Fluvial Morphology: Landforms Made by Running Water
What is the most important geomorphic agent shaping the landscape?
RUNNING WATER Rivers and Streams
What is the work of rivers and streams?
Erosion Transportation Deposition
Fluvial Morphology:Study of Landforms Made by Running WaterFLUVIAL: from the Latin fluvins for ‘running water’ or streamflow
Fig. 17-3, p. 472
The Long Profile of Streams•At their headwaters, the grade of a stream is usually steep. •At Mid-streams, the angle of the grade becomes more gently sloping.• Near the mouth of the stream, the grade becomes almost flat.
Fig. 17-11, p. 480
Stream StagesStream Stages
Streams also show three stagesstages of gradation from the mountains to the sea, with associated erosionalerosional and depositionaldepositional features:
Youth
Maturity
Old Age
Stream Stage 1 - YouthCharacteristics of Youthful Streams
Steep irregular profileWaterfalls, rapids, and plunge poolsRiver is deepening its channel Cutting into bedrockV-shaped cross-section
• The Cycle of Erosion
Youthful stage•headward erosion and •vertical downcutting dominant
• steep stream gradients promote valley deepening
• narrow, V-shaped valleys
1.The channel at upstream point A-B 2.This channel is located in the stream's headwaters. 3.The stream gradient and surrounding topography is quite steep. 4.Stream velocity is at a maximum and cuts a narrow deep channel. 5.The floodplain is minimal as high velocities carry all sizes of load down stream. 6.Stream load is high as the steep gradient provides the energy for extensive erosion7. Producing a V-shaped river valley.
Fig. 17-1a, p. 470
Fig. 17-CO, p. 468
Waterfalls and Rapids
Hard rock layers have not yet been smoothed awayA waterfall is a vertical drop in a streambedRapids are stream sections with extremely strong currents.Both are sites of vigorous erosionPotential Hydro Electric Power
Stream Stage 2 - Mature ValleyCharacteristics of Mature Valley Streams
Valley widening beginsMeandering StreamFloodplains
Fig. 17-21, p. 487
Figure c-d: Stream channel near the middle of a typical stream profile.
•The channel is now leaving the mountainous terrain and entering a landscape that is more gently sloping. •Causes a sudden reduction in the stream's velocity. •The stream adjusts to this change, by depositing most of its coarse stream load onto the floodplain. •The stream also takes on a braided channel form. •These channels are always changing in size, number, and location
Lateral Erosion - Valley Widening Begins Erosion is greatest on the outside bend
Cut-banksDeposition on the inside bendMeanders
Widen the valleyForm cutoffs Create oxbow lakes
Fig. 17-22a, p. 488
Fig. 17-24a, p. 489
Stream Stage 3 - Old AgeCharacteristics of Old Age Streams
Wide Alluvial Valley StageNatural Levees
Depositional featureParallel to the stream channel on both banks
The channel near the mouth of the stream (Figure E-F). Extensive flat floodplain is composed of Deposits from channel meandering. The channel is quite large and U-shaped. Stream discharge is at a maximum and sediment load is generally composed of finer materials.
Fig. 17-26, p. 491
A river cut-off results in a portion of the river isolated from the new channel called an oxbow
Rivers drop their load when they enter the ocean and form a ________?
Deltas Large deposit of alluvial sediment located at the mouth of a stream where it enters a body of standing water.
http://www.youtube.com/watch?v=AjZLAw_lgZ4&feature=related
Fig. 17-27b, p. 491
Deltas are created when the sediment load carried by a stream is deposited because of a sudden reduction in stream velocity.
Mississippi Birdfoot Delta (Source: NASA).
Fig. 17-27a, p. 491
. Some deltas, like the Nile, have a triangular shape
Ganges River DeltaImage taken 2/28/2000 The Ganges River forms an extensive delta where it empties into the Bay of Bengal. The delta is largely covered with a swamp forest known as the Sunderbans, which is home to the Royal Bengal Tiger. The Ganges River Delta can be found on Landsat 7 WRS Path 137 Row 44, center: 23.12, 90.37.
p. 494
Drainage Basins (Watersheds)
Fig. 17-5, p. 475
p. 474
Lake Itasca is a small glacial lake, approximately 1.8 square miles (4.7 km²) in area, in the Lake District of Northwestern Minnesota.
It is the Source[1] of the Mississippi River.
Table 17-1, p. 479
Los Angeles River Now!
2005
http://www.youtube.com/watch?v=ta35C488dnE
http://www.ilike2learn.com/ilike2learn/Rivers/Longest%20Rivers.html
Is this river aggrading or degrading? Is it near the headwaters or the delta?
Is this river aggrading or degrading? Is it near the headwaters or the delta? Aggrading, at the delta
Is this river aggrading or degrading? Is it near the headwaters or the delta?
Is this river aggrading or degrading? Is it near the headwaters or the delta? Graded, near the middle or end of its course.
Missouri River, MO
Is this stream aggrading or degrading? Is it near the headwaters or the delta?
Is this stream aggrading or degrading? Is it near the headwaters or the delta? DEGRADING, NEAR THE HEADWATERS
Canadian Rockies
Stage Landscape Processes
Youthful Steep hillsides,drainage divides
predominant, V-shaped valleys
Headward erosion,stream downcutting –
vertical erosion
Mature Rounded hills, valley walls predominant,
graded streams,broad floodplains
Lateral erosion, streams adjust to
discharge/loadmeandering
Old age Floodplains, ox-bow lakes,deltas and alluvial plains,
very low relief
Deposition, sluggish stream flow,
poor drainage
Fluvial Processes and Landscapes at Different Stream StagesFluvial Processes and Landscapes at Different Stream Stages
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