Running Water Erosion and Weathering
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Transcript of Running Water Erosion and Weathering
Running WaterErosion and Weathering
The hydrologic cycle is a summary of the circulation of Earth’s water supply
Processes involved in the hydrologic cycle
PrecipitationEvaporationInfiltrationRunoffTranspiration
Evapotranspiration
Stream channel – long, narrow depression eroded by the stream into rock or sedimentStream bank – sides of channel
Stream bed – bottom of channel
During flooding, waters overflow banks onto the flood plain of valley floor
V- shaped or broad channels
Factors affecting stream erosion and deposition
Velocity – primary influenceControlled by GradientChannel shapeChannel roughness
Discharge – lesser influence
Velocity – distance water travels in a stream per unit time
Moderately fast stream – 5 km per hour (3 mi/hr)
Fast stream (flood) – 25 km per hour (15 mi/hr)Velocity is the key to stream’s ability to
erode, transport, and deposit sediments.Maximum velocity achieved in middle of
channelOutside of curve – centrifugal force – faster
velocities - erosionInside of curve – slower velocity - deposition
Stream channel – long, narrow depression eroded by the stream into rock or sedimentStream bank – sides of channel
Stream bed – bottom of channel
During flooding, waters overflow banks onto the flood plain of valley floor
V- shaped or broad channels
Factors affecting stream erosion and deposition
Velocity – primary influenceControlled by GradientChannel shapeChannel roughness
Discharge – lesser influence
Velocity – distance water travels in a stream per unit time
Moderately fast stream – 5 km per hour (3 mi/hr)
Fast stream (flood) – 25 km per hour (15 mi/hr)Velocity is the key to stream’s ability to
erode, transport, and deposit sediments.Maximum velocity achieved in middle of
channelOutside of curve – centrifugal force – faster
velocities - erosionInside of curve – slower velocity - deposition
Flood PlainsBroad strip of land built up by sedimentation on either side of a stream channel
Flooding covers land with water suspended with silt and clay, which gets deposited as flood waters recedes and slow down, flat smooth plain of sediment
Series of floods may deposit sediment in low ridges near banks creating a natural levee
Formation of natural levees by repeated flooding
Alluvial fansDevelop where a high-gradient stream leaves a narrow valley
Slopes outward in a broad arc – depositing sediment as velocity slows down
Formed in dry climates where streams don’t reach a body of water
DeltasForms when a stream enters an ocean or lake (mouth of stream)
Shape of triangle (Greek symbol delta Δ)
Consists of three types of bedsForeset beds- main body, angledTopset beds- next layer, horizontal fine-grained
Bottomset beds – in front of foreset, very fine-grained clays
Stream developmentDowncutting – process of deepening of a
valley by erosion of a stream bedLimit of downcutting – base level –
theoretical limit of erosion of earth’s surfaceV-shaped valleysSlot canyonsSlow process over timeFaster process – mass wasting – times of
floods
Lateral Erosion – widening of channel in flood plain – lateral motion
Headward Erosion – lengthening of channel by erosion at mouth
Stream terraces – step-like landforms, downcutting into new flood plains
Incised meanders – regional uplift of land
Superposed streams – erosion through the mountain range