Massive soil mound on slope seen as worsening Japan mudslide

TOKYO (AP) — A powerful mudslide that killed at least seven people and destroyed dozens of homes in a Japanese seaside resort started in an area with a history of land alterations, and a massive mound of soil piled there broke off and worsened the devastation, officials said Wednesday.

They said more investigation is needed to determine if the mound was the primary cause of the disaster in Atami, where hundreds of rescue workers and dogs searched Wednesday for missing people inside homes destroyed and filled with mud.

Twenty-five people were still unaccounted for since the mudslide hit Saturday, according to Shizuoka prefecture and Atami city officials. Determining an accurate number of missing is difficult because many Atami residences are second homes or vacation rentals.

The mud exposed after the slide ripped through streets and homes was distinctively black, showing it contained large amounts of abandoned soil from the area where the land alterations had been made.

The mound of soil was improperly built, Shizuoka prefecture Vice Gov. Takashi Namba said after an initial assessment.

“We can at least say that the severity of the disaster was amplified by the more than 50,000 cubic meters (1.8 million cubic feet) of soil in the mound that had been sitting there,” said Namba, a former land ministry official and civil engineer.

He noted the area also had other land development, including a solar power generation complex, deforestation, a housing complex and an apparently illegal industrial waste dump. He said geological details suggest the solar complex and housing development were not the cause of the mudslide, though a further examination is needed.

Construction of the mound began in 2009 under a plan to bring in 36,600 cubic meters (1.3 million cubic feet) of soil for a height of 15 meters (50 feet) and was completed in 2010. In the process, contamination of the soil with plastic and wooden waste was found and the owner was ordered to remove them, suggesting it was a waste dump rather than for development, Namba said.

A survey of the area in 2020 showed that the mound was 50 meters (164 feet) high, suggesting an unauthorized addition of several layers during the past decade, the vice governor said. The land was sold to a new owner in 2011.

Officials are checking ownership changes and unauthorized land alterations related to the mound and other projects.

Namba said he believes the mound was built poorly, without reinforcement or adequate drainage in a location rich with groundwater.

Prefectural officials are discussing ways to prevent further erosion and landslides in the area.

He said decades-old ordnances related to forestry and land may need to be toughened to regulate waste dumping and land use.

An assessment is planned of other land developments around the country, land ministry officials said.

The landslide occurred after days of heavy rain in Atami, which like many seaside towns in Japan is built into a steep hillside. The town has a registered population of 36,800 and is about 100 kilometers (60 miles) southwest of Tokyo.

The disaster is an added challenge for Prime Minister Yoshihide Suga as authorities prepare for the Tokyo Olympics, starting in about two weeks. Japan is still struggling with the coronavirus pandemic.

Early July, near the end of Japan’s rainy season, is often a time of deadly floods and mudslides, and many experts say the rains are worsening due to climate change.

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