Instead of many days or even weeks, crucial data on a deadly landslide that tore through Atami, Shizuoka Prefecture, in July was released in a span of only a day.

That’s thanks to the collective work of a group of volunteer experts who located a collapsed embankment near the point of origin of the mudflow drawing on 3-D survey data that prefectural authorities had made available to everyone.

A mound of earth built in the uppermost reaches of a valley as part of land development work is believed to be responsible for the July 3 landslide, which left 26 people dead and one person still unaccounted for.

Naoya Sugimoto, 49, who works at the construction policy division of the Shizuoka prefectural government, saw a news flash about the landslide at around 10:50 a.m. that morning.

Media reports had said from the previous day that landslides caused by heavy rains were disrupting road traffic in the Izu Peninsula.

Sugimoto, a civil engineering expert who had dealt with mudflows, thought that the latest landslide could entail far-reaching damage.

Sugimoto lost no time in contacting experts in landslides, geology and data analysis, with whom he had had interactions.

He assembled a group of volunteers from the academic, industrial and government sectors on Facebook at around 3:30 p.m., about five hours after the mudflow occurred.

Sugimoto’s direct canvassing and recruitment by other members increased the Shizuoka point cloud support team to 16 members at the final count.

The first thing the team needed to do was get an overall picture of the disaster damage.

Sugimoto and his colleagues utilized “point cloud” data, which refers to a set of 3-D data points to be obtained by taking laser scanner measurements of roads, surface topography and buildings, among other objects.

The data allows a 3-D model of those physical objects to be constructed with the help of a computer, with fine details reproducible down to single power lines and tree branches, for example.

Shizuoka Prefecture is expected to suffer damage from a powerful earthquake anticipated along the Nankai Trough seabed depression south of Japan. Officials have been taking point cloud measurements throughout the prefecture from about five years ago.

In the event of a disaster, the availability of such data is expected to help calculate how much earth had collapsed through comparison with pre-disaster topography and produce maps of a disaster site.

In 2017, Shizuoka Prefecture became the first local government in the nation to release point cloud data, which is available on a website for the public to use freely. Officials expected that it would facilitate early damage analysis and restoration work.

The members of the Shizuoka point cloud support team used an online conference system and online chat to keep in touch. They first pinpointed the extent of the disaster area by using drone footage and images posted on social media.

Yusuke Suzuki, 44, who is well-versed in the topography and geology of the Atami site, analyzed the differences between measurement data from 2009 and 2019 and determined late on July 3 that the landfill lay more than 10 meters thick near the point of origin of the mudflow.

By the morning of July 4, Suzuki, who formerly worked for a land surveying company, concluded that the landfill measured about 54,000 cubic meters in volume.

Even before he joined the team, Suzuki started analysis on his own after he saw footage of areas near the origin point and noticed a multi-tiered landform, which was absent in the 2009 topographical data. He thought the feature likely represented a new mound of earth.

The team’s analysis results, including interim ones, were reported to Takashi Nanba, a vice governor of Shizuoka Prefecture, who was working at the disaster site.

The prefectural government announced on July 4 that it believed nearly all the massive landfill had apparently collapsed, expanding the scope of the damage.

“It has been customary for local governments to study and analyze disaster damage on their own or commission the work to a construction consulting company,” said Yoshiro Tanaka, 50, an employee of construction consultant Nippon Koei Co. and a member of the team.

“What we did is groundbreaking in that volunteers from different fields of expertise worked on the task together.”

The Shizuoka point cloud support team’s 3-D model was built by Shogo Numakura, 47, CEO of Symmetry Dimensions Inc., an information technology company.

“We were likely the first ones to have successfully grasped the situation in the early stages of disaster response by making extensive use of a local government’s open data as well as data from the business sector and information available on social media,” said Numakura.

Nanba, the vice governor, is a civil engineering expert who served as a technical official in the land ministry.

“I have realized the times have changed,” he told a news conference on July 15. “We used to do analysis on our own or outsource the task to a contractor. Today, people from all corners of Japan and the world will do analysis for us if we make data available to everyone.”

Nanba added, “Analysis was completed quickly. If we had chosen to set up a committee in a conventional approach, we would not have even finished selecting members. I never expected that use of open data would turn out this effective.”

Other local governments are gradually following suit. Hokkaido and Hyogo Prefecture, for example, have released point cloud data of their own in the form of open data.

“Team members were proficient in data analysis,” said Kazuhide Sawada, 53, a professor of geotechnical engineering with Gifu University, who was on the team. “In addition, they included prefectural government officials and that allowed information to be shared quickly.”

However, Sawada pointed out that the scope of responsibility often remains unclear when findings and achievements are released by a group of volunteers.

“There should be a mechanism for clearly defining roles and responsibilities, such as by assigning in advance the experts who would be working with the local government in the event of a disaster,” he said.