On the morning of November 1, 1755, a great earthquake shook Portugals 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 30,000 people, though some estimates double that figure. Many of the survivors fled to the wharves and keys of Lisbons 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 earthquakes destruction. At Portugals 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. Our 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. Reference: Baptista, M.A., Miranda, J.M., Omira, R., & Antunes, C. (2011). Potential inundation of Lisbon downtown by a 1755-like tsunami. Natural Hazards and Earth System Science, 11(12), 3319--3326.
Posted on: Sat, 08 Feb 2014 20:17:08 +0000