December 21, 1939 Tsunami: N. Moluccas Islands, Indonesia
A tsunami caused by a magnitude 8 earthquake began at N. Moluccas Islands, Indonesia on December 21, 1939 at 21:00:40 UTC. Its effects were recorded at 2 places.
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
- December 21, 1939, 21:00:40 UTC
- Source
- N. Moluccas Islands, Indonesia
- Cause
- Earthquake
- Earthquake
- Magnitude 8, 150 km deep
- Runups recorded
- 2
- Waters
- Ocean
- How certain
- Probable tsunami
- Source location
- 0.000° N, 123.000° E
The toll
- Damage
- Limited (under about $1 million); Moderate (about $1 to $5 million) with the earthquake or eruption that caused it
- Houses destroyed
- Many (101 to 1,000) 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.
December 22, 1939, 21:00:40 UTC, 0 N, 123 E, depth 150 km, magnitude 8 MS. There was a destructive earthquake with source In Tomini Bay. During the earthquake, oscillations in sea level apparently developed. They were especially marked on the south coast of the Minahassa Peninsula. Rice fields were flooded at Langoan. (reference #414)
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 |
|---|---|---|---|---|---|---|---|
| Langoan (Langowan) doubtful | Indonesia | 245 | Eyewitness observation of water height | ||||
| Minahassa Peninsula | Indonesia | Eyewitness observation of water height |
More
Every tsunami in 1939The 1900sTsunamis of IndonesiaThe 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 1738.