downcutting

Information about downcutting

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Several stages of downcutting by the San Juan River in Utah can be identified in this 1927 photo. Remnants of former floodplains stand as terraces above the river's modern level.


Downcutting, also called erosional downcutting or downward erosion or vertical erosion is a geological process that deepens the channel of a stream or valley by removing material from the stream's bed or the valley's floor. How fast downcutting occurs depends on the stream's base level, which is the lowest point to which the stream can erode. Sea level is the ultimate base level, but many streams have a higher "temporary" base level because they empty into another body of water that is above sea level or encounter bedrock that resists erosion. A concurrent process called lateral erosion refers to the widening of a stream channel or valley. When a stream is high above its base level, downcutting will take place faster than lateral erosion; but as the level of the stream approaches its base level, the rate of lateral erosion increases. This is why streams in mountainous areas tend to be narrow and swift, forming V-shaped valleys, while streams in lowland areas tend to be wide and slow-moving, with valleys that are correspondingly wide and flat-bottomed. The term gradient refers to the elevation of a stream relative to its base level. The steeper the gradient, the faster the stream flows. Sometimes geological uplift will increase the gradient of a stream even while the stream downcuts toward its base level, a process called "rejuvenation." This happened in the case of the Colorado River in the western United States, resulting in the process that created the Grand Canyon.

Lake bed downcutting

Lake bed downcutting is the erosion of cohesive material such as clay or glacial till from a shoreline by wave action. When the sand cover is stripped away and the cohesive layer is exposed, cohesive material is lost to the water column. Unlike sand, cohesive material cannot be replenished by natural events such as bluff erosion. This can result in a process called "bluff recession," in which waves erode and carry away the material at the toe of the bluff and cause it to become steeper. When the slope reaches a certain angle, the bluff becomes unstable and fails, causing it to recede inland.

References

Oceanic crust      0-20 Ma
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channel is the physical confine of a river, slough or ocean strait consisting of a bed and banks. See Stream bed.

A channel is also the natural or man-made deeper course through a reef, bar, bay, or any shallow body of water.
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worldwide view.

This article or section deals primarily with the United Kingdom and does not represent a worldwide view of the subject.
Please [ improve this article] or discuss the issue on the talk page.

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geology, a valley is a depression with predominant extent in one direction. A very deep river valley may be called a canyon or gorge.

The terms U-shaped and V-shaped are descriptive terms of geography to characterize the form of valleys.
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The base level of a river or stream is the lowest point to which it can flow, often referred to as the 'mouth' of the river. For large rivers, sea level is usually the base level, but a large river or lake is likewise the base level for tributary streams.
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Erosion is displacement of solids (soil, mud, rock and other particles) usually by the agents of currents such as, wind, water, or ice by downward or down-slope movement in response to gravity or by living organisms (in the case of bioerosion).
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This article or section relies largely or entirely upon a .
Please help [ improve this article] by introducing appropriate of additional sources. ()
This article has been tagged since December 2006.
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For other uses of "Bedrock", see Bedrock (disambiguation).


Bedrock is the native consolidated rock underlying the Earth's surface.
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mountain is a landform that extends above the surrounding terrain in a limited area. A mountain is generally steeper than a hill, but there is no universally accepted standard definition for the height of a mountain or a hill although a mountain usually has an identifiable
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geology, a valley is a depression with predominant extent in one direction. A very deep river valley may be called a canyon or gorge.

The terms U-shaped and V-shaped are descriptive terms of geography to characterize the form of valleys.
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In physical geography, a lowland is any broad expanse of land with a general low level. The term is thus applied to the landward portion of the upward slope from oceanic depths to continental highlands, to a region of depression in the interior of a mountainous region, to a plain
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Stream gradient is the ratio of drop in a stream per unit distance, usually expressed as feet per mile or meters per kilometer. A high gradient indicates a steep slope and rapid flow of water (ie.
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Tectonic uplift is a geological process most often caused by plate tectonics which increases elevation. The opposite of uplift is subsidence, which results in a decrease in elevation. Uplift may be orogenic or isostatic.
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A river is said to be rejuvenated when the base level that it is flowing down to, is lowered. This can happen by uplift of land, or by a sea or lake that it is flowing into becoming lower.
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Mouth Gulf of California
Basin countries United States, Mexico
Length 2,330 km (1,450 mi)
Source elevation ~2700 m (~9000 ft)

Avg. discharge 620 m³/s (22,000 ft³/s)[1]
Basin area 629,100 km² (242,900 mi²)
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Motto
"In God We Trust"   (since 1956)
"E Pluribus Unum"   ("From Many, One"; Latin, traditional)
Anthem
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Grand Canyon is a colorful steep-sided gorge carved by the Colorado River in the U.S. state of Arizona. It is largely contained within the Grand Canyon National Park — one of the first national parks in the United States.
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lake (from Latin ligacus) is a body of water or other liquid of considerable size contained on a body of land. A vast majority of lakes on Earth are fresh water, and most lie in the Northern Hemisphere at higher latitudes.
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Clay is a naturally occurring material, composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried or fired.
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glacier is a large, slow moving river of ice, formed from compacted layers of snow, that slowly deforms and flows in response to gravity. Glacier ice is the largest reservoir of fresh water on Earth, and second only to oceans as the largest reservoir of total water.
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Till is an unsorted glacial sediment. Glacial drift is a general term for the coarsely graded and extremely heterogeneous sediments of glacial origin. Glacial till is that part of glacial drift which was deposited directly by the glacier.
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Ocean surface waves are surface waves that occur in the upper layer of the ocean. They usually result from wind or geologic effects and may travel thousands of miles before striking land. They range in size from small ripples to huge tsunamis.
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Sand is a granular material made up of fine mineral particles. It is a naturally occurring, finely divided rock.

Sand comprises particles, or granules, ranging in diameter from 0.0625 (or 1⁄16 mm) to 2 millimeters.
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A water column is a conceptual column of water from surface to bottom sediments.[1] This concept is used chiefly for environmental studies evaluating the stratification or mixing (e.g.
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hill is a landform that extends above the surrounding terrain, in a limited area. Hills often have a distinct summit, although in areas with scarp/dip topography a hill may refer to a particular section of scarp slope without a well-defined summit (e.g. Box Hill).
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