Rivers-Fluvial Landforms & Processes

Lucy Monger
Flashcards by Lucy Monger, updated more than 1 year ago
Lucy Monger
Created by Lucy Monger over 6 years ago


A Level Geography AS (Rivers) Flashcards on Rivers-Fluvial Landforms & Processes, created by Lucy Monger on 11/26/2014.

Resource summary

Question Answer
Physical Weathering Freeze thaw Salt Crystal Growth Pressure Release
Chemical Weathering Hydrolysis Hydration Oxidation Carbonation Solution
Biological Weathering Involves both Physical and Chemical weathering
Slides Detached block remains large until the bottom of the slope where it is broken down on impact
Sheetwash -The unchannelled flow of water over a soil surface -Divided into areas of high and low velocities
In Situ Without any lateral movement (on the spot)
Pools The deep part of the river located on the outer bend of a meander
Riffles The ridges- often formed of gravel- found in the straight part of a river between two meanders
Cavitation The explosion of air in joints and cracks as a result of air at very high pressure
Hydraulic Radius Cross-sectional area of a river divided by the wetted perimeter
Wetted Perimeter Total length of the bed and base of the river channel in contact with water in the river
Suspension Smallest particles (silt/clay) carried in suspended load -important during times of flooding
Saltation Large particles (sands/gravels) transported in a series of bounces as the salted load
Traction Larger particles (pebbles) Shunted along the bed
Solution In areas of calcareous (mostly or partly composed of calcium carbonate) rock, material carried in solution
Sediment Yield The amount of material (debris) carried away by water
Entrainment Picking up particles from the ground/ river bed
Unconsolidated Rocks Loose, broken material that is often easily eroded
Consolidated Rocks Solid rocks or sediment that have been bonded together by a sedimentary cement
What is a Pothole? How are Potholes formed? -A pothole is a hole in the base of the stream of the river -Formed through abrasion by pebbles held up by turbulent flow in the eddies of the stream
What is an Eddy? The swirling of a fluid and the reverse current created when the fluid flows past an obstacle
Why are Meanders formed? When stream velocity has increased and the load is finer, in relatively straight channels, meanders develop as this is the only way the stream can use up the energy it now possesses equally throughout the channel reach
Thalweg The line of maximum velocity in the river
Helicoidal Flow A corkscrew-like motion that occurs in a meander
River Cliffs The steep-sided slopes on the outer ben of a meander
Slip-off Slope The gentle slope deposited on the inner bend of a meander
Bankfull Stage Where the variables of the river (depth, width, velocity) of a river are unable to cope with additional water
Oxbow Lake
Braided Channels
How is an Oxbow lake formed? -Lateral erosion (caused by centfrifugal forces) is concentrated on the outer, deeper bank of the meander -During flooding erosion increases causing the river to break through and create a new steeper channel, the old meander is eventually closed off by deposition to form an oxbow lake
When do Braided channels occur? -When the river separates into multiple small interlocking channels -Channel is now highly unstable and constantly changes form -Occurs when the river capacity can't transport its load in a single channel, be straight or meandering
What are Floodplains? -Increased discharge due to heavy precipitation can lead to a bankfull stage -Channel variables become unable to cope and river spills out into surrounding areas -Repeated flooding leads to build up of alluvium and forms the floodplain -Also created by bluffs (steep banks or cliffs)
What are Levees? -Raised ridges that run parallel to the edge of the channel and forms the repeated flooding of a river -Rivers flooding causes its velocity to drop as the floodwaters spill out -Heaviest and coarsest sediment are the first to be deposited and will build up over time
Alluvium Fine sediment of silt and clay transported in suspension (very fertile)
Flocculation The process in which clay and silt particles combine when fresh water mixes with the salt water
For Deltas to form a river needs to... -Carry a large volume of sediment -Enter a still body of water (sea/lake) IF STRONG CURRENTS SEDIMENT WOULD BE CARRIED BY LONGHSHORE DRIFT
How are Deltas formed? -Deposition increases if the water is salty; causes salt particles to group together and they become heavier -Vegetation increases the rate of deposition by slowing down the water -Coarser material deposited first and finest last
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