Landforms Made by Running Water
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Landforms Made by Running Water
• Fluvial Processes and Landforms
• Slope Erosion • The Work of Streams • Stream Gradation • Fluvial Processes in an Arid Climate
Fluvial Processes and Landforms
fluvial landforms are shaped by the fluvial processes of overland flow and stream flow. Wherever rain falls, these processes act to create erosional and depositional landforms
Figure 16.1, p. 547
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Slope Erosion
soil erosion occurs when overland flow moves soil particles down-slope erosion is greatest on bare slopes of fine particles, carving rills and gullies a vegetation cover greatly reduces soil erosion
Figure 16.3, p. 548
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Slope Erosion
soil particles moved down-slope eventually reach the base of the slope, where they come to rest and accumulate in a thickening layer termed colluvium if not deposited as colluvium, sediment carried by overland flow eventually reaches a stream, is carried farther down-valley and may accumulate as alluvium (a stream-laid sediment deposit).
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The Work of Streams
streams erode their beds and banks by hydraulic action, abrasion, and corrosion abrasion by stones on a bedrock riverbed can create deep depressions known as potholes
Figure 16.6, p. 551
The Work of Streams
streams carry dissolved matter, sediment in suspension, and a bed load of larger particles bumped and rolled along the bottom
a stream’s capacity to carry sediment increases sharply with its velocity
Figure 16.7, p. 551
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Stream Gradation
over time, a stream develops a graded profile in which the gradient is just sufficient to carry the average annual load of water and sediment produced by its drainage basin
Figure 16.9, p. 553
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Niagara Falls
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Stream Gradation
Evolution of a graded stream
(a) stream established on a land surface dominated by landforms of recent tectonic activity
(a)
(b)
(b) gradation in progress the lakes and marshes drained, the gorge is deepening, and the tributary valleys are extending (c) graded profile attained – floodplain development is beginning, and the widening of the valley is in progress (d) Floodplain widened to accommodate meanders
(c)
(d)
Figure 16.10, p. 554
Stream Gradation
evolution of side slopes: following stream gradation, the valley walls become gentler in slope, and the bedrock is covered by soil and weathered rock
Figure 16.13, p. 556
Stream Gradation
alluvial terraces form when an aggrading river loses its sediment input and begins degrading its bed, leaving terraces behind as it cuts deeper into its sediment-filled valley
an alluvial river, with its low gradient and broad floodplain, creates characteristic landforms including bluffs, meanders, cutoffs, ox-bow lakes, and natural levees
Figure 16.19, p. 559
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Stream Gradation
as a flood plain develops it widens over time creating a flat valley floor where the river meanders back and forth (ALLUVIAL MEANDERS) (on the inside of each bend – point bar deposition, on the outside of each bend – erosion)
Figure 16.12, p. 555
Stream Gradation
accelerated soil erosion and glacial activity can increase the amount of sediment brought to a river system, causing aggradation and the development of braided streams and river segments
Figure 16.18, p. 559
Stream Gradation
floodplain landforms of an alluvial river as meanders wander downriver, they create a variety of landforms, including ox-bow lakes, cutoffs, and natural levees
Figure 16.21, p. 563
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Stream Gradation
where rapid uplift causes meandering rivers to cut deeply into bedrock, entrenched meanders are formed
Figure 16.22, p. 563
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Stream Gradation
the geographic cycle traces the fate of rivers and fluvial landforms from an initial uplift creating steep slopes and canyons to a final low, gently rolling surface called a peneplain
the equilibrium approach sees fluvial landforms as reflecting a balance between processes of uplift and denudation acting on rocks of varying resistance to erosion uplift and rejuvenation
Figure 16.19, p. 559
Fluvial Processes in an Arid Climate
stream water flow to ground water In humid regions - a stream channel receives ground water through seepage
in arid regions stream water seeps out of the channel and into the water table below
Figure 16.28, p. 567
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Fluvial Processes in an Arid Climate
although rain is infrequent in desert environments, running water shapes desert landforms with great effectiveness because of the lack of vegetation cover
Fluvial Processes in an Arid Climate
alluvial fans are common features of arid landscapes they occur where streams discharge water and sediment from a narrow canyon or gorge onto an adjacent plain
Figure 16.29, p. 568
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Fluvial Processes in an Arid Climate
landforms of mountainous deserts include alluvial fans, dry lakes or playas, and pediments—rock platforms veneered with alluvium
Figure 16.31, p. 569
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Yangtze River, China
Yangtze River Dam, China