Why does the snow on the mountain not melt all the year round?

Because the snow height above these mountains is above the snow line, the temperature above the snow line is low, and the annual supply of ice and snow is greater than the melting amount, forming a perennial snow area; Below the snow line, the temperature is high, and the annual supply of ice and snow is less than the melting amount, so it is impossible to accumulate ice and snow for many years, only in seasonal snow-covered areas; Near the snow line, the annual snowfall is equal to the annual melting, reaching a dynamic balance.

The position of the snow line in a place is not fixed. Seasonal changes will cause the snow line to rise and fall: in summer, the temperature is higher and the snow line rises; In winter, the temperature drops and the snow line drops. This temporary boundary is called seasonal snow line. Only in summer, the position of the snow line is relatively stable and returns to a relatively fixed height every year. Therefore, the height of the snow line is measured in the hottest month of summer.

The distribution height of the snow line is positively correlated with the temperature, and the snow line is also high when the temperature is high. With the decrease of ground temperature from low latitude to high latitude, the general trend of snow line distribution height is to decrease from low latitude to high latitude. For example, the height of the snowline in tropical Africa is 4500 ~ 5200m, while that in Alps is 2400 ~ 3200m, and it is only below 100m in the Arctic Circle.

Extended data:

The snow on the mountain below the snow line does not melt in winter in mountainous areas, but is melted by the sun in spring, forming a rare flood season in inland rivers.

The flood season when snow melts into water in warm spring is called spring flood. Because the melting of snow needs to consume a lot of heat. So in the spring flood season, the temperature on the earth can't rise yet, and there will be a period of late spring cold. Every summer, the Yangtze River, the Yellow River and other major rivers in China have to fight floods, because this is the flood season of these rivers, and the rivers have the largest amount of water.

However, some rivers in the world, such as the Irtysh River, ob river River, Yenisei River and Lena River in the Soviet Union, have their main flood season not in summer but in spring, and the spring flood season is the largest in the whole year, far exceeding the scale of summer flood season.

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