RIVERS: Landforms (produced by erosion) Flashcards
What landforms are produced by erosion? (2)
- V shaped valleys
- Waterfalls and gorges
How is a V shaped valley formed?
Formed by erosion from a river. WEATHERING and MASS MOVEMENT occur on the valley sides while the river erodes the base of the slopes.
How are waterfalls/gorges formed?
RESISTANT rock, underlain by WEAKER rock, is undercut by HYDRAULIC ACTION and abrasion in the process of enlarging the plunge pool at the BASE.
What landforms are produced by deposition? (4)
- Braided channels
- Floodplains
- Levees
- Deltas
How are braided channels formed?
River becomes braided when main channel SEPARATES into number of SMALLER interlocking channels. The channel is now highly UNSTABLE and its form changes CONSTANTLY. Braiding tends to occur when river does NOT have capacity to transport its load in a single channel, straight or meandering.
How are floodplains formed?
INCREASED DISCHARGE as a result of heavy PRECIPITATION or snow melt could lead to the BANK FULL STAGE. The channel variables become UNABLE TO COPE with the ADDITIONAL water and the river SPILLS OUT of the channel, into the surrounding area. REPEATED flooding and deposition leads to the build up of FINE SEDIMENTS and forms a LOW RELIEF feature filling the original river valley floodplains. Consist of FINE SILT and CLAY.
How are levees formed?
RAISED EDGES running parallel to the edge of the channel and formed by REPEATED FLOODING of a river. When river floods, its VELOCITY DROPS as the water spills out of the channel - therefore heaviest and coarsest sediments are the first to be deposited and over time will build up into levees .Consist of SAND and GRAVEL.
How are deltas formed/ what are deltas?
To be formed, a river needs to:
- Carry a large VOLUME of SEDIMENT
- Enter a STILL BODY of water —> e.g. sea/lake
Delta is a LOW-LYING plain or landform that occurs at the MOUTH of a river near where the river flows into another BODY of water.
What landforms are produced by erosion AND deposition?
- Meanders
- Oxbow lakes
What is a meander?
BEND in a river. They are DEEPER on the outside bank and SHALLOWER on the inside bank. CURVED part of a meander (wavelength) is generally 6 to 10 times the WIDTH of the river channel and/or the discharge.
How are oxbow lakes formed?
During times of flooding, erosion INCREASES causing river to BREAK THROUGH and create a new, STEEPER CHANNEL. In time, the OLD meander is CLOSED OFF by deposition to form and Oxbow Lake.
