External force action

Geographical noun

The external force action is also called the external force action, which mainly means that the earth surface is affected by gravity and solar energy The effects of, including physical, chemical and biological Weathering ， Hydrodynamic action ， Glaciation ， Wind action , wave and current action, etc.

Generally, the effect of various external forces (weathering, flowing water, glaciers, wind, waves, etc.) on the gradual erosion of the surface uplift is called Denudation ； The destructive effect of flowing water on land is called Erosion 。 In general, the external force is constantly destroying and leveling Internal force action At the same time, these damaged debris materials are transported and piled up in lowlands and oceans.

Chinese name: External force action
Foreign name: exogenic action

Alias: Agent action
Discipline: Geography

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influence factor

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External force action

The strength of external force is closely related to climate factors, because the hydrology, vegetation and other factors affecting the terrain development are controlled by climate conditions. For example, cold glacier covered areas Freeze-thaw Disintegration Glaciation Mainly in arid areas Wind action Dominant, warm and humid Hydrodynamic action Most active. In this sense, not only Weathering crust 、 Residuum Are obviously Zonality The characteristics of, and even the development of terrain, which has always been considered as non zonal factors, to a certain extent reflect the imprint of climate. In particular, the climate can affect the terrain through vegetation and hydrology: vegetation inhibits external forces in areas with dense vegetation and good water and soil conservation Erosion To protect the ground; In areas with sparse vegetation and even bare ground, the erosion intensity of external forces such as water and wind is strengthened.

The main factors determining the climate conditions are temperature and precipitation, and the distribution of temperature and precipitation on the earth has certain rules. Generally speaking, the temperature gradually decreases from the equator to the poles Absolute height The former is called horizontal (latitude) Zonality The latter is called vertical (height) zonality. Precipitation is not completely dependent on latitude and altitude, but also subject to atmospheric circulation And the distribution of land and sea, in detail, even depends on the topographic relief. Therefore, in every Climatic zone Zhongdu has a unique comparative relationship between water and heat Physical weathering And chemical weathering The unique weathering speed, strength of external force and external force Action combination , which will also produce unique Geomorphic assemblage 。 These will be discussed in the following chapters on the types of topographic genesis.

Effect

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In addition, different rocks can show different Topographical features , but sometimes even the same kind of rock climatic conditions It can also form very different topographical forms. Similarly, some rocks with different properties may produce very similar terrain under long-term external force. For example, at the top of a high mountain, Frost weathering The action can make the granite mountain appear steep and sharp peaks; Similarly, under the influence of long-term weathering, many kinds of rocks can also show the round topography commonly seen in granite areas, which is the result of external force.

After weathering and fragmentation, rocks will be transported by gravity, wind, glacier, water and other external forces and accumulated to low-lying places. It is estimated that before liberation, Yellow River From land erosion, transportation, accumulation to the bohai sea The sediment in the Bohai Sea is an average of 1 billion cubic meters every year. If we add the sediment from other rivers and wind, the total will be more than 2 billion to 3 billion cubic meters. If the bottom of the Bohai Sea is stable, it will only take more than 1000 years to fill the Bohai Sea. However, as the bottom of the Bohai Sea has been sinking, the area of the Bohai Sea has shrunk slightly in the historical period (such as Yellow River Estuary The Bohai Sea is still in the process of one side sedimentation and one side accumulation, and the rates of accumulation and sedimentation are not much different, which can be generally balanced with each other.

Weathering: Under the influence of temperature, water and biology, rocks on or near the surface often collapse and break, forming many rock fragments or sand particles of different sizes, which creates conditions for other external forces.

Erosion: often causes the eroded material to leave the original place and form in the original place Erosive landform ； Common erosion landforms include water erosion Wind erosion 、 Glacial erosion 。

Transportation: weathering or erosion products in wind, water, glacier, etc Transport action Next, you can move from one place to another; by Accumulation landform A large amount of material is transported by the development of.

Internal and external forces

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It can be considered as follows: internal External force The effect on the crust is Unity of opposites The internal force attempts to make the distribution of the crustal material tend to be consistent, while the external force attempts to make the undulation of the earth surface tend to be flat. Internal force action It often creates conditions for the action of external forces Denudation Inevitable strengthening; Similarly, joints, cracks and faults generated by internal forces provide a gap for weathering and denudation of external forces Joint development Into various mountains.

From each stage of geological history, sometimes internal forces may dominate, and sometimes external forces may play a major role. However, the long-term and continuous interaction of internal and external forces on the composition of the crust - various rocks has promoted the continuous evolution and development of various terrains on the earth. with Topography of China According to the spatial distribution characteristics of high in the west and low in the east, in terms of internal forces, the western region is dominated by folds and uplifts, Eastern region Mainly settlement and subsidence; In terms of external force, the western region is dominated by denudation, while the eastern region is dominated by sedimentation.

Wind erosion ： Mushroom stone ， Wind erosion column ， Wind eroded depression

Wind accumulation: desert and loess

Water erosion（ physical phenomenon ）: Valley, gully

Water corrosion (chemical phenomenon): Karst terrain

Flow sedimentation: alluvial fan ， Alluvial plain , Estuary Delta

Glacial erosion : Glacier Valley, U-shaped valley ， Angular peak ， Glacial lake

Geological process	Energy source	Form of expression	Overall trend
Internal force action	come from Earth interior , mainly radioactivity Heat generated by element decay 。	⑴ crustal movement ⑵ Magmatic activity ⑶ Metamorphism	Internal force action The general trend is to make the surface become Unevenness , external force The surface undulation tends to be flat. They work at the same time, so the results are often intertwined.
External force action	come from Outside the Earth ， Mainly Solar radiant energy 。	⑴ weathering ⑵ erode ⑶ carry ⑷ Stacking (5) Consolidation diagenesis	-

Glacial deposit ： Moraine plain ， moraine hill ， Moraine lake

Conclusion: In the process of the earth's change for billions of years, the change of terrain is also affected by external forces.

Common landform

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External force action			Formed landform		Distribution area
Weathering			The surface rock is destroyed and debris remains on the surface, forming Weathering crust (Note: soil is evolved from weathering crust)		Common (example: granite Spheroidal weathering ）
Invasion Erosion do use	Wind erosion		Wind erosion and abrasion , forming gobi Wind eroded depression 、 Wind erosion column 、 mushroom rocks 、 Wind eroded castle etc.		Desert area (example: Northwest China Yardang landform )
	flow water Invasion Erosion	erode	The valley bottom and riverbed will be deepened and widened to form a V-shaped valley, and the slope will be broken to form a vertical and horizontal surface of gullies. "Red Desert"“ Rocky desertification ”		Plateau areas where rivers flow (e.g., the Three Gorges of the Yangtze River, the thousands of ravines and waterfalls on the surface of the Loess Plateau)
		corrosion	Karst landforms such as funnel, underground river, karst cave, stone forest and peak forest are formed. The surface is generally rugged and the surface water is easy to leak		The middle and low latitude soluble rock area where the river flows (example: Guilin Scenery 、 Lunan Stone Forest ）
	Glacial erosion		formation Cirque 、 Angular peak 、 U-shaped valley 、 Glaciation plain 、 Glaciation depression (Finland, the country of five Great Lakes and thousands of lakes in North America)		The high mountains and High latitude Region (example: Fjord Norway )
	Wave erosion		formation Marine erosion landform		Coastal area
Transport action	Wind haulage		"Flying sand and rolling stones"		In drought Semiarid region And the coastal area
	Flowing water handling		"Both mud and sand are under control"		It plays an important role in humid and semi humid areas
	Glacial transport		Material migration		Glacial activity area
	Wave transport		Material migration		Coastal area
sink product do use	Glacial deposit		In the process of primary sedimentation, sediment particles are randomly stacked and formed Moraine landform		The high mountains and High latitude region
	Fluvial sedimentation		formation alluvial fan (mountain pass), delta (estuary), alluvial plain (middle and lower reaches)	Those with large particles and large specific gravity deposit first, and those with small particles and small specific gravity deposit later	Mountain passes and middle and lower reaches of rivers (example: Yellow River Delta 、 Gangetic Plains Etc.)
	Wind deposition		Forming sand dunes (static sand dunes, moving sand dunes) and loess deposits at the edge of the desert		Arid inland and adjacent areas (example: Taklimakan Desert , loess in the Loess Plateau)
	Wave deposition		Formation of beach, etc Coastal geomorphology		Coastal zone
Consolidation diagenesis effect			Forming sedimentary rock		universal

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