River Landscapes Flashcards
When does mechanical weathering happen? (River)
This happens when rainwater enters cracks or gaps in the rock and then freezes if temperatures drop below zero. The water expands as it turns into ice and then exerts pressure on the rock causing it to break into smaller pieces
What is chemical (acid rain) weathering? (River)
All rainwater is slightly acidic. If the air is polluted by factories and vehicles, it can become more acidic. When rain falls on rocks, the acid in it can react with weak minerals, causing them to dissolve and the rock to decay.
What is biological weathering? (River)
The roots of plants, especially trees can grow into cracks in a rock and split them apart
What is mass movement?
Mass movement is the movement of rocks and soil downslope due to gravity, helped by weaker rocks, steep slopes and heavy rainfall. Mass movements can be very slow - only a few mm a year - or sudden and rapid. Types of mass movement that affect river valleys include soil creep, sliding and flows
What is sliding? (River)
Where material moves rapidly downslope in one go, for example in a landslide. In a slump, the material often rotates as it moves
What is soil creep?
It is a form of mass movement where individual particles of soil move slowly down a slope
What is Hydraulic action? (River)
This results from the sheer force of the water hitting the river bed and banks and wearing them away. This action is particularly important during high-velocity flow.
What is attrition? (River)
It is a form of erosion, when sediment particles carried in the river collide with each other, causing the edges to be knocked off. The continued collision of particles in the river causes them to become rounder and smaller downstream
What is solution? (River)
It is a form of erosion, which is when the river water is lightly acidic, so it can dissolve some rocks and minerals in contact with the he river. Limestone and chalk are most affected
What is abrasion? (River)
It is a form of erosion which is caused by material carried in the river rubbing against the bed and banks of the channel, so wearing the away. Overall abrasion causes the most erosion
Describe the transportation of a load in a river
A river picks up and carries material as it flows downstream. The four types of transportation are traction, saltation, suspension and solution
What is deposition? (River)
When a river no longer has enough energy to carry its load, deposition occurs. As the rivers discharge and velocity reduce, the heaviest material is deposited first, for example after flooding
What is traction?
It is a form of transportation, for when large boulders are rolled along the river bed
What is suspension?
It is a form of transportation for when finer sand particles are carried along in the flow, giving a brown appearance
What is saltation?
It is a form of transportation for when smaller pebbles are bounced along the river bed, picked up then dropped as the river flow changes
What is solution? (In transportation)
For when minerals, such as chalk are dissolved in the water and carried along in the flow, although they cannot be seen
Where do rivers and the valleys they flow in change in different ways?
Between their source (where they start) and their mouth (where they join the sea)
Describe a river profile
A rivers profile shows the height and distance downstream from the rivers source to its mouth. It is a curved shaped, steeper near the source and flatter near the mouth
describe the gradient in the upper, middle and lower course
Upper - steep
Middle- less steep
Lower - shallow gradient
Describe the discharge in the up, mid, low course
Up - smaller
Mid - large
Low - very large
Describe the depth in the up, mid, low course
Shallow, deeper, deep
Describe the channel shape in the up, mid, low course
Up - narrow, steep sides
Mid - flat, steep sides
Flat floor, gently sloping sides
Describe the velocity in the up, mid, low course
Up - quite fast
Mid - fast
Low - very fast
Describe the valley profile in the up, mid, low course
Up - steep sides
Mid - flat with steep sides
Low- flat with gently sloping sides
Describe the features in the up, mid, low course
Up - waterfalls, interlocking Spurs
Mid - meanders, floodplain
Low- meanders, floodplain, levées, ox-bow lakes
Describe the sediment shape and size in the up, mid, and low course
Up - angular boulders
Mid- more rounded rocks
Low - smooth, rounded pebbles
How does the uk’s water and climate have an effect on river processes ?
Causes changes to landforms and landscapes
With the impact of climate What is the erosion rate?
Erosion rate will be higher with grater discharge, so rivers in wet climates will erode more material than those in dry climates, widening and deepening river valleys and increasing the amount of eroded sediment
With the impact of climate, what is the transport rate?
The transport rates will be grater where the energy of the water is greater, so rivers in wet climates will transport more material than those in dry climates
With the impact of climate what is the amount of discharge?
The amount of discharge is affected by climate. Wetter climates mean greater discharge. Hotter temperatures mean greater evaporation so less discharge. The greeter the discharge, the height the velocity of the river
With the impact of climate what is the weathering.,
The weathering of rocks will be greater in some climates: for example, freeze-thaw weathering increase where temperatures range from just below freezing
How can increasing frequency of storms increase the risk of flood?
More periods of heavy, intense rainfall meaning more water flowing into rivers, which then overflow
How can increasing periods of hot dray weather increase the risk of flood?
It bakes the upper soli is when it does rain the water runs off the surface, it can’t soak in, reaching rivers and rapidly increasing discharge
How can soil becoming impermeable during cold conditions increase the risk of flood?
Snowmelt cannot infiltrate and flows rapidly into rivers increasing flood risk
how are interlocking Spurs, waterfalls, gorges and river cliffs formed?
By erosion processes and the influence of geology in the upper course of the river
What are interlocking Spurs?
Near the rivers source, rivers are small and do not have a lot of power. They tend to flow around valley slide slopes, called Spurs, rather than being able to erode them. The Spurs are left interlocking, with those from one side of the valley overlapping with the Spurs on the other side
How are waterfalls formed?
A waterfall is formed along a river when a band of hard, more resistant rock lies over a band of soft, less resistant rock. The river erodes the less resistant rock at a faster rate, gradually undercutting the more resistant rock. The continued erosion of the soft rock by abrasion and hydraulic action causes an overhang of the hard rock. Eventually the hard rock cannot support its own weight and collapses under the force of gravity. The force of the falling water and abrasion by large angular boulders leads to erosion of the river bed and formation of a plunge pool
How are gorges formed?
After a waterfall is formed, as the soft rock continues to be eroded and the hard rock collapses, a steep-sided gorge is formed as the waterfall retreats upstream. Gorges form in hard rocks, where vertical erosion by rivers is dominant.
What is the weathering process?
Weathering is the wearing away in situ of the river valley side. There are three weathering processes common to the river valleys
How is a plunge pool formed?
Hydraulic action and abrasion
What is a floodplain?
A flood plain in the flag area of land either side of a river in its lower course. It is formed by erosion and deposition. Lateral erosion on the outside bends of meanders means they migrate across the valley floor and can erode the valley sides, so the valley floor becomes wide and flag. During floods, the flood waters spread out across the valley floor. As they slow down, with less energy for transport, the river deposits fine sediments called alluvium.
How is a flood plain shaped?
In the lower course, the river is nearing the sea and carries a huge amount of sediment (alluvium)
When the river floods,excess water spills over the. Surrounding areas urging flooding, the velocity of the river is reduced, it loses energy, and deposits sediment , forming the floodplain
The floodplain is shaped by the lateral erosion of meanders as they gradually migrate downstream and by deposition of material of the inner bends
What are levees?
Levees are natural embankments of sediment formed along the banks of rivers that carry a large load and occasionally flood. In times of flood, water and sediment come out of the channel as the river overflows its banks. As it overflows, the river immediately loses velocity and energy and deposits the larger and heavier sediment first, on its banks, repeated flooding causes these banks to get higher, forming levees.
Go and look at the diagram
On page 19
How are the landforms meanders and ox-bow lakes created?
But the interaction of deposition and erosion process in the middle and lower courses of a river
What are meanders?
Meanders are bends found in a rivers course, commonly found on a rivers flood plain. The flow of the water swings from side to side, directing the line of maximum velocity and the force of the water towards the outside of the bend. This results in lateral erosion by undercutting and an outer, steep bank is formed. This is called a river cliff. On the inside of the bend the velocity and force of the water is less, leading to deposition and the formation of gently sloping bank known as a slip-off slope. The material deposited is called a point bar and is characteristically curved in shape. Due to erosion and deposition, the cross section of a meander is asymmetrical-steep on the outside of the bend, gentle on the side.
What is a river cliff?
In the outer bend of a meander, where the current is faster, there is greater erosion. This wears away the bank creating a river cliff
What is a point bar?
On the inner bend of a meanders, where the current is slower, there is greater deposition, creating a point bar
