String of disasters kills up to one million Japanese

Eruptions started in April 1783 and became increasingly severe during June and July. Mt. Asama's major eruption on 6-7 August and maximum eruption on 8 August killed between 20,000 and 30,000 people. Pyroclastic flows obliterated Kamaharamura 12 km to the north. Volcanic ash, 400 million cubic meters, blanketed northern Kanto, 90 centimeters in Matsuido, 30 in Fujioka and Takasaki, even 10 centimeters in Sakura near today's Narita Airport.

Bodies carried downstream washed ashore at Shibamata on the Edo River; their graves are at Shibamata Taishakuten Temple in Tokyo's Katsushika Ward. Other graves are at Zenyoji in Edogawa Ward, and Ekoin in Sumida Ward.

Memorial to Mt. Asama
Victims at Ekoin

In 1783, the Tone River and its tributaries were the main transportation arteries for North Kanto into Edo. Volcanic mud flows raised river beds and changed the course of the Tone River in several places.

Before the eruption, the Tone River had major floods about once a decade; after the eruptions, major floods occurred every 3 to 5 years. A catastrophic flood in 1786 exacerbated the ongoing Tenmei famine with 1787 being unfathomably severe; one theory estimates that 1 million people died.

This flood and famine shook the Tokugawa government for the remainder of its rule. Major efforts to restore and boost the prosperity of North Kanto and the Tone River waterways all failed to deliver expected results.


Source:

1) 利根川研究会、「利根川の洪水：語り継ぐ流域の歴史」、山海堂、東京、1995. (Tone River Study Association, Floods of the Tone River: History of a Watershed that Continues to Tell Tales, Sankaido, Tokyo, 1995