4.6 Landscapes And Processes Flashcards
What is meant by the long profile of a river?
The long profile of a river is the horizontal view of the river. It shows us the gradient of the whole river (upper, middle and lower course).
Define weathering
Weathering is different processes that are natural erosive forces. The main types of weathering are biological, chemical and physical.
Compare freeze thaw and biological weathering.
Freeze thaw weathering is when water freezes inside a crack and expands but then contracts when it melts. This is a physical process as it physically forces the rock apart.
Biological weathering is when vegetation grows roots into cracks and expand, forcing the rocks apart. Animals, such as rabbits, also dig burrows that cause the rock to be unstable and is much more likely to break up.
Compare traction and suspension transport?
Traction is when large pieces of sediment are slowly rolled along the river bed. Traction mainly occurs in the upper course.
Suspension is when very fine pieces of sediment is held up or suspended inside the water. This mainly occurs in the lower course as the sediment has been eroded down by abrasion and attrition.
Explain the stages and processes responsible for a waterfall formation?
A layer of more resistant rock lies over a layer of less resistant rock.
The less resistant rock erodes more easily by abrasion (sediment knocking against the rock) and hydraulic action (water and air is compressed into small cracks and enlarge the crack, slowly breaking off chunks).
The river’s bed load swirls around at the foot of the waterfall and gradually erodes the river bed to form a plunge pool.
The plunge pool erodes backwards and leaves the overhanging rock unsupported. The more resistant rock collapses and the waterfall retreats.
The more resistant rock that collapsed increases the erosion in the plunge pool.
This is erosion and retreating is repeated until a steep-sided valley, called a gorge, is formed.
Explain the stages and processes that are responsible for a v-shaped valley formation?
The river is very narrow, in the upper course, and there is high Gravitational Potential Energy so the erosion is vertical rather than horizontal.
Weathering occurs on either side of the river. Freeze thaw weathering occurs when water is trapped in cracks. At night, the water freezes and expands. During the day, the water melts and shrinks. This is repeated until the rock is broken apart. Chemical weathering is when rocks, such as limestone, is dissolved due to the rain water being slightly acidic. Biological weathering occurs when vegetation grows its roots into cracks and expands, breaking apart the rocks.
Scree slopes occur often due to the weathering so rockfalls are common. The broken sediment is transported downstream; the sediment increases vertical erosion, especially abrasion.
The slope is completely eroded so a v-shaped valley has formed; the sediment is transported down the river.
Interlocking spurs is when there are bands of more resistant rock. The river weaves in between the spurs and the spurs are interlocking so it forms interlocking spurs.
Explain the formation of a meander and ox-bow lake?
When rivers enter their middle and lower stages they begin to erode sideways (laterally) and form large bends called meanders.
The river erodes on the outside of the bend where the current flows strongest and fastest. This washes away the river bank creating a river cliff. On the inside of the bend where the water flows weakest, it deposits its load, forming a slip off slope. Over time the erosion and deposition continue, changing the course of the river and moving it slowly down the valley.
When the river meander reaches the sides of the valley, it erodes them, widening the valley floor and flood plain. Over long periods of time some meanders can loop back on themselves until only a narrow neck of the land is left.
An ox-bow lake is formed when erosion, through hydraulic action and abrasion, causes the outsides bends to get closer. Until only a small bit of land is left between the bends. This small bit of land is called the neck. The river breaks through, usually during a flood. The river now flows through the shortest course. Deposition occurs and eventually cuts off the meander. This forms an ox-bow lake.
Explain how flood plains form?
The main process in the lower course is lateral or horizontal erosion and deposition. The river is carrying a lot of sediment as it has gathered it from many different tributaries. At a meander bend the river erodes on the outer bend and deposits on the inner bend. The river slowly migrates; it moves the river downstream and outwards. After time, the river erodes into the hills and creates a very wide and flat area next to the river, called a floodplain. When the river floods, the water flows all over this wide, flat area. The river flows slower as friction is increased. The land becomes fertile as the sediment is deposited.
Explain how levees are formed?
Levees are formed by deposition during a flood. The river’s load is composed of different sized sediment. When the river floods, the flow of water is slowed and the kinetic energy is lost so the river deposits the heaviest sediment first and then the lighter sediment. The larger sediment, usually shingle, is deposited and forms levees, which is a natural embankment. The sands and silts are deposited next and build the levees and floodplain up.
Explain how deltas are formed?
When a river reaches another body of water such as a sea or ocean, it loses velocity and deposits sediment. If the river deposits sediment faster than coastal processes erodes it, sediment builds up in layers in a fan-shaped delta. The river splits into many smaller channels called distributaries and creates large areas of wetlands.
Label the key features of a flood hydrograph?
Peak rainfall:
When the heaviest rainfall occurred.
Peak discharge:
The time with the highest river discharge.
Lag time:
The time taken between peak rainfall and peak discharge. A smaller lag time is worse while a greater lag time means that it would be less destructive and less powerful.
Rising limb:
The river level is rising. Greater gradient the faster the increase of the river level.
Falling limb:
The river level is falling.
Flashy hydrograph:
A hydrograph that responds quickly to rain, with a high peak and short lag time.
Compare a flashy and subdued hydrographs.
A flashy hydrograph has a high peak discharge but with a very short lag time. This means that from the point of which the highest rainfall occurred to the point of the highest discharge of the river occurred.
A subdued hydrograph has a big lag time and a low peak discharge. The rising limb has a very low gradient.
Explain how physical factors can affect a hydrograph?
Impermeable rocks:
Igneous rocks and hard sedimentary rocks are impermeable so the water cannot infiltrate and surface run-off is increased.
Thin soil:
There is a smaller volume of soil so it cannot hold as much water so therefore it saturates easily and increases surface run-off.
Steep relief:
Steep relief means that the water flows down towards the river at a faster rate as the gradient is steeper and surface run-off is increased.
Antecedent conditions:
Wet antecedent conditions means that there is a lot of precipitation so therefore soils will saturate quickly and the river will increase in discharge and therefore increase the peak discharge.
