Abstract
In Ajiro, Atami City, in Shizuoka Prefecture, Japan, Baiu-front stagnated from July 1 through
July 3, 2021, and 48 hours precipitation resulted in 321.0 mm (return period : 23 years) of
precipitation. On July 3rd at 10:55 a.m., a large-scale debris flow caused the collapse of the embanked
ground on the Aizome River in the Izusan District, resulting in at least 27 deaths and/or missing
persons (As of October 28). The writer surveyed 141 heavily damaged buildings. This district is
designated as collapse special caution area of steep slopes (Red zone), collapse caution area of
steep slopes (Yellow zone), and debris flow caution area (Yellow zone), and a land condition figure
presents this district’s topography as “debris flow deposits.” The precursory phenomenon was
confirmed in this debris flow disaster, but since only elderly people had been advised to evacuate
from Atami City, there were no inhabitants who relocated to the evacuation site beforehand.
