The poet depicts the beauty of ice and snow, and also records the "darkness" of ice and snow.

As the New Year is coming to an end, the children in the south are preparing to go home for the New Year with their bags and bags, but when they arrive at the train station, they find that many routes are either suspended or delayed. Those who choose to drive back find that many highways are closed when they check the highways. What's going on? In fact, it's all the ice and snow behind the scenes!

When it comes to ice and snow, the first thing that comes to people's mind is the grandeur of "the scenery of the north, thousands of miles of ice and snow", followed by the agreement between Bai Juyi and Liu Shijiu that "the sky is about to snow in the evening, can you drink a cup?", the silence of Liu Zongyuan's "the birds are gone in the thousands of mountains, and the people are gone in the thousands of paths", and the agricultural proverb "this winter, the wheat is covered with three layers of quilts, and next year, you will sleep on steamed buns, and the snow is a sign of a good harvest." For humans, ice and snow always give people infinite reverie and imagination, and have become a scene that literati and ordinary people from ancient times to the present like, and they recite it constantly. But as a climate and geological phenomenon, while ice and snow bring joy and peace to people, their powerful geological destructive effect should not be underestimated. This point is not only discovered by us modern people, but also by the ancients, who felt the same and recorded it in poetry !

Freeze-thaw disaster

The sun is warm and the snow is half melted (Tang Dynasty, Du Mu) . The background of this poem is that in the early spring of 839 AD, outside Xuancheng, Anhui, the sun was warm and the snow accumulated for a year slowly melted, and the road for a long journey was covered with mud. The spring breeze was chilly, and the season of ice and snow freezing and thawing was just the time of parting. The muddy melting snow also vaguely set off and foreshadowed the poet's worries about his friends and his future. As a typical physical weathering process, freeze-thaw is accompanied by the entire process of ice and snow formation, melting and evaporation. In winter, as ice and snow form, the surface rock strata cool down rapidly, and then melt quickly when the weather warms up. After melting, some snow water invades rocks or rock cracks, and turns into ice again at night or when the temperature drops.

Figure 1: An old greenhouse building with icicles hanging from the roof during the freeze-thaw cycle in winter (copyright image of the library, reprinting and use may cause copyright disputes)

South wind melts snow, north wind condenses (Song Dynasty, Yang Wanli). There is white snow in the south, which freezes into ice in the morning and evening . The warm south wind melts the snow, while the cold north wind makes it condense again. Snow, as a form of water, switches freely between solid and liquid as the temperature changes. However, since the density of ice is less than that of water, about 0.9 g/cm3, when snow water is converted into ice, its volume expands by about 10%, which has a strong splitting effect on the surrounding rock, thereby expanding the volume of the cracks when water invades, causing more snow water to invade and produce a greater splitting effect. This cycle repeats 25 times, and in theory, the cracks at the time of invasion can be expanded to 10 times the original size. On the one hand, the increase in the volume of the cracks increases the instability of the rock mass; on the other hand, it also causes the rock mass to be immersed in 10 times the amount of water that invaded the original cracks, increasing the instability of the rock mass, and thus increasing the probability of landslides or collapses. Once the critical value is reached, sliding and collapse will form a geological disaster.

Freezing rain disaster

The Chu River is thinly frozen (Tang Dynasty, Meng Jiao) . This poem describes the southern Chu region, where the climate is warm and humid most of the time in winter, with occasional short-term cold weather, and the river water only forms a thin layer of ice. Freezing rain is a type of precipitation that appears in early winter or late winter and early spring, consisting of a mixture of ice and water and freezes immediately after landing.

The freezing rain is half snow, and the tourists' shoes are frozen and slippery (Su Shi, Song Dynasty) . This poem describes the freezing rain in the south, which is half rain and half snow. It turns into ice when it falls on the ground, making it difficult for people to walk. As a disastrous weather, when freezing rain falls on objects with a temperature below 0℃, it immediately freezes into a smooth and transparent ice layer. When the ice layer is thick enough, it will break trees, electric poles, and power transmission lines, causing communication, power supply and traffic to be suspended, and even threaten the flight safety of aircraft in the air. Cold rain falls on the river at night in Wu (Wang Changling, Tang Dynasty). As a meteorological phenomenon, freezing rain generally occurs more frequently in the south.

Figure 2: On November 8, 2021, in Pingfang District, Harbin, a traffic auxiliary police officer directed traffic in freezing rain. (Source: Xinhua News Agency)

The climate in northern Hebei has changed recently, and the winter is warm and peaceful. Last year, I remember the road to the south of the Yangtze River, with freezing rain and snow flying everywhere (Xie Duo, Ming Dynasty ). In the eyes of Xie Duo, a poet of the Ming Dynasty, the winter weather in Hebei is sunny and warm, which is completely different from the freezing rain and snow flying in the south of the Yangtze River last year. China is vast and rich in resources. The north and south span a large latitude and have a large climate difference. At that time, freezing rain will almost become a specialty of the south. Although freezing rain rarely occurs in northern China, once it occurs, its destructive power cannot be underestimated. It will cause large-scale damage to power supply, water supply, transportation, agriculture, etc.

Ice Flood

The sun rises and the snow melts on the mountain and the river rises ( Su Shi, Song Dynasty ). This poem describes the sun coming out, the warm sunlight melts the snow and gathers into water to flow into the river, and the water level of the river rises sharply with the melting snow. The poet used simple and concise language to describe a river geological process caused by the natural melting of ice and snow. This is actually a true portrayal of the process of ice flood. Ice flood, also known as "ice row", refers to the hydrological phenomenon that ice blocks the river channel in winter, causing the water level in the upper reaches to rise, resulting in embankment breach and flooding. From the cause of formation, ice flood is mainly affected by air temperature, water temperature, flow and river channel morphology. In particular, the river channel or river section where the upstream river ice melts first or the downstream river water freezes first is very prone to ice flood. In northern China, the Yellow River, Heilongjiang River and Songhua River are all rivers with high incidence of ice flood, especially in the winter river closure period and spring river opening period. Among them, the ice flood in the Yellow River during the river opening period every year is elegantly called "peach blossom flood" because it occurs when the peach blossoms along the coast are in full bloom. In addition to raising the water level and causing the river to flow back and flood, another significant destructive power of ice flood is its huge destructive power. This is because ice flood is formed by river water and ice, and its overall density is greater than that of river water. According to the kinetic energy quantification, the greater the density, the greater the potential energy, that is, the greater its destructive power.

Figure 3: On December 17, 2023, floating ice appeared for the first time this winter in the Ningxia section of the Yellow River. (Source: Xinhua News Agency)

Of course, facing the huge destructive power of ice flood, in the eyes of poets, it is indeed another spectacular and beautiful scene. For example, Liu E, a writer and poet famous for "The Travels of Lao Can" in the late Qing Dynasty, wrote about the spectacular ice flood in Qihe in 1892 at the Qihe Yellow River Control Site - "The ground cracked, the north wind howled, and the long ice covered the river. The ice behind chased the ice in front, and the ice overlapped and overlapped. The river bends were easily blocked, and the rugged silver bridges were built." In the cold winter, the north wind was howling, and the floating ice on the river surface chased and overlapped, filling the river. When passing through the meandering river, due to the difference in flow speed inside and outside, the floating ice stacked on each other, like a silver-white ice bridge under the sunlight. The poem vividly describes the spectacular scene of the Qihe ice flood under the cold north wind, the overlapping of floating ice blocking the meandering river to form an ice bridge. Also in the North China Plain, Emperor Qianlong wrote about the Yongding River and the ice flood during the Jingzhe season: "Looking down from the railing, I can see the fierce muddy current, and the layers of ice piled up in the river bank", which means the spectacular scene of the river ice pouring down the Yongding River when the ice flood passed by. The talented Li Bai used the extremely romantic and symbolic "I want to cross the Yellow River, but the ice blocks the river", using the Yellow River ice flood blocking the river to compare the poet's own difficult career and unfulfilled ambitions. It is very touching to read!

Conclusion

When the six-petaled flowers fly into the house, sit and watch the green bamboos turn into white branches ( Gao Pian , Tang Dynasty). When we sit quietly in front of the window, watching the snowflakes drift into the courtyard, the green bamboos outside the window turn into pure white branches. In fact, apart from causing occasional disasters, ice and snow are mostly a favorite for people to entertain their body and mind. In addition, in addition to decorating the white world, the "cold" ice and snow also have her warm side - promoting the global freshwater cycle. As a form of existence of water bodies, about 10% of the earth's surface is covered by ice and snow for a long time, supplying 70% of the earth's fresh water and becoming a reliable water source for human survival and development. On the other hand, ice and snow, with its rapid transformation form and huge external force, have become an important geological role in promoting the evolution and progress of the earth's surface, and play their own unique role in the evolution of the ecology and landforms of the earth's surface.

Figure 4: Water cycle process (copyright image from the library, reprinting may cause copyright disputes)

Author: Liu Hanbin, Senior Engineer, Shanxi Coal Geology Bureau

Produced by: Science Popularization China

Produced by: China Science and Technology Press Co., Ltd., China Science and Technology Publishing House (Beijing) Digital Media Co., Ltd.