Rivers (Hydrosphere)

Question 1

• What is ‘hydraulic action’?

Answer 1

➞ the force of the water 🌊
↳ compresses air trapped in the bank 💨
➜ creating an explosive blast 💥
(causing materials to be dislodged)

Question 2

• What is ‘abrasion’?

Answer 2

➞ force of the water 🌊
↳ throws bedload against the banks 🪨
➜ wearing them down

Question 3

• What is ‘solution’?

Answer 3

➞ Acidity of the water 🌊
↳ dissolves the rocks 🧪🪨

Question 4

• What is the formation of a ‘water-fall’?

Answer 4

BEGINNING:
1.) ➞ Waterfalls 🌊
↳ are found where:
* soft rock (e.g. clay - less resistant) 🪨
is beneath
* hard rock (e.g. granite - more resistant) 🪨

MIDDLE (PROCESSES):
2.) ➞ Erosion occurs through:
* ‘hydraulic action’ 🌊
➜ (the force of water compresses air trapped in the bank, creating an explosive blast, causing materials to be dislodged 💥)
* ‘abrasion’
➜ (the force of water throws bedload against the banks, wearing them down 🪨)
* ‘solution’
➜ (acidity in the water dissolves the rocks 🧪)

ENDING (FINAL PROCESSES):
3.) ➞ Overtime,
* the water is able to erode the underlying soft rock more quickly than the hard rock (as it’s weaker)
➜ DIFFERENTIAL EROSION,

4.) ➞ As the soft rock is eroded,
* it forms an OVERHANG of hard rock & a PLUNGE POOL
➜ where the weaker, softer rock is eroded more deeply.

5.) ➞ Overtime, the overhang collapses due to:
* it’s own weight (as it’s unsupported)
* and the effect of gravity
➜ this causes the waterfall to retreat upstream.

6.) ➞ The resulting debris can increase the erosion of the plunge pool
➜ by increasing erosive power

Question 5

• What is the formation of a ‘v-shaped valley’?

Answer 5

BEGINNING:
1.) ➞ The river channel erodes downwards
➜ due to VERTICAL EROSION

MIDDLE (PROCESSES):
2.) ➞ Erosion occurs through:
1. ‘hydraulic action’
➜ (the force of water compresses air trapped in the bank, creating an explosive blast, causing materials to be dislodged 💥)
2. ‘abrasion’
➜ (the force of water throws bedload against the banks, wearing them down 🪨)
3. ‘solution’
➜ (acidity in the water dissolves the rocks 🧪)

ENDING (FINAL PROCESSES):
3.) ➞ The river only erodes a small section of the valley

4.) ➞ Material is moved down the valley sides by MASS MOVEMENT
➜ for example, FROST HEAVE (expansion and contraction of soil, due to changing temperatures, dislodges soil) and gravity.

5.) ➞ This material adds to the erosive power of the river
➜ increasing erosion of the river bed.

Question 6

• What is the formation of a ‘meander’?

Answer 6

BEGINNING:
1.) In a straight river channel, water turns around obstructions (such as boulders)
↳ resulting in areas of slower (pools) and faster (riffles) water (as it becomes more sinuous)

2). Riffles & pools 🌊
↳ lead to changes in speed & depths in the river channel
➜ as pools are deeper whereas riffles are shallower
(with greater turbulence)

MIDDLE (PROCESSES):
3.) Erosion occurs through:
1. ‘hydraulic action’
➜ (the force of water compresses air trapped in the bank, creating an explosive blast, causing materials to be dislodged 💥)
2. ‘abrasion’
➜ (the force of water throws bedload against the banks, wearing them down)
3. ‘solution’
➜ (acidity in the water dissolves the rocks 🧪)

ENDING (FINAL PROCESSES):
4.) Rivers flow fastest on the outside bend
↳ as there is increasing erosive power ⚡
(causing undercutting & the formation of river cliffs)

5.) Rivers flow slowest on the inside bend
↳ leading to deposition ⏳

6.) HELICOIDAL FLOW 🪛
↳ transfers sediment from the river cliffs to river beaches in a corkscrew movement

7.) Meanders migrate downwards
↳ as erosion continues.

Question 7

• What is the formation of an ‘ox-bow lake’?

Answer 7

BEGINNING:
1.) Riffles & pools
↳ lead to changes in speed and depth in the river channel
➜ as pools are deeper, whereas, riffles are shallower (with greater turbulence)

MIDDLE (PROCESSES):
2.) Erosion occurs through:
1. ‘hydraulic action’
➜ (the force of water compresses air trapped in the bank, creating an explosive blast, causing materials to be dislodged 💥)
2. ‘abrasion’
➜ (the force of water throws bedload against the banks, wearing them down 🪨)
3. ‘solution’
➜ (acidity in the water dissolves the rocks 🧪)

ENDING (FINAL PROCESSES):
3.) Rivers flow fastest on the outside bend
↳ increasing erosive power ⚡
(causing undercutting and the formation of river cliffs.)

4.) Rivers flow slowest on the inside bend
↳ leading to deposition ⏳

5.) HELICOIDAL FLOW 🪛
➞ transfers sediment
↳ from the river cliffs to river beaches
➜ in a corkscrew movement.

6.) River cliffs retreat
↳ causing meanders to become more pronounced over time and the neck of the meander to become narrower.

7.) During a flood there is more energy
↳ and the water may cut through the neck 🌊

8.) Deposition seals off the old meander
↳ and over time the abandoned channel may dry up ⏳