HIROSHIMA, Japan - Many residents recalled unusual phenomena-smells, sounds, tremors-around the time a sediment disaster devastated an area of northern Hiroshima last week, as the investigation into what caused the disaster was in full swing on Friday.
"The area where the collapse started isn't hollowed out much. It was probably a 'surface failure,' in which there was a flow of earth and rocks near the surface," said Takashi Tsuchida, 60, a professor of geotechnics at Hiroshima University and a member of an emergency survey team examining the disaster area.
The team from the Chugoku branch of the Japan Society of Civil Engineers began their work in Hiroshima's Asa-Minami Ward on Friday morning.
Rain continued to fall on the day, increasing the amount of water flowing out of the mountains.
In the area, homes and cars crushed unmercifully by earth, rocks and sand were still visible, with huge boulders and fragments of concrete scattered around.
Rescuers continued their efforts to find people who were still missing.
The ongoing rescue effort restricted the investigation, but researchers were at least in agreement that a debris flow had occurred at the scene.
This view is backed up by testimony from local residents and others.
Many residents reported experiencing signs that are considered precursors to debris flows.
In particular, many remembered a foul smell.
"There was a smell like earth mixed with sulfur," recalled a 68-year-old woman, who said rocks and earth flowed into the ground floor of her prefectural housing unit in the Yagi district of Asa-Minami Ward.
A 70-year-old man who had muddy water flow under the floor of his house in the Yagi district said: "There were strong smells of earth, green wood and grass. This is not normal, I thought. Then I heard-boom, boom-the sound of rocks rolling."
A 67-year-old carpenter who lives in the district, also remembered the smell, as well as small tremors that lasted several minutes. This was followed by a roar, then an enormous amount of earth, and huge boulders began to flow by.
Luckily his house was not damaged, but he said, "I've never experienced such a musty smell or those tremors."
There are three types of "sediment disasters"-landslides, cliff collapses and debris flows-each with their own precursors. The testimony of these three residents is consistent with the signs that occur before a debris flow.