Formation of a Corrie
A corrie looks rather like a
armchair has been cut out of
the rock face
When a hill has been heavily
eroded with 3 or 4 corries the
jagged hill that is left is known
as a pyramidal peak.
Large
crevasse
Plucking occurs
when the ice begins
to stick to the rock
Formation of the Corrie
Freeze thaw affects the back wall, so here
rocks that become loose from cracking begin
to break off.
Abrasion occurs
when the rocks are
scraped along the
base of the rock
Often two or more corries are
formed leaving a narrow ridge
between them. This narrow ridge is
called an arête
This ice that is also stuck to the back wall
begins to pluck off rock when it moves
At the bottom of the hollow piece of rock
abrasion starts to occur. So the hollow gets
worn down by the sandpaper effect making it
deeper.
When the glacier leaves the hollow you are
left with a corrie.
Formation of a Ribbon Lake
A ribbon lake is a long and
narrow, finger-shaped lake
Formation of a Ribbon Lake
When the glacier picks up rocks when
moving the process of abrasion begins
to occur
The ribbon lake is usually found in a
glacial trough
This sandpaper effect starts to wear
away the softer rock faster than the
hard rock
This creates a hollow in the rock
called a rock basin
Over time as the ice melts and from
rainwater the basin starts to fill with
water
Creating a Ribbon Lake
For a ribbon lake to form
there needs to be an area of
soft rock, usually between
hard rock
Formation of a Tarn
A Tarn is a lake that is formed when a
glacier is excavated (moves from) a
corrie. The water left behind is called
a Tarn.
So without the formation of a
corrie a tarn would not be formed
Formation of the Tarn
Freeze thaw affects the back wall, so here rocks that become
loose from cracking begin to break off.
This ice that is also stuck to the back wall begins to pluck off
rock when it moves
At the bottom of the hollow piece of rock abrasion starts to
occur. So the hollow gets worn down by the sandpaper effect
making it deeper.
When the glacier leaves the hollow you are left with a corrie.
Water that is left by the glacier forms a lake called a tarn in
the hollow rock
Tarn
Formation of an Arête
An arête is a thin, almost knifelike, ridge of rock
They occur at the
mountain top
An arête can be formed in two separate ways…..
Formation can occur when two u shaped valleys are parallel to one another (side by
side) and they have both been eroded by the path of glaciers
As the glaciers move they create a deep U shaped valley with steep sides. The ridge
between the two valleys is very thin and sharp and is named an arête.
The second way an arête can be formed is when two corries are eroding back to back
towards each other. The steep back walls meet creating a steep and sharp ridge. This is
called an arête.
Formation of a Pyramidal Peak
A Pyramidal Peak is the peak of a
mountain shaped like a pyramid formed
this way by glacial erosion
When three corries occur in the same place in a back to back arrangement
a Pyramidal Peak can be formed
When there are three or more of these corrie back walls and arêtes
joined together to form a single peak it creates a pyramid shape with very
steep walls, this is called a pyramidal peak
They are a common shape for mountain tops in glaciated areas.
Imagine the pyramids
of Egypt only with
armchair shapes cut
into them
Formation of a Hanging Valley
Formation of a hanging valley
Water once flowed down the mountain sides in small
tributaries/streams and joined the river in the main valley
The stream falls from a
smaller valley into the
main valley, this is how it
got the name hanging
valley
Over time a glacier erodes the valley making the valley
deeper and deeper until the smaller valleys joining the main
valley are much higher
This means that when the water from the streams comes
down the smaller valleys it has to drop from one valley into
the river below
This is described as a hanging valley
A glacial trough is a steep U shaped
valley left behind by the erosion of a
glacier
Formation of Glacial Trough
As we know glaciers follow the
paths of rivers
We also know that a very large
piece of ice called a glacier is
very, very strong
So if we had a river which had many turns and bends in the power of
the glacier would in time over ride this.
So your river would look like
this and after glacial erosion
look like the picture on the
right
What is meant by this is that the glacier will plough through the rock
making the river straighter and wider, shall we say taking the easiest
route by using sheer force