Many peaks in the world are covered with snow all year round, like wearing a "white hat", which will not disappear even in hot summer. Even in some tropical mountainous areas, such as Kilimanjaro in Africa, Himalayas in Asia and so on. Why is this? Because the weather in mountainous areas is much colder than that in plains in the same area.
So, why is it so cold on the mountain? Because the higher the mountain, the thinner the air, and the easier it is to lose heat from the sun. The temperature will drop by about 0.6℃ per 100 meter, so at a certain height, the temperature will drop below 0℃, and the ice and snow will not melt all year round. The dividing line of this height is called the snow line. The closer you get to the poles, the lower the snow line is, because the weather there is already very cold; The closer to the equator, the higher the position of the snow line.
Also, after the top of the mountain is covered with snow and ice, 50% ~ 90% of the sunlight irradiated here is generally reflected due to the strong reflection of sunlight on the snow and ice surface, which makes the temperature here low and the snow and ice are not easy to melt.
So at the top of the mountain above the snow line, there will be snow all year round. Of course, it will snow here, and there must be a place to pile up snowflakes on the top of the mountain. Therefore, not all mountains can accumulate ice and snow. The snow and ice on those snow peaks are not absolutely constant all year round. If there is strong sunlight, some will melt. But soon after, it was supplemented by snowfall, so the snow and ice can always exist, forming a glacier to move down.
"Rome was not built in a day." Those "white hats" on the top of the mountain were not formed overnight, but gradually changed from snowflakes.
When the snow just fell to the top of the mountain, the interior was porous and loose, with about 40% ~ 50% gaps. The snow on the top of the mountain melts on the surface of the snow under the irradiation of the sun during the day, and the melted water penetrates into the lower layer of the snow to drive away the air in the snow, and the weight of the snow can also compress itself. At night, the temperature drops, melting water and snow freeze together, so there is ice in the snow, snow in the ice, melting and freezing, and snow becomes translucent granular snow.
Later, the new snow was covered with granular snow, which increased the pressure, compressed more tightly, had fewer internal gaps and lowered the melting point. After continuous melting and freezing, granular snow finally turned into light blue glacier ice. As time goes by, glacier ice is getting closer and closer, forming glaciers to move down the mountain.
The temperature on the earth is constantly changing. When the temperature decreases, the snow line will decrease, the number of mountains that can be covered by snow will increase all year round, and the scale of glaciers will expand. When the temperature rises, the area of glaciers will shrink.