Rejuvenation Flashcards
When does rejuvenation occur? 2
- A fall in sea level relative to the level of land
2. The rise of land relative to the sea.
What does rejuvenation allow the river to do?
Renew its capacity to erode as its potential energy increases.
What landforms may be formed as a result of rejuvenation, and when?
Knick points, waterfalls and rapids, river terraces, entrenched and incised meanders.
When the river attempts to regrade its profile to a normal concave shape.
What is rejuvenation? KEYWORD
An increase in the energy of a river caused either by a fall in base level or an uplift in land.
What is an incised meander? KEYWORD
Caused by rejuvenation.
A meander that has cut deeply into the floodplain, creating steep cliff-like banks.
What is a river terrace? KEYWORD
A narrow, flat piece of ground that runs parallel to the river on either side, above the level of the floodplain. They are usually created following a fall in base level.
What is a knick point? KEYWORD
Usually marked by rapids, this represents rejuvenation and is a sudden break in the long profile of the river.
Explain a knick point.
Sudden break in the gradient along the long profile of a river.
Sharply defined e.g waterfalls, or barely noticeable.
Headward erosion cuts the profile down to sea/base level.
Knick points mark where this process has reached upstream.
Explain a river terrace.
+ EXAMPLE
Lower course.
It’s a remnant of a former floodplain, which has been left at a higher level after rejuvenation of the river.
If vertical erosion is rapid then paired terraces are formed either side of the channel.
If vertical erosion is slower though, unpaired terraces form as the river is given opportunity to meander.
EXAMPLE: River Thames.
What are incised meanders?
If a rejuvenated river occupies a valley with well-developed meanders, renewed energy results in them becoming incised or DEEPENED.
E.g. The British Isles.
Two types of incised meanders: ingrown and entrenched.
What is an ingrown meander?
+ EXAMPLE.
Slow incision and lateral erosion occurs.
Asymmetrical valley.
Steep cliffs on the outer bends.
Gentle slip-off slopes on the inner bends.
EXAMPLE: Snake River Canyon.
What is an entrenched meander?
+ EXAMPLE.
Rapid incision and vertical erosion occurs.
Symmetrical valley.
Steep sides.
Gorge like appearance.
EXAMPLE: City of Durham is built inside an entrenched meander.
What is the base level?
The lowest point to which the river can flow - the ‘mouth of the river’.
What causes sea levels to change?
- Isostatic - local changes where the height of the land changes relative to the global sea level e.g. glaciation. The ice weight can depress the crust, causing the land to fall relative to the level of the sea.
Ice gone in warmer periods - land rebounds upwards - rising relative to the level of the sea e.g. Scotland. - Eustatic - global change in sea level - temperature of the Earth.
Warmer periods - less ice - warmer water - expands - sea levels rise.
Colder periods - contracts - sea levels fall.
What happens as a result of falling sea levels?
Raised beaches, abandoned cliffs, erosion surfaces etc.
The graded river profile is no longer in balance.
More energy at the mouth and vertical erosion (usually would occur at the source).
