The eruption of Oshima–Ōshima and the Kampo tsunami: At least 2,000 people along the Japanese coast drown in a tsunami caused by the eruption of Oshima.

The devastating eruption of Oshima–Ōshima began on 18 August 1741 and ended on 1 May the next year. Eleven days into the eruption, the Kampo tsunami with estimated maximum heights of over 90 m (300 ft) swept across neighboring islands in Japan and the Korean Peninsula. The eruption and its resulting tsunami killed at least 1,400 people. Damage was extreme along the coast of Japan, while in Korea, the tsunami damaged fishing boats.

A tsunami is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions above or below water all have the potential to generate a tsunami. Unlike normal ocean waves, which are generated by wind, or tides, which are in turn generated by the gravitational pull of the Moon and the Sun, a tsunami is generated by the displacement of water from a large event.

Ōshima is an uninhabited island in the Sea of Japan, 50 kilometers (31 mi) west of Matsumae town and therefore the westernmost point of Hokkaido. It is part of the town of Matsumae in Oshima Subprefecture in Hokkaido, Japan. To distinguish Ōshima from other islands with the same name, it is sometimes known as Oshima Ōshima (渡島大島) or Matsumae Ōshima (松前大島).

August 29 is the 241st day of the year in the Gregorian calendar; 124 days remain until the end of the year.