Erosional downcutting by the San Juan River in Utah.

Downcutting, also called erosional downcutting or downward 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. Categories: Stub | Colorado rivers | Utah rivers ... Official language(s) English Capital Salt Lake City Largest city Salt Lake City Area  - Total  - Width  - Length  - % water  - Latitude  - Longitude Ranked 13th 219,887 km² 435 km 565 km 3. ... Geology (from Greek γη- (ge-, the earth) and λογος (logos, word, reason)) is the science and study of the Earth, its composition, structure, physical properties, history and the processes that shape it. ... Look up Channel on Wiktionary, the free dictionary In general, channel refers to the path between two endpoints. ... A running stream. ... Fljótsdalur in East-Iceland A valley is a landform, which can range from a few square miles (square kilometers) to hundreds or even thousands of square miles (square kilometers) in area. ... 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. ... Severe soil erosion in a wheat field near Washington State University, USA. Erosion is the displacement of solids (soil, mud, rock, and other particles) by the agents of wind, water, ice, movement in response to gravity, or living organisms (in the case of bioerosion). ... For considerations of sea level change, in particular rise associated with possible global warming, see sea level rise. ... Bedrock is the native consolidated rock underlying the Earths surface. ... Mount McKinley (Denali) in Alaska (USA) has the largest visible base-to-summit elevation difference on Earth. ... A glaciated valley in the Mount Hood Wilderness showing a characteristic U-shape and the broad shoulders Schematic cross section of an quarterny Alpine valley. ... In physical geography, a lowland is any broad expanse of land with a general low level. ... Stream gradient is the ratio of drop in a stream per unit distance, usually expressed as feet per mile or meters per kilometer. ... A tectonic uplift is a geological process most often caused by plate tectonics which increases elevation. ... A river which is said to be rejuvenated when the base level that it is flowing down to, is lowered. ... The Colorado River from the bottom of Marble Canyon, in the Upper Grand Canyon Colorado River in the Grand Canyon from Desert View The Colorado River is a river in the southwestern United States and northwestern Mexico, approximately 1,450 mi (2,330 km) long, draining a part of the... For other Grand Canyons see Grand Canyon (disambiguation). ...

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. A lake is a body of water surrounded by land. ... Quaternary clay in Estonia. ... Aletsch glacier, Switzerland A glacier is a large, long-lasting river of ice that is formed on land and moves in response to gravity. ... This article is about glacial sediments, for other uses see till (disambiguation). ... Categories: Physics stubs | Physical oceanography | Waves ... Patterns in the sand Sand is an example of a class of materials called granular matter. ... The pelagic zone is the part of the open sea or ocean comprising the water column, i. ... This article is about the New Zealand town of Bluff. ...

References

• Black Hawk College: Fluvial Processes II (Physical Geography 102)
• U.S. Army Corps of Engineers: Lake Bed Downcutting