Officials say at least 54,000 cubic meters had been used to fill a valley in roughly the area where the mudslide began. That accounts for about half the amount of mud that flowed down, racing over a concrete barricade that had been built upstream and smashing into the community below.
Kamata, Tomoko. 2021. "Atami mudslides: landfill soil may have triggered the disaster" NHK World Japan. July 8, 2021.