Poorly stacked soil seen behind a deadly mudslide in central Japan

This photo, taken from a Kyodo News helicopter on July 6, 2021, shows the site of a massive mudslide triggered by torrential rains in the spa town of Atami, in central Japan’s Shizuoka Prefecture, with the arrow pointing to the approximate starting point. (Kyodo)

SHIZUOKA, Japan (Kyodo) – As search efforts continue for 21 people missing from a massive mudslide that hit a spa town in central Japan last weekend, experts and the local authorities suspect an inappropriate accumulation of soil at the origin of the disaster.

Local authorities say about 54,000 cubic meters of soil that had been brought to the mountainside by a property management company exacerbated the massive July 3 mudslide in Atami, Shizuoka Prefecture, resulting in the death of nine people.

Some 56,000 cubic meters of soil in total, mostly land left by the company, collapsed into a nearby river, traveling a distance of about 2 kilometers. About 130 houses and buildings were destroyed or damaged.

The property management company based near Odawara in Kanagawa Prefecture, which acquired the mountainside land in 2006, brought soil in excess of the amount declared to the local authority and also mixed waste with it. industrialists, according to the government of Shizuoka prefecture.

The now liquidated company is also suspected of failing to install drainage facilities at the site as required by an order from Shizuoka Prefecture, the prefectural government said.

The real estate company said in a 2009 report to the prefectural government that it planned to install an underground pipe as drainage, but such a device was not confirmed in photos or other material taken after the mudslide. , according to Shizuoka vice-governor Takashi Namba.

The company has been the subject of several administrative instructions from the prefectural and municipal governments of Atami due to repeated inappropriate actions, the Shizuoka government said.

For example, the company announced in 2009 that it intended to pile soil on the ground to a height of 15 meters, but the actual height from the ground reached around 50 meters shortly before the mudslide, according to the prefectural government. .

The company also underreported the area of ​​forests it felled nearby and the prefectural government asked it to restore it in 2007.

The Geospatial Information Authority of Japan said the soil at the site would have increased by about 56,000 cubic meters between 2009 and 2019 and that 85%, or about 48,000 cubic meters of the soil, could have drained during of the last mudslide.

The authority, which made the prediction using data from airborne laser surveys, said a site that was a valley in 2009 had been raised to a height of up to 13 meters in 2019 due to of soil build-up.

In the aftermath of the mudslide, the central government took steps to ensure the safety of accumulated soils located across the country, including discussing the creation of universal regulations.

At present, Japan does not have comprehensive legal regulations covering soil accumulated for purposes such as residential land development or disposal of excess soil.

The local governments that treated the piled up soil by ordinances asked the central government to establish uniform rules.

“We need to establish firm rules and make sure they are followed by operators,” Land Minister Kazuyoshi Akaba said, noting that accumulated soils not regulated by law present a “high risk”.

Akaba said his ministry would discuss the matter with relevant government agencies, including ministries of forests and the environment. The entities will also explore ways to inspect and reinforce land with accumulated soil in danger of collapsing across the country.

Masato Koyama, professor at the Shizuoka University Center for Integrated Research and Education on Natural Hazards, warned of a recurrence of mudslides, as there are still around 20,000 cubic meters of fragile soil accumulated. on the site.

Koyama, who conducted an on-site investigation on Monday, said in his report that the soil that triggered the mudslide did not include volcanic rocks naturally seen in the area but consisted mostly of small stones mixed with sand, indicating that it had been brought in from outside.

He also concluded that since there were no large volcanic rocks found in the areas affected by the disaster, the mudslide came only from the accumulated soil.

Koyama estimated that about 55,000 cubic meters of accumulated soil collapsed and caused the mudslide.

“I suspect that the accumulated soil collapsed due to an increase in groundwater caused by heavy rains,” said the professor.

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