Upper Course Processes and Features Flashcards
What is a waterfall?
A steep fall of water along the course of a river. It is a break in the profile of a river and is usually the result of the river flowing over an area where harder rock (caprock) overlays softer rock.
How is a waterfall formed?
1) Differential erosion (occurring where there is a junction between a hard rock capping upstream and soft rock downstream) causes the river to erode the soft rock and the water to fall vertically from the hard rock to soft rock below.
2) a) splash back causes hydraulic action to weaken the rocks behind the fall of the water.
b) pieces of soft rock break off and an indentation is formed at the base.
c) continued undercutting means that hard rock capping loses support and overhangs the drop.
3) a) the unsupported cap rock breaks off
b) the fallen rock breaks up and is caught in the turbulent flow of water. Some rocks become trapped and drill into the bed, which creates a plunge pool.
c) undercutting continues creating a new overhang. As this process of headward erosion repeats, the waterfall retreats upstream leaving a gorge downstream.
What is the first stage of the formation of interlocking spurs?
The rivers water volume and discharge are low. The river uses most of its energy overcoming with the channel. What energy it has left over is used by hydraulic action to deepen the channel (vertical erosion).
What is the second stage of the formation of interlocking spurs?
In upland areas, the geology is composed of hard rock such as granite or slate. However, freeze thaw weathering gradually broadens it out. This gives the valley a steep, V-shaped cross profile. Repeated weathering weakens the rock so fragments break lose and tumble down the hillside as scree, which the river then removes.
What is the third and final stage of the formation of interlocking spurs?
The winding path taken by the river is due to obstacles of harder rock in its path. The river takes the easiest route over land. This results in projections of high land entering the valley from alternate sides. These projections are the interlocking spurs.
How are rapids formed?
Alternating vertical layers of hard and soft rock cause differential erosion, where the soft rock is eroded first. This causes up and down layers of rock. The water is then pushed up and down over the rock, causing it to become turbulent and form rapids.
