Formation and characteristics of karst
"Karst" was originally the name of a limestone plateau at the junction of northern Yugoslavia's Istra Peninsula and Italy. The karst landform there is quite typical, so people use the word "karst" to represent karst landform. 1966 The word "karst" was officially changed to Chinese karst, which is the general name of karst and karst landforms. The destruction and transformation of soluble rocks such as limestone, dolomite, gypsum and rock salt by surface water and groundwater are mainly chemical processes (dissolution and precipitation), supplemented by mechanical processes (erosion and deposition by running water and gravity collapse and collapse), which is always called karstification. The underground form formed by karst is called karst landform. Because karst landform is the most widely distributed and typical one in limestone strata, it is also called limestone landform in some textbooks. The main types of karst landforms are stone buds, stone gullies, stone forests, caves, tiankeng, underground rivers, caves, caves, blind valleys and peak forests.
The first condition to form karst landforms is to have soluble rocks, such as limestone (mainly composed of CaCO3) and dolomite (MgCO3). Secondly, water flow plays a leading role in the formation and development of karst. Water flow is the driving force of karst development. In the early stage of karst process, it was divided into limestone-like bedding by vein fissure water, medium-term dendritic tube water, mature comb tube hole water and layered hole water, which made the landform of peaks and valleys appear, and then evolved into wide valley landform dominated by hills and towers, and underground karst caves developed. Furthermore, the karst landform is closely related to the overall rise and fall of the area and its speed. For example, karst development areas in South China all belong to uplift areas or strong uplift areas. According to the calculation, the step elevation in Hunan, eastern Sichuan, southwestern Hubei, Guizhou and Yunnan is about 65,438 0.200m, and the average annual relative rising speed is over 65,438 0.5mm. This relatively rapid uplift makes the mountains towering, the canyons deep, the slope of underground water increases, and various water flows accelerate the development of karst under the condition of large drop.
In addition, regional climate change, precipitation difference, address structure, limestone occurrence, composition and structure, as well as ground slope, vegetation and other factors will also affect karst landform characteristics. For example, in North China, there is relatively little precipitation, karst water is not active, and it is also limestone. Funnels, depressions, towers and other forms on the surface are rare. Underground karst is mainly karst caves, and there are few large underground karst caves. In Guilin area, both steep arc peaks and large caves are distributed in a set of crustal limestone about 3.8 million years ago, which is a kind of limestone formed in the coastal part of the ancient ocean. It has been scoured and scoured by strong seawater, and its porosity and permeability are small, and its corrosion resistance and mechanical strength are greater than those of limestone with more mud, so it can often form steep stone peaks and large caves.
Distribution of karst landforms in China
China's limestone area covers an area of about 6.5438+0.3 million square kilometers, accounting for one-seventh of the total area of the country, and all of them have different degrees of karst landforms.
In addition to the world-famous karst landforms such as Guilin and Yunnan, in East China (including Jiangxi, Anhui, Jiangsu, Zhejiang, Fujian and Shanghai), although the limestone exposed on the surface only accounts for 4.06% (27,900 square kilometers) of the total area, there are still karst landforms in different forms. Karst hills with a relative height of about100-150m and a circular top are developed in northern Jiangsu and northern Anhui. A short cone-shaped peak cluster with the same bottom appeared in Pingxiang-Yichun area of Jiangxi Province. Tianmu Mountain in Zhejiang, southern Anhui and northwestern Jiangxi is a karst mountain area with a few caves. The strongest karst development is in Longyan and Sanming in southwest Fujian, where there are not only peak forests, peak hills and karst caves, but also hundreds of meters long karst underground rivers.
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Among the 15 provinces in the Yangtze River valley of China, the exposed area of limestone in Sichuan Province is 128062 square kilometers, which is much larger than other areas. The karst in the west of Yichang, Hubei Province is developed, widely distributed, complete in form and beautiful in landscape. Karst canyons (basins) are the main areas in Yunnan-Guizhou Plateau, western Hubei, central Hunan, western Hunan and northeastern Guangxi. Alpine karst is mainly distributed in western Sichuan, eastern Qinghai-Tibet Plateau and Hengduan Mountain area in Heyuan area. Under the influence of freezing weathering and ice source glaciers, limestone karst is weak, and the surface landscape is characterized by alpine landforms, mostly alpine land with an altitude of 4000-6000 meters. Karst is mostly distributed in the periphery of Sichuan Basin, that is, Qinling, Minshan, Longmen, Daliangshan, Jinping and Wulianfeng, with a total area of 3,500m. There are large caves and underground rivers exposed in mountainous depressions; The average elevation of mountain karst is 1000- 1500m, which is distributed in northeast Guizhou, western Hubei, western Hunan and eastern Sichuan. The long-term hot and humid climate and neotectonic movement since the Cenozoic era have made the karst in this area develop in a wide range and in all forms, including both peak forest karst landscape, peak cluster canyons and valleys. Peak forest karst at an altitude of 300-800 meters is widely distributed in southern Hunan and northeastern Guangxi, located in the west of Nanling Mountains, especially represented by Guilin peak forest landform. There are tall and straight peaks, numerous peaks, various forms of karst dotted with underground caves. There are stalactites, stalagmites, stone curtains, stone curtains, stone waterfalls, stone grapes, stone flowers and flowing water all over the cave, which complement each other with the beautiful mountains and forests on the surface, forming a wonderful work of "strange peaks, strange caves and beautiful stones" on the land of the motherland.
The geological and geographical conditions in Northeast China are not conducive to the development of karst landforms, but the limestone of 70,920 square kilometers there is the foundation of karst development. In some areas in the southeast of Northeast China, a unique coastal karst landscape has been formed due to conditions such as temperature, rainfall, lithology, sea level fluctuation and wave action. In the coastal area at the southern tip of Liaodong Peninsula, there are also clusters of stone buds about 10 meters high, which are also the products of karst.
Kunlun Mountain spans the western part of China, stretching for 2,500 kilometers from east to west. After years of investigation by scientific workers, a large area of ancient karst landforms that cannot be formed by freezing weathering of modern mountains has been discovered in the middle branch of East Kunlun Mountain. According to textual research, this is the product of the thermal effect caused by the strong uplift of the Qinghai-Tibet Plateau and the influence of the Indian Ocean monsoon on this area. Although these ancient karst landforms were greatly transformed and destroyed by intense late tectonic movement and cold and frozen climate, early and late ancient karst peak forests, stone buds, karst caves and dissolution cracks can still be clearly seen in the upper part of the mountain at an altitude of 4700-5300m and the lower part of the mountain at an altitude of 4300-4800m. They echo the ancient karst landform of Tanggula Mountain in the south of this area and become a history of great changes.
Karst landform and human beings
Humans have had an indissoluble bond with karst since ancient times. In ancient times, caves were often the habitat of primitive people. Famous Peking man, Neanderthal fossils and fire remains were found in the caves. The ancestors of Zhupi Rock in Guangxi also lived in caves for a long time, leaving a rich "cave culture".
China is the first country to study karst in the world. The word "stalactite" was put forward in Shennong's Classic of Materia Medica in the Western Han Dynasty, and it was divided in detail. Great progress has been made in the study of the Three Kingdoms, the Song Dynasty and the Ming Dynasty. Xu Xiake, a geographer in Ming Dynasty, braved hardships and dangers, and made a systematic survey of the vast limestone distribution area in southern China for three consecutive years (A.D. 1637- 1639), and explored more than 300 caves. He was the greatest cave explorer in ancient China.
The caves found in China are often rich in minerals and groundwater, which can meet the needs of industrial and agricultural production. At the same time, these caves will also suspend buildings and roads, and this sudden flood and sediment will often cause harm to the project, so we should pay attention to it in our daily work and life.
Karst landforms have peculiar forms on the surface and underground. The stone peaks and buds in the plains and basins give people a sense of forests and bamboo shoots. Dissolution and chemical deposition make the shapes of peaks more peculiar and changeable, including continuous peak clusters and high and sharp arc peaks, divided peak forests and slender cylindrical arc peaks, which give people a strange imagination and are called "changing modeling landforms". It is the strong observability and distinctive features of karst that make it a unique tourism resource. Huangguoshu, which grew on the edge of karst plateau, was fascinated by the waterfall 66 meters long and 50 meters wide. The wide underground cave makes the viewer feel mysterious and amazed, and produces an unfathomable magical artistic conception, which is called' magical underground palace'.
Due to various reasons and conditions, there are still a large number of deep and long caves that have not been studied or discovered in China, which can be developed as places for exploration and investigation to meet the needs of Chinese and foreign explorers, and steep peak forests are ideal places for rock climbing.