Isostacy And Eustacy Flashcards
What is isostacy
The process whereby the land rises or falls relative to sea level.
What happens during isostacy
Glaciers weigh down the land
When they melt the surface returns back to its original place
When might isostacy also happen other than glaciers
When plates collide and the land uplifts
What is eustacy
The process whereby the sea levels rise or fall relative to the land
When does eustacy happen
During the id age rain and river water gets locked in ice sheets and does not reach the sea. This lowers the sea levels. When the ice melts large volumes of meltwater flow into the sea causing global rise
What are eustacy global changes called
Eustatic sea level changes
When does rejuvenation occur
When a rivers base level of erosion either rises or falls
Isostacys influences on rivers
What are the causes or rejuvenation
- Isostacy when land rises out of the sea due to tectonic activity raising the crust (isostatic uplift) may also occur when a great weight is removed eg melting of an ice cap. The land gradually rises due to the removal of the weight.
- When water is locked away in the ice caps it causes lowering of the sea level
What must occur for a river to be rejuvenated
A drop in sea level (isostacy/eustacy)
The rivers mouth is then higher above sea level and the river has further to travel before it reaches the sea.
This steeper gradient gives the river extra energy which enables the river to rejuvenate the process of vertical erosion.
Erosion processes starts to make a new long profile for the river.
What are the landforms of rejuvenation
Knickpoints
River terraces
Incised / entrenched meanders
What are knickpoints
Small waterfalls and Rapids that mark the point of rejuvenation on a rivers course after the land has risen out of the sea due to isostatic uplift.
Where does erosion in a knickpoint begin
At the booth of the river and works backwards by head ward erosion
What are river terraces
Flat steppened areas on each side of a river valley
They represent former flood plains
How do river terraces occur
As a result of rejuvenation verticals erosion renews the river to cut itself a new channel.
What are entrenched meanders
Steep sided meanders
