November 30, 1983 Tsunami: Chagos Archipelago Region, UK Territories
A tsunami caused by a magnitude 7.7 earthquake began at Chagos Archipelago Region, UK Territories on November 30, 1983 at 17:46:00 UTC. The water rose as high as 1.5 meters. Its effects were recorded at 3 places in at least 2 countries.
Where the waves reached
The source (white) and every runup with a place, colored by the water height recorded there. A ring is a runup NCEI marks doubtful.
- 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
- November 30, 1983, 17:46:00 UTC
- Source
- Chagos Archipelago Region, UK Territories
- Cause
- Earthquake
- Earthquake
- Magnitude 7.7, 10 km deep
- Maximum water height
- 1.5 m (4.9 ft)
- Runups recorded
- 3
- Tsunami magnitude (Iida)
- -1.3
- Waters
- Ocean
- How certain
- Definite tsunami
- Source location
- 6.852° S, 72.110° E
The toll
- Damage
- Limited (under about $1 million)
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.
Some damage to buildings and piers on Diego Garcia. Five foot rise in wave height in the lagoon and significant wave damage near the southeastern tip of the island. 40 cm tsunami at Victoria, Seychelles. Large zone of discolored sea water observed 35 to 40 nautical miles north-northwest of Diego Garcia. (reference #1053)
Every runup
Nearest the source first. Heights are above sea level at the time; a tide gauge reads half the wave’s full height.
| Where | Country | Km from source | Water height, m | Inland, m | Measured by | First wave, UTC | Deaths |
|---|---|---|---|---|---|---|---|
| Diego Garcia, Chagos Islands | UK Territories | 57 | 1.5 | Eyewitness observation of water height | |||
| Victoria, Mahe Island | Seychelles | 1,862 | 0.04 | Tide gauge (half the maximum wave height) | |||
| Seychelles | Seychelles | 0.4 | Eyewitness observation of water height |
More
Every tsunami in 1983The 1900sTsunamis of UK TerritoriesThe 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 2150.