September 8, 1948 Tsunami: Tonga Trench
A tsunami caused by a magnitude 7.8 earthquake began at Tonga Trench on September 8, 1948 at 15:09:00 UTC. The water rose as high as 0.1 meters. Its effects were recorded at 7 places in at least 4 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
The tsunami
- Date
- September 8, 1948, 15:09:00 UTC
- Source
- Tonga Trench
- Cause
- Earthquake
- Earthquake
- Magnitude 7.8, 33 km deep
- Maximum water height
- 0.1 m (0.3 ft)
- Runups recorded
- 7
- Tsunami intensity (Soloviev-Imamura)
- 1.5
- Tsunami magnitude (Iida)
- 1
- Waters
- Ocean
- How certain
- Definite tsunami
- Source location
- 21.000° S, 174.000° W
The toll
The record gives no deaths, injuries or damage for this tsunami.
What the record says
NCEI’s account, from the sources it cites.
1948, September 9, (03:30). An earthquake in the area of the Tonga Islands generated a tsunami which was recorded on tidal gauges (Reference #415).
The first test of the system [Seismic Sea Wave Warning System] came in connection with the Tonga Islands earthquake of September 8, 1948. Although no warning was issued and only a 6-inch wave arrived at Honolulu (reference #13565)
Unofficial warning was issued (reference #335)
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 |
|---|---|---|---|---|---|---|---|
| Pago Pago, American Samoa, AS | US Territories | 823 | 0.1 | Tide gauge (half the maximum wave height) | |||
| Rarotonga | Cook Islands | 1,480 | Eyewitness observation of water height | ||||
| Fort Denison, Sydney Harbor | Australia | 3,698 | Tide gauge (half the maximum wave height) | ||||
| Hilo, Hawaii, HI, HI | United States | 4,956 | 0.1 | Tide gauge (half the maximum wave height) | day 8, 22:15 | ||
| Honolulu, Oahu, HI, HI | United States | 4,998 | 0.1 | Tide gauge (half the maximum wave height) | day 8, 21:45 | ||
| Port Allen, Kauai, HI, HI | United States | 4,999 | 0.1 | Tide gauge (half the maximum wave height) | |||
| Waianae, Oahu, HI, HI | United States | 5,000 | 0.1 | Tide gauge (half the maximum wave height) |
More
Every tsunami in 1948The 1900sTsunamis of TongaThe 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 1784.