Lisbon City, Portugal, Earthquake and Tsunami

On November 1, 1755, an earthquake of magnitude 9 hit Lisbon. Houses and shops in the lower part of the city, which had been built on unconsolidated ground, were completely wiped out and most of the parish churches were also destroyed. The shock of the day on which this happened was as strong as the event itself. November 1 is All Saints Day, a sacred occasion in a Catholic country like Portugal. In such a religious place the middle of the eighteenth century there were deeply held convictions about all the earth being an orderly creation guided by its Creator for the benefit of humanity. How could such a tragedy occur on All Saints Day and how could it happen when most people were in churches and where so many of them lost their lives? There was a sense of bewilderment all around. Those who were able to get out of buildings before they collapsed ran down toward the open areas near the sea, tragically unaware that a powerful tsunami was about to overwhelm the very area they thought was safe.

The city of Lisbon is a short distance inland from the Atlantic coast on the northern bank of the River Tagus. As people moved toward the mouth of the river close to the coast they noticed that the water’s edge had moved away from the land, leaving a broad stretch of beach covered with all kinds of sea life. What they were unaware of is that the withdrawal of water from beaches is frequently the first action of tsunamis as they reach shore. There is a pause as tsunamis encounter shallow water and friction is experienced by one part of the advancing wave. The wave stalls, then, like a suction pump, it withdraws all the water in front of it and recedes back out to sea, only to return later with much greater strength. There was no understanding of tsunamis 250 years ago so no one was prepared for the wall of water that subsequently crashed on to the shore destroying everything in its path. The wave was forty feet high at first and increased in height as it made its way up the valley of the River Tagus. The epicenter of the earthquake was located at sea about seventy miles southwest of Lisbon in a location where two tectonic plates meet, the Azores Plate and the Gibraltar Plate. Historically, those have frequently given rise to tsunamis, particularly if the quake’s magnitude is greater than 9. Thus, the result of the earthquake was first of all huge damage to Lisbon, but then lesser destruction up and down the coast as far south as North Africa and northwards to Britain and even Scandinavia. Along the French coast lakes and sea inlets were flooded. There were several phases to the tsunami. It was not just one wave that came in but rather a sequence over a period of time, so places continued to be hit at a distance over time. Lisbon was a city of 275,000 people in 1755 and first reports told of 20,000 buildings having been destroyed but this was just the beginning of troubles. As has so often happened in earthquakes fires break out and quite soon they are out of control. This was the case in Lisbon and the same thing happened more recently in San Francisco’s earthquake of 1906 and Tokyo’s of 1923.