July 20, 766 Tsunami: N. Kagoshima Bay, Japan
A tsunami caused by a volcano began at N. Kagoshima Bay, Japan on July 20, 766. Its effects were recorded at 1 place.
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
- July 20, 766
- Source
- N. Kagoshima Bay, Japan
- Cause
- Volcano
- Earthquake
- Magnitude 6.5
- Volcano
- The eruption that caused it
- Runups recorded
- 1
- Tsunami intensity (Soloviev-Imamura)
- 1.5
- Tsunami magnitude (Iida)
- 1.5
- Waters
- Ocean
- How certain
- Definite tsunami
- Source location
- 31.600° N, 130.700° E
The toll
- Deaths
- Many (about 101 to 1,000)
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.
July 20, 766, 31.6 N, 130.7 E, magnitude 6.5, validity 4, tsunami intensity 1.5. Volcanic eruption at Shinzo Shinto. Many people washed away and killed at Osumi, Kagoshima Prefecture. (from reference #150)
July, 765 [probably same event as July 766], 31.6 N, 130.9 E, validity 1. There was a volcanic eruption and short-period tremors on Kyushu Island, north of Kagoshima Bay (Osumi Peninsula) at Shinzoshinto. According to some chronicles, the island subsided. People were washed away, This probably refers to a mud flow, and not to a tsunami. (reference #414)
July 765 (or July 20, 766). At Shinzo Shinto. Volcanic eruption. Rapid shaking. Island sank by some reports. A number of people swept away. Probably a mud flow, not a tsunami. Gondo (reference #4019) gives earlier year; Musya (reference #3462) and Arakawa (reference #4021) later.(reference #79)
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 |
|---|---|---|---|---|---|---|---|
| Osumi Island | Japan | 190 | Eyewitness observation of water height |
More
Every tsunami in 766The 700sTsunamis of JapanThe earthquakeThe eruptionThis 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 61.