourism industry is only just starting to understand the importance of being prepared.' ”
- In 1777, Queen Maria I ascended to the throne of Portugal. She was close to the Jesuits and hated the Marquis of Pombal with a passion. She removed him from all his government responsibilities. He retired to a palace he had built and died peacefully in 1782 at the age of 82.
- Lisbon was no stranger to earthquakes. In the 14th century, there were at least two major events. In 1351, a magnitude 7.7 quake hit east of the city and resulted in a death toll estimated at 30,000. In 1969, an earthquake to the south, in the Gulf of Cadiz, caused deaths in Portugal, Spain, and Morocco.
- “Plate Tectonics.” National Geographic, undated.
- “The 1755 Lisbon Earthquake.” David K. Chester, Progress in Physical Geography: Earth and Environment, September 1, 2001.
- “The Lisbon Earthquake of 1755.” lisbonlisboaportugal.com, undated.
- “The 1755 Lisbon Earthquake: Marquis Pombal Uses Science to Rebuild.” Stories in Science, undated.
- “The Earthquake That Brought Enlightenment.” Laura Trethewey, Hakai Magazine, September 1, 2020.
- “The Earthquake That Changed the Course of History.” BBC Reel, undated.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2022 Rupert Taylor