Most avalanches occur in winter or in spring when the snow is very heavy, especially before or after the blizzard. At the time, the snow is very soft, and the adhesion force is small. Once a small piece is destroyed, the rest will be like a chain of sand or dominoes, causing chain reaction so that it decline rapidly. In the Spring, due to the thawing period is long, as the temperature rises, the snow on the surface will melt and the snow water will trickle to infiltrate into the depths of the snow layer and lets originally strong snow become loose, greatly reducing the cohesion and anti-breaking strength between the snow and making the snow slide more easily between layers.
The severity of an avalanche depends on the volume, temperature, and slope of the snow, especially the slope. The most terrible avalanche slope often occurs in 25 ~ 50 ° slope. If the mountain is too steep, there will not be enough snow and if the slope is too small, it is not very likely to form an avalanche. Like floods, avalanches are repeatable phenomenon, too. That is to say, if an avalanche occurs somewhere, it is likely to return soon. It is possible that an avalanche occurs every year or every century in the same place after every snow. These all depend on the characteristics of terrain and certain climatic factors.
The number of avalanches is also related to climate and terrain. Winter snow and avalanches in central Tianshan often block mountain roads. However, the frequent occurrence of avalanches in Nianqing Tanggula and Hengduan mountains is one of the important sources of modern glacier development.
Choosing the right time to climb the mountain in this area is harsh. At the same time, the Kunlun Mountains near the inland in the west of our country, Tanggula Mountains, Qilian Mountains, there are less rainfall, without clear dry and rainy season so avalanche is less and choosing suitable hiking time is comfortably off.
In addition, these inland mountains are relatively low in height, generally between 1000-1500 meters, so the slope of the mountain is also moderate. However, the Himalayas and Karakoram are at a height of 3,000 ~ 4000 meters and even 5000 ~ 6000 meters. Therefore, the mountain slope is steeper, and the possibility of avalanches occurrence and the potential energy of snow slides are greater.
There is also rule of space and time for avalanches. For our country mountain, mountains on westsouth border such as the Himalayas, Nianqing Tanggula and Hengduan Mountains, due to the control system of Indian Ocean season, annual rainfall is rich except the clear cut of rainy season and dry season. The upper mountain gets more snow in winter and spring, so avalanches happens more easily.
In addition, In Tianshan Mountain, Altai Mountains, winter and spring precipitation is also more because of the Arctic Ocean polar air mass, so this season avalanche occurs more frequently.
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