Running Water Erosion and Weathering
The hydrologic cycle is a summary of the circulation of Earth’s water supply Processes involved in the hydrologic cycle Precipitation Evaporation Infiltration Runoff Transpiration Evapotranspiration
Stream channel – long, narrow depression eroded by the stream into rock or sediment Stream 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 influence Controlled by Gradient Channel shape Channel 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 channel Outside of curve – centrifugal force – faster velocities - erosion Inside of curve – slower velocity - deposition
Stream channel – long, narrow depression eroded by the stream into rock or sediment Stream 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 influence Controlled by Gradient Channel shape Channel 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 channel Outside of curve – centrifugal force – faster velocities - erosion Inside of curve – slower velocity - deposition
Flood Plains Broad 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 fans Develop 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
Deltas Forms when a stream enters an ocean or lake (mouth of stream) Shape of triangle (Greek symbol delta Δ) Consists of three types of beds Foreset beds- main body, angled Topset beds- next layer, horizontal fine-grained Bottomset beds – in front of foreset, very fine-grained clays
Stream development Downcutting – process of deepening of a valley by erosion of a stream bed Limit of downcutting – base level – theoretical limit of erosion of earth’s surface V-shaped valleys Slot canyons Slow process over time Faster 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