Eastern Atlantic Tsunami

Tsunamis do not regularly strike Atlantic regions, with only about 10 percent of all tsunamis occurring in the Atlantic Ocean. A few tsunamis have been associated with earthquakes in the Caribbean region, such as in 1867 in the Virgin Islands, 1918 in Puerto Rico, and on June 6, 1692, when 3,000 people were killed by a tsunami that leveled Port Royal, Jamaica. The most destructive historical tsunami to hit the Atlantic region struck on November 1, 1755. Lisbon, Portugal, was the worst hit because it was near the epicenter of the earthquake that initiated the tsunami. At least three large waves, each ranging in height from 14 to 40 feet (4-12 m), struck Lisbon in quick succession, killing at least 60,000 people in Lisbon alone. England was hit by waves 6-10 feet (2-3 m) in height, and the tsunami even affected the Caribbean region, hitting Antigua with 12-foot (4 m) waves, and waves more than 20 and 15 feet (6 and 5 m) respectively in height swept Saba and St. Martin.

The Lisbon-Eastern Atlantic tsunami was generated by a large earthquake whose epicenter was located about 60 miles (100 km) southwest of Lisbon, probably on the boundary between the Euro pean and Azores-Gibraltar plates. The earthquake had an estimated magnitude of 9.0, and the shaking lasted for 10 minutes. During this time, three exceptionally large jolts occurred, causing massive destruction in Lisbon and the Moroccan towns of Fez and Mequinez. Most of Europe and Scandinavia reported seiche waves from lakes and inland water bodies.

The earthquake caused extensive damage in the city of Lisbon, toppling many buildings and causing widespread and uncontrolled fires in the city. In fear, many residents ran to the city docks in the harbor and on the Tagus River. As the buildings continued to collapse and the fire raged through the city, driving much of the population of 275,000 people to the waterfront, the worst part of this disaster was about to unfold. About 40-60 minutes after the massive earthquake, residents of Lisbon watched from the docks as the water rapidly drained out of the harbor, as if someone had pulled the plug in the bottom of a bathtub. A few minutes later a massive wall of water 50 feet (15 m) high swept up the harbor and over the docks, and then swept more than 10 miles (16 km) upriver. The tsunami was associated with a powerful backwash that dragged tens of thousands of people, bodies, and debris into the harbor. Two more giant waves rushed into the city an hour apart, and killed more of the terrified residents trapped between raging tsunami waves and a city crumbling under the forces of fire and earthquake aftershocks. About 60,000 people, nearly a quarter of the city's population, perished in the tsunami.

The November 1, 1755, earthquake caused extensive damage across the eastern Atlantic Ocean, with tsunamis sweeping the coasts of North Africa, Portugal, Spain, France, and the British Isles, and even islands in the Caribbean were affected. The tsunami moved inland by 1.5 miles (2.5 km) across low-lying areas of Portugal, and run-up heights around Portugal locally reached 65-100 feet (20-30 m) above sea level. Southern Portugal was the worst hit, where medieval fortresses and towns were destroyed or suffered heavy damage. The waves washed over the ancient walled city of Lagos, whose walls are anchored 36 feet (15 m) above sea level. The walls reduced the force of the waves, but the city was flooded, and the water had to drain out of the narrow city gates. The initial wave was followed by at least 18 secondary crests in southern Portugal, each adding damage upon the effects of the previous wave.

Western Europe was strongly hit by the tsunami as it spread northward. The south coast of England saw massive waves that tore up the coastal muds and sandbars, and the waves swept the shores of the Bay of Biscay. Boats in the North Sea were ripped from their moorings. The English Channel was swept by waves 10-13 feet (3-4 m) high at high tide, followed by even higher waves that oscillated every 10-20 minutes in the channel over the next five hours. The Azores, located offshore from Portugal, were hit by 50-foot (15-m) waves that raced across the Atlantic to the eastern seaboard of North America. Caribbean islands were hit by tsunamis with run-up heights in the range of 20-25 feet (6-7.5 m), with the worst hit areas reported to be St. Martin and Saba. Elsewhere in the Caribbean, 10-15-foot (3-4-m) waves were reported to have oscillated every five minutes for about three hours, affecting many harbor and coastal areas.

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