Under the action of rivers, the formation and development of the landform go through the stages of infancy, manhood and old age. Later, the area will experience tectonic uplift again, and the landform evolution will repeat the theory of the above process.It is also called landform transmigration theory and geography transmigration theory.In 1889, by WM. Davis proposed.He believes that landform is a function of structure, process (referring to the process of various external forces) and stage (referring to the development stage).
Chinese name
Erosion cycle theory
Geomorphic transmigration theory
The doctrine of childhood, manhood, and old age
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By the United StatesW. M. DavisIt was proposed in 1889
childhood
The river cuts down rapidly and the valley is deep and narrow
It refers to the surface under the action of rivers,landformsThe theory that the formation and development go through infancy, manhood and old age is also called landform transmigration theory and geographical transmigration theory.By the United StatesW. M. DavisIt was proposed in 1889.He believes that landform is a function of structure, process (referring to the process of various external forces) and stage (referring to the development stage), and first assumes that there is a land lifted from the seabed due to tectonic movement. Due to the rapid lifting, the ground is immediately eroded, and the original low terrain becomes high mountains, deep valleys, and steep slopes;Then, the tectonic movement was stable for a long time, and the highland was eroded low,river valleyGradually wide and shallow, gentle slope is popular again;Eventually, the whole ground became a plain terrain with only slight fluctuations, which Davis called peneplain.This is a geomorphic cycle, or erosion cycle, geographical cycle.Later, the area experienced tectonic uplift again, followed by stability, and its geomorphic evolution repeated the above process, that is, it experienced another cycle.Davis vividly named the different stages of the above process as childhood, manhood and old age.
Geomorphic development process
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childhood
Erosion cycle theory
The river cuts down rapidly, the valley is deep and narrow, and the valley slope is steep, close to 30 ° or more.Weathering and landslide also occur on steep slopes, but the river is mainly cut, so the river valley is similar to a "V" shape for a long time. In the whole childhood, most of the original ground remains in the section between rivers. As time goes by, the scope of the original ground gradually shrinks due to the erosion and retreat of the main and tributary valley slopes and the headwater erosion of the riverRiver profileIt is very irregular. There are often waterfalls and water drops at the exposed hard rock layer on the riverbed.Davies called this river profile as non-uniform planation profile.
Manhood
With the downcutting of the river, the longitudinal profile of the river gradually becomes a gentle concave curveRiver DatumApproaching.If it is a river entering the sea, its datum level is the sea surface.Davies called this river longitudinal profile a planation longitudinal profile, or a balanced longitudinal profile, because he assumed that the energy of the river was just consumed in the movement of the river water and sediment.As the downcutting erosion of the river slows down to a standstill, the side erosion of the river and the denudation and retreat of the valley slope are relatively strengthened, so the valley is widened, the original ground of the original inter river section is also denuded and no longer exists, and the new inter river area is gradually reduced.
Senile period
Erosion cycle theory
The riverbed gradient continues to decrease, and the valley slope continues to slow, but at a slow speed.Finally, the whole terrain becomes a slightly undulating peneplain.Davies took the Maunalnock Mountain on the New England peneplain as an example, pointing out that there may still be some small highlands left on the peneplain, called the Maunalnock landform.
Water erosion is the most common exogenic process, soFluviationThe next erosion cycle is called normal erosion cycle.
Theoretical evaluation
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Davis's theory was popular from the end of the 19th century to the beginning of the 20th century, which greatly promotedGeomorphologyIt is one of the important signs of the formation of geomorphology.However, some geomorphologists hold different views:
Erosion cycle theory
① Some scholarsModern tectonic movementBased on the research results of sea level changes, it is pointed out that the crustal movement cannot be all temporary and sudden rise, followed by long-term stability.Moreover, the sea surface, as the base level, is not stable for a long time.Davis and his supporters believe that in some cases, geomorphic development can complete a cycle, so there are peneplain landforms in many parts of the world;Sometimes the terrain development is interrupted by a new rise before it has completed a cycle, which will lead to the overlapping of terrain in multiple development stages.
② Some scholars believe that the exogenic force is not only water erosion, but also glacier erosion, freezing weathering and wind erosion (seeErosion)。Even water erosion is different in humid and rainy areas with dense vegetation and arid areas with sparse vegetation.In the humid area, there are many linear flows, and the landform is developed with springs, which can produce what Davis called the peneplain.In arid areas, there are many sheet or braided water flows, and the erosion undercutting effect is weak. Under the erosion of gravity erosion or sheet water flow, the hillside retreats in parallel, creating a vast piedmont denudation plain, so that sometimes there are some "island mountains" left on this plain. This process is called piedmont leveling erosion cycle.
③L.C. Peltier put forward the theory of the formation of local planation surface in 1950, that is, the theory of the cycle of freezing erosion on the ice margin.He pointed out that in today's high latitude areas or areas with strong frost weathering at the top of mountains, the rock debris generated by the frost weathering was brought to the slope toe of the highland by soil flow during the thawing period, so that the highland was gradually flattened.This kind of planation exists in some areas.
④ As forPlanation planeThe origin of the landform and the existence of erosion cycles in the long history of geological development are still uncertain.
