Geography- Unit 1.2.1/ How do rivers change overtime?

Question 1

Abrasion

Answer 1

The movement of rocks grinding against other rocks thus eroding them through a sandpaper like affect

Question 2

Attrition

Answer 2

Rocks hitting each other and breaking apart into smaller rocks.

Question 3

Hydraulic action

Answer 3

Rapid water movements with high energy hitting rocks/ other material and thus eroding it and pushing cracks in rocks

Question 4

Solution

Answer 4

Certain rocks are dissolved in water e.g limestone.

Question 5

Traction

Answer 5

Movement of large boulders rolling across the floor from water pushes.

Question 6

Suspension

Answer 6

Smaller particles are held up in the water and moved down stream/ current/ tide.

Question 7

Saltation

Answer 7

Smaller rocks hit the sides of the river, causing others to bounce of, thus creating a cycle.

Question 8

Deposition

Answer 8

when a river loses energy and drops the material it carries.

Question 9

fluvial erosion

Answer 9

Erosion that occurs in a river

Question 10

Why does deposition occur?

Answer 10

-Decrease in velocity gradient
- Too much load (caused by landslides)
-Less water/ shallow water
-Too much water e.g floodplain.

Question 11

What is the Hjulstrom curve?

Answer 11

-With higher velocity, more particles are eroded
- In water with less velocity and smaller particle sizes are transported
- Larger particles even with slightly high velocity are deposited
- Larger particles ( silt or other materials) are deposited.

Question 12

How is a waterfall formed?

Answer 12

1) A layer of softer rock such clay is covered partly by a harder more resistant rock such as granite.
2) Hydraulic action erodes the uncovered weaker rock and creates a plunge pool that begins to undertrack towards the weaker rock underneath the harder rock.
3) The overhanging harder rock collapses
4) The collapsed rock causes more erosion through ablation.
5) therefore a large drop structure is formed called a waterfall

Question 13

Waterfall formation key words?

Answer 13

• Resistant rock
• Less resistant rock
• Plunge Pool
• Undercutting
• Overhang
• Hydraulic action
• Abrasion

Question 14

What is a gorge?

Answer 14

The retreating path of a waterfall and is a narrow cleft with steep rocky walls, normally with a stream flowing through it.

Question 15

How is a gorge formed by erosion?

Answer 15

Same as a waterfall, however this process of weaker rock eroding and leaving the more resistant rock to overhang and eventually collapse is repeated. Additionally, vertical erosion takes part in this process.

Question 16

Name the five ways in which a gorge can be formed.

Answer 16

-Erosion
-Geological uplift
-Erosion and geological uplift
-Melting of glaciers
-backwards pathway of waterfalls

Question 17

What is Lateral erosion?

Answer 17

It is the eroding of the banks (sides) of a river, broadening it.

Question 18

What is vertical erosion?

Answer 18

the eroding of the bed of a river, deepening it.

Question 19

Example of a uk Gorge?

Answer 19

Cheddar Gorge.

Question 20

How was cheddar gorge in england formed and what shape is it?

Answer 20

By periglacial flooding, and the shape near scarps loop where it exits into a valley, the cross section is far more wide than earlier on in the coarse.

Question 21

What are interlocking spurs?

Answer 21

Interlocking spurs are the winding shape of a river around higher land made from more resistant rock.

Question 22

How are interlocking spurs formed?

Answer 22

The river winds around the harder rock and instead erodes the softer rock by ts side, creating s shaped structure.

Question 23

What is a v-shaped valley?

Answer 23

An elongated depression between uplands hills or mountains, formed by erosion and weathering or the melting of glaciers.

Question 24

How is a v-shaped valley formed?

Answer 24

Vertical erosion causes the river bed descend and the depression between the upland to elongate. Weathering causes the soil/rock on the step like sides of the valley to loosen and be washed into the river/ slope transport.

Question 25

What is weathering?

Answer 25

Weathering is the deterioration of rocks, soils and minerals through contact with water, atmospheric gases, sunlight and biological organisms.

Question 26

How are Meanders and and ox-bow lake formed?

Answer 26

1)The water’s discharge will bend around the harder rock, hitting an area of softer rock and therefore erode it. This causes a bend.
2) By hydraulic action, the rapid water hits and erodes the inner curve of the bend, and sedimentation will occur on the outer curve, causing the curve to almost create a full circle.
3)Due to throughway, once the neck is cut and the circle comes together, the water will flow in a straight line and not around the meander.
4) sedimentation cuts of the meander, and an oxbow lake is formed.

Question 27

Meander key words

Answer 27

-Throughway
-sedimentation/deposition
-erosion

Question 28

What is a Slip off slope and how does it form a meander?

Answer 28

The water moves around the raised area of sand and shingles, the slip off slope, and undercuts the bank causing the bend.

Question 29

What is a floodplain and where are the found?

Answer 29

Expansive flat land (with silt build up) either side of a river that floods when the river has too much discharge.
Lower coarse.

Question 30

How do levees form in a floodplain?

Answer 30

When there is too much discharge, the water will overflow onto the floodplain. As the water travels over the rover banks, it loses energy and immediately deposits its larger sediment. This builds up to form wall like structures called levees which in turn, raises the river channel and decreases its chance to flood again.

Question 31

What occurs in the upper course of a river?

Answer 31

Lots of vertical erosion and therefore v-shaped valleys, waterfalls, and interlocking spurs.

Question 32

What occurs in the middle course of a river?

Answer 32

More lateral erosion, causing more formations such as meanders.

Question 33

What occurs in the lower course of a river?

Answer 33

Same as the middle coarse, however with more room for discharge, there is less pressure and energy causing deposition and formation of islands.

Question 34

Why do rivers flood? x3

Answer 34

• Saturated or too dry soil.
• Paving over soil, creating an impermeable surface
  -Deforestation (plants absorb water)

Question 35

What is a hydrograph?

Answer 35

The rate of flow/ discharge versus the time past, showing how a river is affected by a storm/ lots of rainfall.

Question 36

Hydrograph analysis

Answer 36

1. Lag time- the time between the peak rainfall and peak discharge
2. Peak discharge
3. Peak rainfall- on the bar chart
4. Raising limb
5. Falling limb
6. Baseflow/ antecedent- normal flow of the river.
7. Bankfull discharge- horizontal line showing when a flood might occur

Question 37

What causes the lag time?

Answer 37

The water from the peak rainfall will be absorbed in the soil or by plants, causing it to become throughflow (flowing underground), preventing it from reaching the river quickly.

Question 38

What affects the length of the lag time?

Answer 38

If the soil is saturated, or too dry or has an impermeable surface such as pavement covering it (urban areas) water will not be absorbed and therefore will become runoff and join the river quickly, causing more discharge.

Question 39

What are the four stages in a hydrograph?

Answer 39

1) Channel precipitation- during the lag time, water falling directly on a rivers surface within a channel.
2) Overflow- during the rising limb, water begins to raise over the banks of a river.
3) throughflow- during the falling limb, runoff has ceased and the water flows much slower into the river through the soil
4) Groundwater flow- During the baseflow and end of the falling limb, it is the very slow movement of water through porous rocks into the river.