1GB2 4b River Processes Flashcards Preview

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Flashcards in 1GB2 4b River Processes Deck (14)
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1

Saltation

Smaller stones or pebbles are picked up and then dropped again. This results in a ‘skipping’ motion.

2

Traction

Large stones are dragged along by traction

3

Solution

Dissolved chemicals are carried along in solution, invisible to the eye

4

Suspension

Tiny particles of sediment are carried in suspension in the river’s current.

5

Abrasion

Where sand and pebbles are dragged along the river bed, or know into it by saltation, wearing away the bed.

6

Attrition

Where coke and stones wear each other away as they know together

7

Hydraulic action

Where fast-flowing water is forced into cracks, breaking up the bank over time

8

Solution

Where alkaline rocks, such as limestone, are dissolved by acidic rainwater

9

How are waterfalls formed?

Waterfalls occur when a river crosses a bed of mor resistant rock (hard rock).
Erosion of the less resistant rock (soft rock) underneath continues- undercutting the hard rock above it. The river’s energy creates a hollow at the foot of the water known as a plunge pool
The less resistant rock beneath is eroded more rapidly by abrasion and hydraulic action. This creates a ledge, which overhangs and collapses.
The waterfall takes up a new position, leaving a step valley or gorge.

10

Biological weathering

Small cracks in rocks allow plant roots to penetrate in search of water and nutrients. As they grow, root cells force the cracks apart, widening them and breaking the rock into pieces.

11

Physical weathering

Physical weathering occurs when physical force breaks rock into pieces. In winter, cracks in the limestone rock fill with rain. This freezes, expanding in volume by 10% and widening cracks so that more water gets in. This process is known as freeze-thaw. If repeated often enough, pieces of rock break away, becoming scree at the base of the cliff

12

Chemical weathering

It is any chemical change or decay of solid rock. Rainwater mixes with atmospheric gases, e.g. CO2, to form weak acids which dissolve alkaline rocks such as limestone.

13

Mass movement

All process that cause rock material to move downslope under gravity .

14

Rapid mass movement

Such as landslides and mudflows
These are less common in the uk, though they do occur on railways cuttings and along cliff coastlines