Running Water Erosion and Weathering

1. Running Water Erosion and Weathering

2. 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

4. 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

6. Factors affecting stream erosion and deposition • Velocity – primary influence • Controlled by • Gradient • Channel shape • Channel roughness • Discharge – lesser influence

7. 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

9. 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

11. Factors affecting stream erosion and deposition • Velocity – primary influence • Controlled by • Gradient • Channel shape • Channel roughness • Discharge – lesser influence

12. 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

14. 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

15. Formation of natural levees by repeated flooding

16. 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

18. 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

22. 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

23. 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