GCSE EDEXCEL B GEOGRAPHY - topic 4

The UK's evolving physical landscape (river processes and pressures)

abrasion

A process of erosion where rocks and sediment are picked up by the river and grind against each other, resulting in the wearing away of surfaces. most erosion happens by abrasion

attrition

A process of erosion where rocks and pebbles collide and break into smaller pieces as they are transported by the river, wearing each other away.

hydraulic action

A process of erosion caused by the force of moving water, where the pressure of water enters cracks in rocks and river banks, causing them to break apart and wear away over time.

solution

a process of erosion when alkaline rocks such as limestone are dissolved by acidic water, leading to the weakening and removal of material.

traction

a method of sediment transport where large particles such as boulders are rolled or dragged along the riverbed by the force of the water, contributing to the river's erosion and sedimentary processes.

saltation

a method of sediment transport where smaller particles such as sand and pebbles are lifted and then dropped in a series of leaps or hops along the riverbed, resulting in a skipping motion

suspension

a method of sediment transport where very fine particles, such as silt and clay, are carried within the water column, making them invisible, while still contributing to the river's load.

solution

a method of sediment transport where minerals are dissolved in water and carried along in solution, contributing to the river's overall load.

how are meanders formed?

Meanders start as slight bends. Water flows faster on the outer curve of the bend and slower on the inner curve of the bend. Therefore, the outer curve erodes more rapidly while sediment is deposited on the inner curve, gradually increasing the bend and forming a meander.

how is an ox-bow lake formed?

An ox-bow lake is formed when a meander becomes extremely curved due to erosion, and eventually, the river cuts through the narrow neck of land, creating a new, straighter river channel. The abandoned meander loop is then left behind and deposition at the neck seals off the bend and as the old meander bend begins to dry up, it forms an ox-bow lake.

How are interlocking spurs formed?

In the upper course of a valley, the river does not have a huge amount of energy to erode as it does noy have a high discharge and has to transport large pieces of sediment. So, when the river meets areas of harder rock that are difficult to erode, it winds around them. A series of hills form on either side called spurs, creating a series of interlocking spurs as it cuts into the softer surrounding land.

how are waterfalls formed

waterfalls such as the severn-breaks-its-neck along the river severn are usually formed in the upper course of a river when areas of hard rock overlay an area of soft rock which tends to erode faster. As the water starts to erode the soft rock it creates a steep gradient and the erosion of the soft rock underneath undercuts the hard rock, resulting in an overhang (ledge). Hydraulic action and abrasion work together to create a plunge pool at the foot of the waterfall.

how is a gorge formed?

Gorges are formed as a result of the retreat of a waterfall over time towards the source, creating a deep, narrow valley with steep sides. This process involves the erosion of softer rock by the waterfall, leading to undercutting of harder rock and the collapse of overhangs, causing the waterfall to gradually retreat upstream. 

How does erosion help form landscapes?

Erosion shapes landscapes by removing soil and rock, transporting materials, and carving features such as valleys, cliffs, and gorges. Through processes like weathering and sediment transport, erosion contributes to the creation of various landforms, including interlocking spurs.

how is a floodplain formed?

Floodplains are formed through a combination of erosion and deposition processes in the lower course of a river. As a river meanders, it erodes the outer banks, widening the river channel and creating a flat, low-lying area. During floods, the river loses energy and deposits sediment (alluvium) on the floodplain, gradually raising its level. This process repeats over time, leading to the development of a wide, fertile floodplain.

how is a delta formed?

deltas are low-lying areas of land where a river meets a sea or a lake, formed by deposition occurring due to the result of a sudden reduction in the river’s velocity. If the river deposits sediment faster than the coastal processes can erode it, the material builds up and the main channel gets blocked. This forces the water to find alternative routes to the sea by making distributaries. The only delta in the UK is the wash in norfolk and linconshire.

how is a levee formed?

Levees are naturally formed, raised riverbanks in the lower course of a river, typically found on either side of the channel. They are formed through the repeated deposition of sediment during floods. When a river overflows its banks, the water slows down and loses its ability to carry sediment, causing larger particles to drop off close to the riverbank. Over time, these deposits accumulate, building up the riverbanks and creating levees.

named river?

river severn

How do river landscapes change between the upper, middle and lower course of a river?

UPPER:

1. vertical erosion and soil creep, mass movement and some transportation

2. v-shaped valleys and spurs, waterfalls and gorges

3. narrow river channel and rough beds, hard and impermeable shales and grits as well as angular stones

MIDDLE:

1. lateral erosion and deposition, some transportation

2. meanders and wider + flatter valley floors, oxbow lakes and floodplains

3. softer and more permeable rock like sandstone

LOWER:

1. transportation and deposition, lots of lateral erosion

2. bigger floodplains and deltas, wider river channels, and significant sediment deposition.

3. soft mudstone covered with alluvium, sand and gravel

river channel characteristics - UPPER

• river channel is narrow and shallow

• the discharge is low

• the velocity is low

• sediment size is large and angular

• gradient at its steepest

• lots of rainfall

river channel characteristics - MIDDLE

• river channel widens and deepens

• asymmetrical shapes on meanders

• discharge increases

• velocity increases

• sediment is a lot smaller and more rounded / smoother

• gradient reduces

river channel characteristics - LOWER

• river channel is at its widest and deepest

• discharge is at its greatest amount

• velocity is at its fastest

• sediment is very small and smooth

• gradient is at its lowest

how and why does gradient change down ur named river

In the upper course, the river's gradient is steep, leading to rapid erosion and a V-shaped valley. As the river flows downstream, the gradient decreases, and the valley broadens. 

how and why does discharge and velocity change down ur named river

Discharge (volume of water) and velocity (speed of flow) increase downstream as tributaries join the main river. This increased water volume and speed, combined with the decrease in gradient, leads to a wider, deeper, and smoother channel. 

how and why does the channel shape change down ur named river

The river channel changes from narrow and shallow in the upper course to wider and deeper in the lower course. This is primarily due to lateral erosion in the middle and lower courses, where the river erodes its banks. 

how and why does sediment size and shape change down a river

In the upper course, the river carries larger, angular sediments due to its high erosive power. As the river flows downstream and the velocity decreases, sediments become smaller and more rounded through attrition (clash between sediments)

how and why does the valley profile down ur named river change

In the upper course, the valley is steep-sided and narrow, often resembling a V-shape due to vertical erosion. As the river moves downstream, the valley floor widens, and the valley sides become gentler due to lateral erosion. 

Influence of sedimentary rock on river landscapes and sediment load

Sedimentary rocks are formed in layers from small particles. They tend to be softer, less resistant rocks that are permeable (allow water to pass into and through them). Examples include mudstone and sandstone. River water can erode vertically and laterally into this rock type with ease making the channel shape deeper and wider. This also widens the river valley (valley profile) leading to the formation of floodplains. As the rock is soft the river will erode the banks and beds easily which increases the sediment load of the river.

influence of igneous rock on river landscapes and sediment load

Igneous rocks form from molten magma. They are harder, more resistant rocks. They are also impermeable (do not allow water to pass through them). Examples include granite and basalt. A river flowing over this geology will have high runoff due to the impermeability but also there will be limited erosion as the rock is resistant. Therefore there may only be some vertical erosion, leading to the formation of a V-shape valley with steep vertical sides (valley profile). Due to the rock being resistant, less material will be eroded and weathered so the sediment load will be lower than in areas of softer, sedimentary rock.

influence of metamorphic rock on river landscapes and sediment load

Metamorphic rocks such as marble, slate and quartzite are rocks that form from existing rocks that are transformed by great heat or pressure. They are resistant and durable, similar to igneous rocks and will therefore have the same impact on the river landscape and sediment load as igneous rocks do.

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