December 21, 1755 Tsunami: SW Portugal
A tsunami caused by an earthquake began at SW Portugal on December 21, 1755 at 09:00 UTC. It killed 300 people, counting the earthquake or eruption that caused it.
Where the waves reached
The source of the tsunami. No runup with a place is recorded for it.
- Under 1 m
- 1 to 3 m
- 3 to 10 m
- 10 to 30 m
- 30 m and more
- Height not recorded
Travel times
How long the first wave took to reach each part of the ocean, one line for each hour up to 24, estimated from the source and the depth of the sea.
The travel times are computed in your browser, which needs JavaScript.
- 1 to 4 hours
- 5 to 6 hours
- 7 to 14 hours
- 15 hours and more
Computed in your browser the way NOAA’s own travel time maps are: the wave travels at the square root of gravity times the depth, over NOAA’s ETOPO1 depths averaged to a 10 arc-minute grid. Checked against NOAA NCEI’s maps for 21 tsunamis over the first 24 hours, these lines fall within 10 minutes of NCEI’s at half the points compared and within 52 minutes at 9 in 10. They give when the first wave could arrive, not how high it is; bays, harbors and island chains finer than the grid can see it later. Not for use in a warning: see tsunami.gov.
The tsunami
- Date
- December 21, 1755, 09:00 UTC
- Source
- SW Portugal
- Cause
- Earthquake
- Earthquake
- The earthquake
- Runups recorded
- 0
- Waters
- Ocean
- How certain
- Questionable tsunami
- Source location
- 37.000° N, 10.000° W
The toll
- Deaths
- 300 with the earthquake or eruption that caused it
- Damage
- Moderate (about $1 to $5 million) with the earthquake or eruption that caused it
- Houses destroyed
- Some (about 51 to 100) with the earthquake or eruption that caused it
Where the literature gives no number, NCEI records a description on a scale of 1 to 4, printed here in its words. Damage is in millions of US dollars of the year of the event, not adjusted for inflation.
What the record says
NCEI’s account, from the sources it cites.
Victims due to Tagus flood. Questionable tsunami. (reference #4139)
A description of a tsunami the 21 December 1755 is included in Rodriguez (1932): “[. . . ] At about 9 an earthquake occurred in Lisbon, with two shakings of short duration but so violent that caused damage and ruin in the city. The Tagus overflowed. 300 people died in the rubbles and drowned in the waters of this river [. . . ] the realm of Algarve suffered a lot. At the coast the sea advanced one league. People at Spanish frontier suffered less [. . . ]”. Rodriguez (1932) quotes no original source for the information. This event is not mentioned in any coeval sources of the Portuguese archives. Mendonca (1758) devotes the final part of his catalog to the aftershocks sequence of the 1755 earthquake and there is only one event with associated tsunami (the Coruna 16 November 1755 event): “[. . . ] on the 21, by 9 o’clock (in the day) there was one that caused so violent concussions, that caused in Lisbon and surroundings some ruins. If it lasted more, there would certainly be more damage”. (Mendonca, 1758, p. 62) (reference #4649)
More
Every tsunami in 1755The 1700sTsunamis of PortugalThe earthquakeThis day in weather historyAlerts in force
Sources
Tsunami events and runups from NOAA’s National Centers for Environmental Information, Global Historical Hazard Database, cited as NCEI/WDS, doi:10.7289/V5PN93H7. Public domain. Read 2026-09-24. NCEI tsunami event 4266.