Immediately after the earthquake, many inhabitants of Lisbon looked for safety on the sea by boarding ships moored on the river. But about 30 minutes after the quake, a large wave swamped the area near Bugie Tower on the mouth of the Tagus. The area between Junqueria and Alcantara in the western part of the city was the most heavily damaged by the wave, but further destruction occurred upstream. The Cais de Pedra at Rerreiro do Paco and part of the nearby custom house were flattened.
A total of three waves struck the shore, each dragging people and debris out to sea and leaving exposed large stretches of the river bottom. In front of the Terreiro do Paco, the maximum height of the waves was estimated at 10 meters. Boats overcrowded with refugees capsized and sank. In the town of Cascais, some 30 km west of Lisbon, the waves wrecked several boats and when the water withdrew, large stretches of sea bottom were left uncovered. In coastal areas such as Peniche, situated about 80 km north of Lisbon, many people were killed by the tsunami. In Setubal, 30 km south of Lisbon, the water reached the first floor of buildings.
The destruction was greatest in Algarve, southern Portugal, where the tsunami dismantled some coastal fortresses and, in the lower levels, razed houses. In some places the waves crested at more than 30 m. Almost all the coastal towns and villages of Algarve were heavily damaged, except Faro, which was protected by sandy banks. In Lagos, the waves reached the top of the city walls. For the coastal regions, the destructive effects of the tsunami were more disastrous than those of the earthquake.
In southwestern Spain, the tsunami caused damage to Cadiz and Huelva, and the waves penetrated the Guadalquivir River, reaching Seville. In Gibraltar, the sea rose suddenly by about two meters. In Ceuta the tsunami was strong, but in the Mediterranean Sea, it decreased rapidly. On the other hand, it caused great damage and casualties to the western coast of Morocco, from Tangier, where the waves reached the walled fortifications of the town, to Agadir, where the waters passed over the walls, killing many.
The tsunami reached, with less intensity, the coast of France, Great Britain, Ireland, Belgium and Holland. In Madeira and in the Azores islands damage was extensive and many ships were in danger of being wrecked. The tsunami crossed the Atlantic Ocean, reaching the Antilles in the afternoon. Reports from Antigua, Martinique, and Barbados note that the sea first rose more than a meter, followed by large waves.
The earthquake struck first in the South Atlantic Ocean generating one of the worst tsunamis in European history. Run-up reached as high as 35 meters (well over 100 feet).
The waves reach their highest point where they strike low-lying areas directly. They reach farthest inland in the drainage valleys that lie perpendicular to the most advanced point of the wave, itself. It is not safe to return to low-lying costal areas immediately after the leading wave has struck because of secondary waves and the possibility of rebound-ing waves bouncing off of some landmass and returning to the original landfall.
The leading wave may not be the most dangerous because of less debris than might be contained in the following waves PLUS the possible cumulative effect of the combination of the amplitudes of subsequent and rebounding waves. Tides are another consideration should the tsunami wave occur at high tide, simultaneously, upon reaching landfall.
Tide gauges are devices used to record changes in sea level at coastal locations. Normal tides would create a regular, gently changing record of the water level. If one watches the leading wave and the tide gauge, one should be able to see the "arrival signature" of the leading wave on the tide gauge readout. Some wells in the area were completely devoid of water from the "out-surge" or type of "rip-tide" of ground water from local and coastal wells.
Often, the speed of the tsunami wave is so great that a 5-minute warning is all that can be expected which is insufficient time for any reasonable escape or evacuation. Lisbon had no more than 30 minutes after the quake and before the tsunami struck but without an 'in situ' warning system and/or a method designed to propagate that warning, it would have been meaningless, anyway, which it was.
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