Rivers - Fluvial Processes

Question 1

Weathering

Answer 1

• The breakdown of rock, in situ, normally due to weather, especially rainfall and temperatures
• Usually on the banks + valleys

Question 2

Erosion

Answer 2

• The breakdown and removal of material by the river
• Usually happening in the channel
• includes the movement of broken down material

Question 3

Physical weathering

Answer 3

The breakdown of rocks into smaller and smaller pieces. Done by changes in temp (alternate expansion and contraction of rocks) and by rainfall (freeze-thaw weathering)

Question 4

Chemical weathering

Answer 4

Causes rocks to dissolve, decay and disintegrate, then forming new substances by chemical reactions. For example acid rain seeping into porous rocks. (E.g. chalk, limestone or sandstone)

Question 5

Biological weathering

Answer 5

• Disintegration of rocks due to the actions of plants/ animals

Question 6

Mass movement

Answer 6

Rocks are broken down by weathering and this weathered material begins to move downslope under the influence of gravity

Question 7

Slumping

Answer 7

When the bottom of a valley side slope is cut away by the river flowing at its base, the weathered material above it becomes unstable and slumps down the slope, under gravity. This can be made more likely if the soil at the top is saturated or if people have built or walked upon it

Question 8

Soil creep

Answer 8

Weathered material moves slowly downslope, under the influence of gravity, collecting at the base at the slope, where it is eroded by the river

Question 9

Erosion

Answer 9

1. Abrasion - when material carried by the river rubs against the riverbed and sides, wearing it away
2. Attrition - where bedload in the river hits into one another and breaks apart.
3. Solution - when minerals in the rock are dissolved by the water in the river
4. Hydraulic action - The force of the river compresses air trapped in cracks in the banks. The increased pressure weakens and gradually wears away the banks

Question 10

Transportation

Answer 10

1. Traction - when large boulders roll along the river bed
2. Saltation - when small boulders bounce along the river bed
3. Suspension - when small rocks are carried along in the river flow
4. Solution - when dissolved particles are carried along in the river flow

Question 11

Deposition

Answer 11

Definition: the laying down of material transported by the river, occurring when there is a decrease in energy, speed and discharge

Large particles - these are deposited first as the river loses energy and these are the heaviest

Small particles - these can be transported for miles and are usually deposited nearer the mouth of the river

E.g. inside bend of a meander, in areas of shallow water and at the mouth of rivers

Question 12

Long profile

Answer 12

Shows how a river runs from its source to the point where it enters the sea, a lake or joins another and larger river

Question 13

Three courses in a river

Answer 13

Upper, middle and lower

Question 14

Upper course landforms

Answer 14

• steep V-shaped valleys
• interlocking spurs
• waterfall
• gorges
• large rocks and boulders

Question 15

Lower course landforms

Answer 15

• meanders
• oxbow lakes
• estuaries
• flood plains
• levees
• fine sand particles

Question 16

Middle course landforms

Answer 16

• Meanders
• oxbow lakes
• floodplains
• smaller pebbles and rocks

Question 17

Upper course river and valley characteristics

Answer 17

• The river flows downhill due to gravity. This creates friction and results in lots of vertical erosion
• The river channel is narrow and shallow
• The valley is V-shaped with steep sides

Question 18

Middle course river and valley characteristics

Answer 18

• Lateral erosion increases as the river becomes less steep
• The river channel is wide and steep
• The valley is V-shaped with shallow sides

Question 19

Lower course river and valley characteristics

Answer 19

• A lot of lateral erosion occurs
• The river channel is very wide and deep
• The valley sides are wide and almost flat
• Deposition is the most evident

Question 20

Interlocking Spurs

Answer 20

1. In the upper course of a river, water and the material it carries cut into the river bed, creating a steep-sided V-shaped valley
2. The river is not powerful enough to erode laterally through areas of hard rock, so it winds and bends around these rocks
3. The winding path of the river creates a winding valley of interlocking Spurs

Question 21

Waterfalls and gorges

Answer 21

1. Waterfalls form where there are rocks of varying hardness and density. Softer, less dense Rock is eroded away faster than the overlying hard rock.
2. Soft rock is eroded easily through hydraulic action and abrasion, enabling the river to cut down into the channel.
3. Over thousands of years, the river continues to erode the soft rock.
4. The overlying hard rock is undercut and left unsupported until it eventually collapses
5. The falling hard rock causes further erosion through abrasion, and the waterfall begins to retreat upstream
6. As erosion continues, the waterfall retreats upstream, leaving a steep-sided valley downstream. This is known as a gorge.

Question 22

Meanders

Answer 22

1. When a river gets nearer to the sea, larger bends develop as lateral erosion occurs.
2. Deposition takes place on the inside bend, where the river flows slowly. The shallow channel creates greater friction, which slows the river down.
3. Sand and shingle are deposited on the inside of the river bend, forming slip-off slopes.
4. Erosion and transportation take place on the outside bend, where the river flows fast. The deeper channel creates less friction, which enables the water to flow quickly.
5. Over time, erosion causes the riverbanks to be undercut and worn away, forming river cliffs

Question 23

Oxbow lakes

Answer 23

1. Erosion in the outside bend of a meander causes the neck of the meander to become narrower.
2. The neck of the meander continues to narrow until the river eventually breaks through to form a new river channel.
3. The river now flows along the shortest course, bypassing the loop.
4. As sediment is deposited on the riverbanks, the meander becomes sealed off.
5. An oxbow lake forms.

Question 24

Estuaries

Answer 24

1. Estuaries are found where the tidal mouth of a river meets the sea. Most were formed at the end of the Ice Age, when sea levels rose and caused widespread coastal flooding.
2. Estuaries are flooded daily by the tides as they rise and fall. At high tide, the incoming tide meets the out flowing river and reduces its velocity. This causes the river to deposit its sediment (sand and silt) over the floor of the river valley
3. Repeated flooding causes layers of sediment to build up over time, creating wide mudflats and salt marshes, which become exposed at low tide

Question 25

Floodplains

Answer 25

-> Floodplains are wide, flat areas of land found on either side of a river. They are extremely prone to flooding.

1. Rivers are contained within the banks during normal river flow levels
2. During flooding, river flows over the banks
3. Larger materials are deposited next to the channel as there is a loss of speed and energy
4. Smaller materials are carried up shore
5. Layers of materials called alluvium are formed on the banks; over time the height of the land increases and creates a flat wide area favourable for farming

Question 26

Levees

Answer 26

1. When a river floods over its banks, the water spreads out and slows down. As it does so, it loses energy and deposits the material it has been carrying
2. Heavier material is deposited first, closet to the channel. Finer, lighter material is carried further over the floodplain
3. Repeated flooding and deposition forms raised levees along the edge of the channel