2024/12/09 13:26
Written by Yuya Yokoyama
Temperatures this winter have been like a roller coaster ride.
Sudden wild swings in temperatures that are supposed to be warm are becoming the norm. In some areas, temperature changes of as much as six months are said to occur in a matter of days. Even though the average winter temperature is rising year after year due to global warming, I am not the only one who gets sick due to temperature differences. These temperature differences have led to avalanches as well as the human body.
You can get a sense of the fear of “avalanches” in the film “Snow Mountain Ties,” directed by J. A. Bayona and based on the true story of a Uruguayan Air Force plane that crashed in a remote mountainous area in the Andes Mountains in 1972. It is said that people can live for two to three weeks as long as they have water and sleep, but the survivors survived for 72 days from the day of the crash. In this desperate situation without water or food, they were able to survive by eating the bodies of those who died in the crash or from starvation. Although there was some resistance to “cannibalism” among them, they could not escape it as a means of survival. In this shocking film, survivor Roberto Canessa says, “The fear of hearing the sound of the mountain moving under the snow after an avalanche was worse than the pain of eating human flesh.
““I believed only that I would be saved anyway, because my heart rate would increase as my fear came up.””
Also, the “Hakuba Norikuradake Avalanche Accident” in Nagano Prefecture in 2020 has been covered by various media outlets; on February 28, 2020, professional snowboarder Nishiyama was buried by an avalanche. The probability of survival is high up to 18 minutes after burial, but after one hour the survival rate drops to 20%. Mr. Nishiyama was buried for 3 hours and 1 minute, but miraculously survived. He said that when he was caught in the avalanche, he felt as if he was “caught in a muddy stream,” and that while buried, “the weight of the snow prevented my lungs from expanding and I could not breathe,” “my heart rate would rapidly increase if I tried to move even slightly, and I had a feeling I would suffocate to death,” and “my heart rate would increase when I felt fear. I was afraid that if I tried to move even a little, my heart rate would suddenly increase and I would suffocate to death,” he said, describing the tense situation he was in at the time. Mr. Nishiyama miraculously survived, but the avalanche accidents on Mount Norikura in Hakuba were not limited to this one in 2020.
What causes avalanches and how often do they occur? I was also curious to find out what countermeasures should be taken in the event of an avalanche, so I decided to write down my findings.
Number of Fatal Avalanche Accidents in Japan
The following is the number of fatal accidents in Japan from 1991 to 2020, as announced by the Japan Avalanche Search and Rescue Council, of which Mr. Mukawa of the Japan Mountain Guides Association is the representative director. They say that the average number of fatal accidents per year is 6. The graph also shows that “recreation” related fatal accidents dominate as a percentage. Recreation is a category of leisure time activities in the snowy mountains, such as mountain climbing, mountain running, skiing, snowshoeing, snowmobiling, and mountain stream fishing. It is probably safe to say that the majority of fatal accidents (around 75%) involve avalanche accidents involving people who enjoy snowmobiling as a hobby.
(Excerpt from “Trends in Avalanche-related Fatalities (1991-2020)” by the Japan Avalanche Search and Rescue Council)
Avalanche-prone season
The highest number of avalanches occur in February, followed by January and March, he said. Also, in April and May, more damage is reported from people who went mountain climbing or mountain vegetable gathering.
(Excerpted from Weather News, “What are the conditions under which avalanches are likely to occur? Measures to Protect Lives When Encountered")
Cracks (snow cracks) ：Cracks in the snow that look like scratches on the slope.
Snow wrinkles：A fingertip-like pattern of blistered snow.
Snow cliffs：Snow overhanging the ridge of a mountain and forming a kind of eave.
Snowball：A ball-like mass of snow that rolls down a slope.
Curl：Snow is overhanging from a fence to prevent avalanche.
Snowdrift：Snow is accumulating in one place due to the wind.
Causes of avalanches
The snow on the slope is held together by three things
（寒地土木研究所 「雪崩はなぜ起きるのか」より参照）
(1) Frictional force with the ground
(2) Cohesive force between snow grains
(3) Force of falling due to gravity
An avalanche occurs when these three forces are out of balance.
(1) Factors that affect the frictional force with the ground
Snow melting due to solar radiation, temperature rise, and rainfall
(2) Factors affecting the “binding force between snow grains”
Load on the snow surface (e.g., humans, animals crossing the snow surface)
(3 ) Factors that affect the “force of falling due to gravity
Factors that affect the “force of falling snow due to gravity”
Avalanche Types
Based on the position of the sliding surface where the snow slides down, avalanches can be roughly classified into two types: “surface avalanches” and “full-layer avalanches.
An avalanche in which snow piled up on top of old snow slides down is called a “surface avalanche,” while an avalanche in which the entire layer of snow slides down from the ground is called a “full-layer avalanche.
(Excerpt from BIGLOBE News, “Types of Avalanches: ‘Surface Avalanche’ and ‘Full-Level Avalanche’”)
Surface avalanche.
It is said that the sliding surface becomes the interior of the snow cover and occurs mostly during the severe cold season when temperatures are low and snowfall is continuous (around January and February).
・When temperatures are low and snowfall is heavy
・When temperatures remain below 0°C and there are blizzards or strong winds
・When snow cover or snowdrifts form on slopes
・On 35-45 degree slopes where there are few trees showing their faces
The speed of the surface avalanche is about 100 to 200 km/h, which is about the speed of a bullet train.
Full-layer avalanche
The surface of the slope becomes the ground surface, and it is said to occur most frequently during warm periods such as the snowmelt season in early spring.
・In early spring, when temperatures rise, such as after rainfall.
・On 35-45 degree slopes, where there are no trees and the ground surface is exposed
・When snow wrinkles and cracks form and become larger
・The speed of a full-layer avalanche is about 40 to 80 km/h, about the speed of a car.
Vegetation conditions
It seems that avalanche hazard can sometimes be analyzed by studying changes in vegetation distribution.
Survey Contents
(1) Vegetation density
(2) Height of standing trees
(3) Avalanche prevention effect
(4) Height of trees above snow cover in relation to snow depth
(5) Vegetation breakage, deflection, and change in position
(6) Others (e.g., snow cover on trees, branching, etc.)
Basically, avalanches are more likely to occur on slopes with dense long grasses, even if the slope gradient is the same and the snow cover is the same. They are also less likely to occur on slopes where the tips of trees are protruding from the snow surface. Even on slopes without trees along stream banks, avalanches often strike regularly, so caution should be exercised.
Avalanche Hazard Areas in Japan
More than half of Japan's land area is designated as a “heavy snowfall area,” and the total number of avalanche hazard areas nationwide in 2004 was estimated at 20,501. The following are the top 5 avalanche hazard areas.
Hokkaido: 2,536
Akita: 1,630
Gifu: 1,630
Niigata: 1,484
Fukui ： 1,318
What to do if you are caught in an avalanche
Anyone caught in an avalanche would be prepared to die. In such a desperate situation, it is necessary to remain calm and unyielding so that one's fear does not get the better of one's mind, as it did for Mr. Nishiyama when he was involved in the avalanche accident on Mount Norikura in Hakuba, Japan.
(Excerpt from “Preparing for Heavy Snowfall - What kind of disasters can occur from snow damage” on the Cabinet Office's Disaster Prevention Information page)
“There is no doubt that the effects of human activity have warmed the atmosphere, oceans and land.”
As noted at the outset, the recent weather is unusual. The Intergovernmental Panel on Climate Change (IPCC) asserts that “there is no doubt that the effects of human activity have been warming the atmosphere, oceans, and land,” and that human activity has undoubtedly contributed to the warming. If no further measures are taken to reduce greenhouse gas emissions, it is likely that greenhouse gas emissions will rise by about 4 degrees Celsius by the year 2100. If the temperature can be kept below 2 degrees Celsius, there will be benefits such as “contribution to health,” “reduced impact on ecosystems,” “sufficiency of resources,” and “contribution to the robustness of energy systems,” among others. The longer countries around the world delay taking action, the closer to impossible it will be to keep the temperature below 2 degrees Celsius, and knowledgeable scientists have pointed this out. I am not alone in feeling that we all need to join hands for the sake of Mother Earth.
