Examples are given to illustrate the features of granite landform, Danxia landform, karst landform and coastal landform.
The landscape map of granite is the general name of peak-forest-like hills composed of granite rock mass and spherical stone eggs or steamed bread-like mounds. The former is dominated by granite, with steep rock structure and terrain, exposed rocks, strong weathering and denudation along joints and faults, and flowing water cutting, forming strange peaks and deep valleys. The latter is composed of dome-shaped granite with red weathering crust and thickness of 10 ~ 80m. After the weathering crust is peeled off, spherical stone eggs or steamed bread-shaped rock mounds are exposed, and the terrain is round. The development of granite landform is deeply influenced by lithology. On the one hand, because of its massive structure, hard and dense, strong corrosion resistance, it often forms steep mountains; On the other hand, due to the loose and sandy weathering crust, the original rock under it is impermeable to water, which is easy to produce surface scattered flow and rainstorm flow, resulting in serious soil erosion; Because of rich joints, spherical weathering occurs; Surface water and groundwater move along joints, gradually forming dense valleys and valleys; Where joints are staggered or fractured, several small basins are often formed; The number and form of joints determine the shape of the hillside. In the area with dense joints, gravity collapse is obvious and vertical cliffs appear. Layered weathering and erosion keep the slope angle unchanged, while spherical weathering and erosion make the slope rounded. Weathering along the joints can penetrate deep into the rock mass and form a thick red weathering crust. In addition, the rock mass structure also has an influence on the granite landform.
[Edit this paragraph] Granite distribution in China.
Granite mountains in China are widely distributed, concentrated in the Yunnan-Guizhou Plateau and the second and third terrain steps east of Yanshan Mountains. It is mainly in the middle and low hills below 2500 meters above sea level, and some other mountains are also distributed. Many famous mountains in China, such as Daxinganling and Xiaoxing 'anling in the northeast, Qianshan, Yiwulu and Fenghuang in Liaoning, Taishan, Laoshan and Yishan in Shandong, Huashan and Taibai in Shaanxi, Huangshan, Jiuhua and Tianzhu in Anhui, Moganshan, Putuo and Tiantai in Zhejiang, Hengshan and Jiuyi in Hunan and Jiangxi. Lingyan Mountain and Tianping Mountain in Jiangsu, Panshan Mountain in Tianjin, Yunmeng Mountain in Beijing, Laoling Mountain in Hebei, Helan Mountain in Ningxia, Qilian Mountain in Gansu, Gongga Mountain in Sichuan, Dazhou Island in Hainan, Tongguling Mountain, Qixingling Mountain and Wuzhishan are almost or mostly made of granite. Many of them have become national scenic spots and nature reserves.
Danxia landform
Danxia landform is a type of red bed landform, which developed in the red continental glutenite stratum of the Middle-Upper Cretaceous, and was formed by flowing water erosion, dissolution and gravity collapse, such as Chibi, Fangshan, Shibi, Shifeng, Shizhu, Gully, Stone Lane and Cave. At present, it is defined as "the continental red bed landform with steep cliffs is called Danxia landform [1]".
Danxia landform belongs to red bed landform and is a horizontal structural landform. Refers to isolated peaks and steep rocks formed by long-term weathering and stripping of red sandstone and flowing water erosion. It is the general name of all kinds of Danxia peaks developed along vertical joints in extremely thick red sandstone and conglomerate layers. It is mainly developed in the horizontal or gently inclined red strata from Jurassic to Tertiary. This landform is the most typical in Danxia Mountain, Shaoguan City, northern Guangdong Province, so it is called Danxia landform.
[Edit this paragraph] Discovery and naming
1928, Feng Jinglan and others discovered Danxia landform in Renhua County, northern Guangdong Province, and named the red gravel stratum that formed Danxia landform as Danxia stratum. Since then, many people have expounded this, such as: Chen, Wu Shangshi, Zeng, etc. It is now defined as "the continental red bed landform with steep cliffs is called Danxia landform".
karst landform
The floorboard of the surface and underground forms formed by dissolving soluble rocks with water. Also known as karst landform. The action of water on soluble rocks is called karstification. It is dominated by dissolution, and also includes mechanical erosion processes such as running water erosion, latent erosion and collapse. This effect and its phenomenon are collectively called karst. Karst is the place name of carbonate plateau in Istra Peninsula in northwest Yugoslavia, and it is called Kras locally, which means the place where rocks are exposed. Modern karst research originated in this area, hence its name.
Karst landforms are distributed in soluble rock areas all over the world. There are three types of soluble rocks: ① carbonate rocks (limestone, dolomite, marl, etc. ). ② Sulfate rock (gypsum, anhydrite, mirabilite). (3) Halide rocks (potassium, sodium, magnesium salt rocks, etc. ). The total area is 5 1× 106 square kilometers, accounting for 10% of the total area of the earth. Karst landform develops from tropical zone to cold zone, and from mainland to island. Famous areas include China, Guangxi, Yunnan, Guizhou, northern Vietnam, Dunac Alps in Yugoslavia, Alps at the junction of Italy and Austria, French Central Plateau, Russian Urals, southern Australia, Kentucky and Indiana in the United States, Cuba and Jamaica. The karst landforms in China are widely distributed and cover a large area. It is mainly distributed in the carbonate outcropping area, covering an area of about 9 1- 1.3 million square kilometers. Among them, Guangxi, Guizhou, Yunnan, and eastern Qinghai (namely Yunnan-Guizhou Plateau) are the largest karst areas in the world. Tibet and some northern areas are also distributed.
Karst can be divided into many different types. According to the exposure conditions, it can be divided into bare karst, covered karst and buried karst. According to climatic zones, it can be divided into tropical karst, subtropical karst, temperate karst, cold karst and arid karst. According to lithology, it can be divided into limestone karst, dolomite karst, gypsum karst and salt karst. In addition, there are different divisions according to altitude, development degree, hydrological characteristics and formation period. Phenomena similar to karst in form due to other differences are collectively called pseudo-karst, including clastic karst, loess and clay karst, hot lava karst and lava karst in volcanic rock area. They are not composed of soluble rocks, which are essentially different from karst.
Karst landforms are most developed in carbonate strata distribution areas. Rock outcrops and strange peaks abound in this area. The common karst landforms on the surface include karst positive landform such as stone bud, stone forest, peak forest and karst hills, and karst negative landforms such as karst gullies, sinkholes, blind valleys, dry valleys and karst depressions. Underground karst landforms include karst caves, underground rivers and underground lakes. As well as the karst landforms closely related to the surface and underground, such as shafts, bud caves and Tianshengqiao.
Karst research has important theoretical and practical significance. There are many unfavorable factors to be overcome and prevented in karst areas, and there are also many favorable factors to be developed and utilized. Karst mineral springs and hot springs are rich in beneficial elements and gas and have medical value. Karst caves and ancient karst surfaces are rich in sedimentary minerals, and ancient karst buried hill is a good oil and gas reservoir structure. The grotesque caves in karst areas, rivers with alternating light and dark, and clear karst springs are all good tourism resources.
Underground river formed by flowing water erosion under karst landform. There are common landforms such as stone buds, gullies, stone forests, funnels, sinkholes, dissolved depressions, inclined valleys, blind valleys and peak forests on the surface. Underground, there are caves, underground rivers and other cave systems, as well as stalactites, stalagmites, stone pillars and stone waterfalls in caves. Underground caves and karst deposits, such as Jiutian Cave in Sangzhi County, Zhangjiajie, Hunan Province, have been listed as the first cave in Asia, and Huanglong Cave has been listed as a part of Wulingyuan in Zhangjiajie, a world natural heritage, a world geological park and the first batch of national 5A tourist areas. It is the topographic representative of underground karst in Zhangjiajie, in which karst landforms account for about 40% of the city's area. The distribution area of carbonate rocks is about 6.5438+300,000 km2, and karst landforms are widely distributed. In China, they are mainly distributed in Guangxi, Guizhou, Yunnan, Hunan and other provinces, such as Guilin landscape in Guangxi and Lunan Stone Forest in Yunnan.
The formation of karst caves is the result of long-term dissolution of groundwater in limestone areas. The main component of limestone is calcium carbonate (CaCO3), which reacts with carbon dioxide in the presence of water to generate calcium bicarbonate [Ca(HCO3)2], which is soluble in water, so it forms a cavity and gradually expands. This phenomenon is most typical in the karst plateau along the Adriatic Sea in southern Europe, so this terrain in limestone area is often called karst terrain.
According to its development and evolution, karst landform can be divided into the following six types. 1) Surface water dissolves along the joint surface or fracture surface in limestone, forming a karst ditch (or karst trough), and the limestone originally distributed in layers is divided into stone pillars or stalagmites by the karst ditch. 2) Surface water permeates and dissolves downward along limestone cracks, and when the depth exceeds 100 meters, a sinkhole is formed ... 3) The groundwater falling from the sinkhole flows laterally to the aquifer, forming a karst cave. 4) With the formation of underground caves, the surface collapses, and those with large collapse depth and small area are called collapse funnels, while those with small depth and large area are called collapse ponds. 5) Long-term joint action of groundwater dissolution and collapse forms slopes and valleys and natural bridges. 6) When the ground rises, the original caves and underground rivers are taken out of the ground and turned into dry valleys and stone forests, and the dissolution of groundwater continues under the old caves and underground rivers. The stone forest in Lunan, Yunnan Province is the product of the first stage (ditch-dissolving stage), and the natural scenery here is particularly charming because of the touching legend of Ashima girl. Elephant trunk mountain in Guilin was formed when the primitive underground river was exposed to the surface. In Guangxi, you can often see this kind of cave exposed to the surface, commonly known as "fairy mirror" or "fairy mirror".
Because of its unique geomorphological characteristics, karst landforms are often easy to "produce" different types of scenic spots.
coastal landform
The general name of all kinds of landforms formed by tectonic movement, seawater dynamics, biological action and climate factors. The alternation of Quaternary Glacial Period and Interglacial Period caused the sea level to rise and fall, and the coast was constantly changing. 6000 ~ 7000 years ago, the sea level rose to the height equivalent to modern sea level, which constituted the basic outline of modern coast and formed various coastal landforms.
In the process of shaping coastal landforms, tectonic movement laid the foundation. On this basis, wave action, tidal action, biological action and climate factors have shaped many complex coastal shapes. Wave action is the most active dynamic factor in shaping coastal landforms. Offshore waves have great energy. According to theoretical calculation, the wave height is 1m, and the wave with a period of 8 seconds propagates 8× 106 joules per second on the coast stretching 1km. The coast is constantly eroded under the action of waves, and various marine erosion landforms are developed. Debris eroded by sea waves is carried by coastal currents and accumulates in areas with weak input wave energy, forming a variety of accumulation landforms. Tidal current is the main force of sediment transport. When the actual sediment concentration of tidal current is lower than its sediment carrying capacity, it can continue to scour the seabed; When the actual sediment concentration exceeds the sediment carrying capacity, there will be some sediment deposition. In tropical and subtropical waters, there can be coral reef coasts; Mangrove coast can be formed in bays and beaches where salt marsh plants are widely distributed. The reproduction and metabolism of organisms have certain decomposition and destruction effects on coastal rocks. In different climatic zones, with the difference of temperature, precipitation, evaporation and wind speed, the form and intensity of coastal weathering are different, which makes the coastal landform have certain zonality.
According to the basic characteristics of coastal landforms, it can be divided into two categories: coastal erosion landforms and coastal accumulation landform. Erosion landforms refer to various landforms formed by continuous erosion of rocky coasts by waves and tidal currents, mainly including sea caves, sea cliffs, sea platforms and sea pillars. Due to the different composition of coastal materials, the speed of erosion and the degree of landform development are also different. Accumulated landforms are all kinds of landforms formed by the deposition of nearshore materials carried by waves, tidal currents and winds. According to the relationship between the shape of the accumulation body and the coast and its causes, it can be divided into adjacent landform, free landform, closed landform, surrounding landform and coastal landform. According to the material composition and morphology of the coast, it can be divided into sandy coast, muddy coast, delta coast and biological coast.
The world coastline is about 440,000 kilometers long. China's coastline is1.8000 km long, and the island coastline is1.4000 km long. The coastal zone is rich in natural resources, such as minerals, biology, energy and land. This is an important field of human activities. There are industrial cities and seaports everywhere. It is not only a national defense outpost, but also a hub of land and sea transportation and an important base for economic development. It is of great significance to study the coastal landform, master the evolution process of seahorse seal beach and predict the changing trend of the coast for the rational development and utilization of natural resources such as port construction, reclamation, aquaculture, tourism and coastal energy.