Rivers - Processes and landforms Flashcards
What is a valley?
A low stretch of land between hills and mountains, often with a river flowing through it.
What is meant by a river’s course?
The course is the path a river takes as it flows downhill.
What is a drainage basin?
An area of land drained by a river and its tributaries.
What is the long profile of a river?
A diagram which shows how a river’s gradient changes through its different courses.
What is the cross profile of a river?
A diagram which shows what a cross-section of a river looks like in its different courses.
How does gradient change through the long profile?
Steepest gradient is in the upper course, more gentle in the middle course and very low-lying in the middle course.
How does velocity change through the long profile?
Velocity is low in the upper course due to friction with the river bed and banks. Increases in middle course; greatest in the lower course.
How does the channel change through the long profile?
Narrow and shallow in the upper course; uneven with rough surfaces. Becomes wider, deeper and smoother in middle course. Is widest, deepest and smoothest in lower course.
How does the river change through its cross profile?
Channel becomes wider and deeper in lower course. Valley becomes wider and flatter in lower course. Valley tends to be V-shaped in the upper course.
Why does the shape of the river’s cross profile change?
Erosion flattens and broadens the base of the valley. Weathering and mass movement make the valley sides less steep downstream.
What is the difference between vertical and lateral erosion?
Vertical erosion deepens the river bed, mainly occurs in the upper course and mainly by hydraulic action. Lateral erosion erodes river banks. More common in middle and lower courses of a river.
What is abrasion?
The action of boulders and stones wearing away the river bed and banks by scraping and grinding along them like sandpaper.
What is attrition?
Sediment knocking particles against one another and breaking them down into smaller, rounder pieces.
What is hydraulic action?
Fast-flowing water forcing air into cracks in the river bed and banks. Repeated changes in air pressure cause the bed and banks to weaken.
What is solution?
When slightly acidic river water dissolves soluble rocks such as chalk and limestone.
What is river transportation?
The movement of sediment/material by rivers. The material comes from weathered material that has rolled down hillsides and into rivers, as well as from eroded river bed and banks.
What is traction?
Large boulders and rocks rolled along the river bed.
What is saltation?
Small pebbles and stones bounced along the river bed.
What is suspension?
Fine, light material e.g. alluvium, carried along in the water. It floats along, hanging in the water.
What is solution?
When minerals dissolved in the water are carried along by the river’s flow, typically in areas where the bed and banks are made of soluble chalk or limestone.
What is deposition?
When material that was being transported by the river is dropped.
Why does deposition occur?
Because, sometimes, the velocity of a river decreases and it no longer has enough energy to transport material.
When does the velocity of a river decrease?
When the volume of water in the river falls. When the amount of eroded material in the water increases. When the water is shallower. When the river reaches its mouth.
Where is traction (transportation) dominant?
In the river’s upper course. Large, angular rocks tend to be transported here for a short time, mainly by traction, during periods of high flow.
Where is deposition dominant?
At the mouth of the river. The interaction with tides and the very gentle gradient greatly reduce the river’s velocity.
Which process dominates in the river’s upper course?
Vertical erosion.
What are interlocking spurs?
Fingers of land that jut out into the river valley.
How do interlocking spurs form?
The river cuts down vertically into the valley. If there are areas of hard rock in the valley, the river will flow around them (as they are harder to erode). This creates interlocking spurs of land, which link together like the teeth of a zip. They tend to have steep gradients and they project (stick out) from alternate sides of the valley.
What are rapids?
Fast-flowing, turbulent sections of the river where the river bed has a relatively steep gradient.
How do rapids form?
They form where there are alternate bands of hard and soft rock across the river channel. This leads to differential rates of erosion, resulting in an uneven river bed. Water pools in the deeper, more eroded areas and creates fast-flowing water.
What is a waterfall?
A sudden, steep drop in a river’s course.
How are waterfalls formed?
Formed where water rushes down steep hillsides in upland areas. Formed when there is a horizontal band of hard rock atop a horizontal band of soft rock. Soft rock is eroded quicker, creating a step. Differential erosion continues, undercutting the hard rock and forming an overhang. Overhanging rock, no longer supported, collapses into the plunge pool. Plunge pool, found at the base of the waterfall, is eroded deeper by hydraulic action & abrasion. Collapse of the overhang results in waterfall retreating upstream.
What is a gorge?
A steep-sided, narrow valley.
How does a gorge form?
Due to the continued retreat of a waterfall.
