The eruption of Mount Ontake on Saturday was the worst in postwar history, with nearly 50 people confirmed dead. And it could be some time before the full toll is known.
Dozens are reported missing, but figures vary widely and no official entity — police, fire or government — can say for sure how many bodies may lie buried amid the rocks and ash.
One reason for the lack of clarity is that only a fraction of hikers bother to notify rangers they are embarking on a trek. Although recommended, it is not mandatory to do so.
As local authorities reveal the limits of their data, relatives and friends of the missing are frustrated with the lack of information.
On Tuesday afternoon, the fire department at nearby Kiso, Nagano Prefecture, said 79 people were unaccounted for, later trimming the figure by eight after the whereabouts of some were confirmed.
The prefectural government then dismissed the list, saying it was inaccurate and that officials were rechecking the data.
Many people awaited news at a conference room with a TV at the municipal offices in the town of Kiso. On Tuesday one person there expressed exasperation, saying they were learning more from TV than the local officials and that they might as well have stayed home.
Yohei Matsumoto, a parliamentary vice minister at the Cabinet Office, visited the town and met relatives, but it seemed that neither the minister nor town officials had much to give them.
“Information isn’t coming freely, even at the disaster measures headquarters,” a town official said.
The problem stems in part from the difficulty of knowing how many people set off that day for the 3,067-meter volcano, which straddles Nagano and Gifu prefectures.
Police data showed 303 people registered that day in Nagano and 30 in Gifu.
But there were probably far more than 333 people on the mountain when it unleashed havoc on Saturday.
An association that represents Kiso and five other nearby towns and villages says climbers in the autumn foliage-viewing season typically number in the several thousands per day.
The association estimates only 10 to 20 percent of walkers register as they set off.
The inability to determine the actual number of climbers can lead to delays in response when disaster strikes, an issue that troubles officials elsewhere in Japan wherever there are busy mountain trails.
In central Hokkaido, an attempt has been made to address the problem.
The Daisetsuzan National Park, which covers peaks such as Mount Tomuraushi and Mount Tokachi, has installed infrared sensors at more than 10 trail entry points to count those who pass.
Data is also used to assess the environmental impact and where trail repairs may be needed.
The Environment Ministry, which manages the park, says nearly 90 percent of climbers would register if there was a manned office at the trail opening.
Park ranger Hiroshi Nogawa, 39, said that since the registration book can be viewed by anyone, some hikers may be reluctant to register, as “people are increasingly sensitive to protection of private information.”
But a 56-year-old official of the Kiso municipal association said, “All we can do is to urge people to submit climbing registrations so that we can promptly grasp potential damage and provide necessary information.”