Unit 1: Topic 3 - Water On The Land Flashcards
Types of Erosion
ENERGY IS NEEDED
ABRASION - The load is carried down the river which constantly hits and scrapes against he river bed, causing material to break off.
ATTRITION - Erosion between rocks and boulder. Rocks knock into each other, reducing them in size. (Load becomes SMALLER and ROUNDER).
HYDRAULIC ACTION - The force of the water when it hits the river bed and banks (e.g. waterfalls)
CHEMICAL SOLUTION - When the acidic water flows over certain rocks such as chalk, forming a solution that becomes part of the river. Calcium carbonate and acidic water in Britain is an example.
Types of Transportation
ENERGY IS NEEDED
TRACTION (BED LOAD) - Carrying large boulders along the river bed which are too heavy to lose contact with the bed.
SALTATION - Moves small rocks by bouncing them along the bed. Lighter loads leave the bed in a hopping motion.
SUSPENSION - Carries very fine materials such as sand within the water so that it floats as the river flows.
SOLUTION - The dissolved load only occurs within limestone and rocks which are soluble. The load is not visible.
Deposition
ENERGY IS LOST.
- The river dumps material that it has been carrying.
- The largest materials are deposited first as they are the heaviest and require the most energy to move.
- The river drops the load when there is a DROP OF SPEED or the AMOUNT OF WATER is REDUCED.
- This usually happens when the gradient changes at a foot of the mountain or when the water enters a lake, or the inside of bends of the river.
The Course of The River
The start of the River is the SOURCE.
> UPPER COURSE
- Traction of heavy boulders (vertical erosion)
- Lots of energy
- Waterfalls and gorges
> MIDDLE COURSE
- Saltation of pebbles and Suspension
- Reduced speed and therefore reduced energy
- River meanders
- Ox-bow lakes
- Wider valleys
- Wider and deeper rivers
> LOWER COURSE
- Saltation, Suspension and Solution
- Least amount of energy, so slowest velocity
- Enter sea (Estuary) - deposition
- Deposition of smallest rocks
Upper Course Features (Waterfalls and Gorges)
Gorges are formed when the soft rock of the waterfall is undercut. The heavy, hard-to-erode rock is left hanging and eventually collapses due to the sheer weight.
The undercut is formed from heavy erosion of HYDRAULIC FORCE pounding into the plunge pool. Moreover, within the plunge pool would create ATTRITION between other rocks, eroding the soft rock away.
This process repeats itself, pulling the waterfall back away from the original position.
> UPPER COURSE ON MAPS
- Multiple sources of water
- Contour lines are close together
- Steep valleys
- Streams join together
> Valley Cross-Section
- Steep sides
- No flood plains
Middle Course Features (Meanders and Ox-bow Lakes)
A river usually is curved, creating a path for water to travel along.
The outside edge of the bend is where the water travels fastest and so more energy, so more erosion is likely to occur there.
The inside of the bend is the slowest path for water, and so less energy and so more deposition will occur there.
This repeatedly occurs until the bends have a greater angle and the river looks like a horse-shoe shape.
The ‘neck of the river closes together, forming a straight river and separates from the horse-shoe.
The flow of least resistance is down the straight river as there is no friction.
The meander is cut off, forming an Ox-bow lake.
> MIDDLE COURSE ON MAPS
- Flat plains (1km)
- River is wider compared to lower down the channel.
> VALLEY CROSS-SECTION
- Small flood plain
Lower Course Features (Flood plains and Levees)
The lower course involves more flooding and deposition of sediments.
In normal conditions, river stays within its channel.
If there is heavy rain, the river overflows and floods the flood plains. Sediments carried from the river deposit onto the flood plains.
Sediments compact to create of fertile flat floodplain. The sediments raise the height of the plain, called levees that decrease flooding.
> LOWER COURSE ON THE MAP
- Irregular land, suggesting lots of deposition occurred here.
- Tidal lines
- Very flat
- Salt marshes
- River runs into the sea
- Mud flats
> VALLEY CROSS-SECTION
- Massive floodplains
HYDROLOGY (Study of Water)
Water Study of
