On the morning of November 1, 1755, a great earthquake shook Portugal’s capital city of Lisbon as worshipers filled churches and cathedrals for the All Saints’ Day Mass.
In seconds it left the city in ruins and in minutes those ruins were on fire. The earthquake probably killed about 90,000 – 100,000 people. Many of the survivors fled to the wharves and keys of Lisbon’s port, but they would find no safety there.
The first tsunami wave surged up the Tagus estuary about an hour after the earthquake, reached a maximum runup of 12 meters (40 feet), and killed another 1000 people. At least two more tsunami waves surged into the city, completing the earthquake’s destruction.
At Portugal’s coastal city of Lagos the tsunami was even larger, perhaps 30 m (100 ft). It went on to damage the ports of Cadiz in Spain, then Safi and Agadir in Morocco.
The tsunami also spread north: it caused minor damage at Brest in Brittany, some flooding in England in the Scilly Islands and in Cornwall, and extensively flooded of the low-lying areas of the city of Cork, Ireland.
As it spread out across the Atlantic, the tsunami first reached Madeira, where observers recorded a runup of 4 m (13 ft), then the Canary Islands, the Azores, and eventually the West Indies, where observers recorded runups of about a 1 m (3 ft) in Barbados, Martinique, Guadeloupe, and Antigua (and questionable reports of large runup in the Virgin Islands).
Though the tsunami must have hit Colonial America, no one recorded it there, though it was observed in Newfoundland.
The model of this tsunami assumes its source was a magnitude 8.5 earthquake on the Horseshoe Fault off of Cape Finisterre. Baptista, et al. (2011) explain how this fault matches the tsunami observations better than the several other proposed sources for the Great Lisbon Earthquake.
Similitudes with La Palma?
As you know, the Cumbre Vieja volcano is currently erupting on the island of la Palma in the Canary Islands, which are even closer to the American East Coast.
As demonstrated in various scientific publications, a slide from this mountain could kill millions of people in Europe and along Northern America’s eastern seaboard. Some eminent scientists warn that it’s purely a matter of time until it happens.
And this is how the tsunami wave would propagate:
This is how the tsunami would develop:
- 2 Minutes: A 900 meters (3,000 ft) thick dome of water rises above the landslide.
- 5 Minutes: The dome collapses to a height of 500 meters (1,600 ft) as it advances by 50 kilometers (31 mi); additionally, wave valleys form.
- 10 Minutes: The landslide is now over. Waves reaching heights of 400–600 meters (1,300–2,000 ft) hit the three western Canary Islands.
- 15–60 Minutes: 50–100 meters (160–330 ft) high waves hit Africa. A 500 kilometers (310 mi) wide train of waves advances across the Atlantic.
- 3–6 Hours: The waves hit South America and Newfoundland, reaching heights of 15–20 meters (49–66 ft) and 10 meters (33 ft), respectively.
- Spain and England are partially protected by La Palma, thus tsunami waves there only reach 5–7 meters (16–23 ft).
- 9 Hours: Waves 20–25 meters (66–82 ft) approach Florida; they are not expected to grow farther as they hit the coast.
Even if you don’t believe the tsunami scenario will ever happen, just prepare yourself for the worse… Then you will feel safer!