November 27, 850 Tsunami: NW. Honshu Island, Japan

Name: November 27, 850 Tsunami: NW. Honshu Island, Japan
Start: 0850-11-27
Location: NW. Honshu Island, Japan

November 27, 850 · Deaths: many · Definite tsunami

A tsunami caused by a magnitude 7 earthquake and a landslide began at NW. Honshu Island, Japan on November 27, 850. 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

Tsunami warnings in force

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 27, 850
Source: NW. Honshu Island, Japan
Cause: Earthquake and landslide
Earthquake: Magnitude 7
Runups recorded: 1
Tsunami intensity (Soloviev-Imamura): 1
Tsunami magnitude (Iida): 2
Waters: Ocean
How certain: Definite tsunami
Source location: 39.000° N, 139.900° E

The toll

Deaths: Many (about 101 to 1,000) with the earthquake or eruption that caused it
Damage: Moderate (about $1 to $5 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.

Reference #150:

Nov 27, 850. 39 N. 139.9 E, magnitude 7. Landslide, ground cracked. Many deaths. Mogami river sides destroyed and inundated 4 km inland from Kofufu. Tsunami damage at Kisagata.

Reference #414:

Nov 27, 850, 39.1 N, 140 E, magnitude 7.9, event validity possible. There was a strong earthquake in the Shonai locality (Yamagata Prefecture). A tsunami was observed on the coast of the Sea of Japan. Its source was presumably located to the northwest of Sakata near the coast and south of the source of the earthquake of 1804.

Probability 2, M 7.9.

Reference #1897:

Nov 27, 850. Sea waves on Japan Sea coast of northern Japan.

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
Kisagata	Japan	24		4,000	Eyewitness observation of water height

Every tsunami in 850 The 800s Tsunamis of Japan The earthquake This day in weather history Alerts 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 2026-10-01. NCEI tsunami event 69.