Following Monday’s deadly avalanche that killed eight people, including seven students, in Tochigi Prefecture, the authorities and experts are now assessing the decision making that led up to the incident even though an avalanche advisory had been issued for the area.
Ensuring safety on mountains is particularly difficult when groups of people are involved, according to experts — a point underscored by the deadly avalanche.
The climbing excursion, a three-day trip that began Saturday, has been held every year local high schools since 1963. This year, the group had originally planned to climb Mount Chausu on the final day, but due to heavy snow, the plan was revised to practice traversing deep snow near the ski area where the event is held.
As mountain climbing during the winter season poses many risks, the Japan Sports Agency basically bans the practice by high school students.
An official from Tochigi Prefecture said the winter season on the mountains ends in February from an operational perspective, though the central government warns visitors and residents to remain cautious through the end of May.
But the weather in the weeks leading up to the time of the accident had been unseasonal snowy and differed substantially from the usual “spring-mountain” conditions experienced in previous years.
The town of Nasu recorded 33 cm of snowfall from early Monday through 9 a.m. Beginning Saturday evening, the Utsunomiya Local Meteorological Office repeatedly warned of heavy snow conditions and issued avalanche advisories on Sunday.
It is not uncommon for groups to get caught up in avalanches during mountain-climbing training, and subsequent lawsuits often focus on the culpability of guides.
Koji Motomura, the head of a nonprofit organization ACT which engages in avalanche rescue operations, said, people have to be careful because simply walking on snow can trigger a snowslide.
“They should not have held such training if there was a risk of an avalanche in the first place,” Motomura said, emphasizing the importance for the need for informed leaders who are capable of judging snow conditions and making appropriate decisions.
Some experts suggest that the teachers may have been reluctant to call off the training, because it was effectively a compulsory event for students belonging to the alpine club. The student climbers were planning to compete in a event in May.
Mountaineering lessons are required before students can participate in climbs in April and May, according to the prefecture’s education board, a prerequisite high school principals are well aware of.
“As groups face difficulties in changing scheduled activities, they tend to force through the planned events even under bad conditions,” said Ryo Uchida, an associate professor at Nagoya University.
The risks are significant even on gentle slopes, as layers of snow are more likely to collapse if the texture is powdery, experts said. The avalanche that killed the eight people was probably a “surface avalanche,” according to the experts.
There are two common types of avalanches. A surface avalanche occurs when a layer of heavy snowfall collapses after it accumulates on top of earlier deposits of packed snow.
Another type, the full-depth avalanche, describes an event where the full snow cover slides as rising temperatures melt the snow from the ground level.
According to the local meteorological office, the amount of snow recorded on Monday was a record for late March since the office began its observations in 1990.
Weather this March has alternated between cold and unseasonal warm temperatures, increasing the risk that fresh snow piled upon solidified deposits may become unstable.
While a full-depth avalanche may show some telltale signs such as cracks or wrinkles on the slope, surface avalanches can occur abruptly without warning.
Isao Kamiishi, director of Snow and Ice Research Center of the National Research Institute for Earth Science and Disaster Resilience, said the low-pressure system that passes through the islands in the Japan’s southern shore produces snow with a simple crystal structure that tends to be more susceptible to collapse.
The tendency for new snow to break apart is magnified if the texture is powdery, even on moderate slopes, Kamiishi said.