4.6 Landscapes and Processes Flashcards
What is meant by the long profile of a river?
Shows you how the gradient changes over the different courses.
How does the river Eden’s landscape change along it’s long profile (upper/middle/lower)?
In the upper course of the river, the source is 600m above sea level and has hard, resistant rock. It has steep sides due to vertical erosion and has a steep gradient. The river channel is narrow and shallow which means the discharge of the river is low and so is its velocity. Large, angular rocks are carried in the upper course. In the middle course, it is made from sandstone which is a softer, less resistant rock and is easily eroded. This means the river becomes wider due to lateral erosion. The middle course valley sides have gentle slopes and the gradient is less steep. The river channel gets wider and deeper and the discharge increases as more tributaries join. There are many meanders here. In the lower course, the valley is very wide and flat, as it gets closer to Carlisle, it becomes only a few metres above sea level. The river has high velocity and little friction due to the smooth sides. Discharge is very large because 2 other rivers join in the lower course. The river channel is very deep and wide and material carried is very fine and is carried by solution and suspension.
What are the reasons for these changes ?
Weathering such as hydraulic action, abrasion, and solution all take place along the river course. There is vertical and lateral erosion.
Compare hydraulic action with abrasion
Hydraulic action is when water and air is forced into cracks and through repetitive motion is pulled away from the rest of the rock compared to abrasion which uses rock in the water and smashes them into other rock to speed up the process of erosion and breaking rock off.
Define weathering
Weathering breaks down rock through different processes.
Compare freeze thaw and biological weathering
Freeze thaw weathering is when water goes into cracks and freezes due to low temperatures. The water turns to ice and then expands. As the ice melts it decreases in volume and unsupported rock crumbles. Biological weathering however, is when plant roots grow into cracks in rock and slowly make the cracks bigger until it cracks off.
Compare traction with suspension
Traction is when large, angular rocks are rolled across the sea floor compared to suspension when smaller and finer bits of rock are suspended in the water as it moves.
Explain the stages responsible for waterfall formation
Waterfalls form where a river falls over an area of hard rock on top of an area of soft rock. The softer rock is eroded through hydraulic action and abrasion more than the hard rock causing an overhang to occur and a notch below. As more water falls, more soft rock is eroded and a plunge pool is created. This creates a steep drop. The hard rock becomes unsupported and collapses. The collapsed rock swirls around in the plunge pool deepening and widening it. This process is repeated many times and the waterfall retreats back leaving steep sides called a gorge.
Explain the stages responsible for v shaped valleys and interlocking
Vertical erosion occurs in the upper course, as there is not enough energy to laterally erode, this starts creating steep sides. After time, weathering occurs to the steep sides such as freeze thaw weathering due to high altitude. The weathered material then falls inward in the form of rock slides and scree slopes due to gravity and steepens the valley. What has been created is a v shaped valley and is a common upland occurrence. Interlocking spurs are formed when there are bands of more resistant rock and the river cannot erode these.
Explain the stages responsible for meanders
The current of a river in the middle course is faster on the outside and erodes it as there is more friction which causes bends to occur. The eroded material is deposited on the inside of the bend where the current is slower and shallower. These are called slip off slopes.
Explain the stages responsible for ox bow lakes
Erosion of meanders cause the outside bends to become closer together until there is only a small bit of land left called the neck. The river eventually breaks through and the river flows along the quickest and shortest path. Deposition eventually cuts of the meander forming an ox bow lake.
Explain the stages responsible for flood plains
A flood plain is the wide valley floor on each side of the river and the river floods onto these parts occasionally. The water slows down and material is deposited which builds up the flood plain making it higher. Meanders migrate across the floodplains making them wider and flatten out the valley floor as they move downstream.
Explain the stages responsible for levees
During a floods, eroded material is deposited over the whole flood plain. The heaviest material is deposited closest to the river channel. Overtime, this material builds up creating levees on the edges of the channel.
Explain the stages responsible for deltas
Rivers are forced to slow down when the exit near the mouth of the river channel. This causes them to deposit the material they’re carrying. If the sea doesn’t wash away the material it builds up and the channel gets blocked. Eventually, material builds up so much that low lying areas of land called deltas are formed.
Explain two ways climate, geology and slope processes change the river landscape
Rivers in wetter climates have higher discharge. Areas with softer rock will erode more, this adds more material to the rivers sediment load.
