Glaciation – the accumulation of snow that turns into ice over many years. Over time this
flows down hill by gravity changing the landscape. For this to happen the temperature has
to drop so the snow and ice doesn’t melt.
It can change the land by 2 ways. It can physically rip out the rock or by large amounts of
water when the glacier melts.
Freeze thaw
This happens above the
glacier, but gives the
glacier “food” to rub
against other rocks.
Water freezes and
expands in cracks over
repetition of this process
the rock loosens and then
falls off into a scree or
talus slope.
Plucking
Plucking – like plucking a bird
– the feathers are grabbed and
ripped out, but the ice grabs
the rock and freezes around it.
As the glacier moves down hill
with gravity it rips the rock out.
Abrasion
When the glacier has rock in it
then it can wear the other rock
away by the action of rubbing
like sand paper
There are 2 types of features that you need to know about
Erosional Features
Corries (also called cwms in Wales and
cirques in the alps)
Arêtes
Pyramidal peaks
Hanging valleys
U-shaped valleys
Ribbon lakes and truncated spurs
Truncated spurs
Depositional Features
Terminal Moraine
Lateral and medial Moraine
Kettle holes
Eskers
Drumlins
Outwash plains
Glacial till/Boulder clay
Corries
1. Snow collects in a north facing slope and turns
onto a glacier
2. Glacier moves down hill by gravity
3. As it moves it plucks on the sides of the glacier –
this steepens the back wall
4. Plucking is where the glacier freezes round a
rock and is then ripped out as the glacier moves
down hill
5. Also abrasion occurs under the glacier
6. Abrasion is like sand paper – rock and ice
through the weight of the glacier abrades the
bottom of the corrie
7. Back wall is also steepen through freeze thaw –
this occurs above the glacier and continues to
steepen when the glacier has melted
8. The bottom of the corrie is over deepened by
abrasion as the glacier is at its deepest at this point; this often leaves a corrie lip
9. Often a lochan/tarn is left behind.
Arêtes
1.
2.
3.
4.
A narrow ridge between 2 corries
As the corries move downhill by gravity
Steep sides are created from plucking by the glacier
Plucking is where the glacier freezes round a rock and is then
ripped out as the glacier moves down hill
5. The floor is deepened by abrasion - Abrasion is like sand paper –
rock and ice through the weight of the glacier abrades the bottom of the
6. Over time the 2 corries push back
7. This creates a knife edge ridge between the 2 corries and this is called
a arête
8. Freeze thaw continues to steepen the walls after Glaciation
Pyramidal Peaks
1. This is a steep peak that is surrounded by 3 or more corries
2. Each corrie abrades the floor by rubbing the bottom with moraine
held within the glacier and making the corrie floor lower
3. The corries also pluck the back wall this is where the glacier
freezes to the rock and rips it out, this leaves
steep walls leading to the summit
4. Freeze thaw happens above the glacier both
during and after glaciation this increases the
steepness of the back wall
Hanging valleys
1. A hanging valley is formed where 2 glacier meet as they travel down
hill by gravity
2. One glacier is bigger than the smaller glacier
3. The big glacier has a greater capacity for downward erosion as it is
heavier
4. The glaciers abrade the floor widening the valley floors by rubbing
moraine held within the glacier along the floor
5. It steepens the sides of the valleys by freezing to the rock and as it
moves downhill by gravity it rips out the rock this is called plucking
6. When the glaciers have melted the smaller valley is left hanging above the
bigger glacier with a steep drop often with a waterfall.
U-shaped Valley/Mis-fit Stream/Ribbon Lake
1.
2.
3.
4.
Glacier moves down hill by gravity
As it does so it plucks the valley sides by freezing to it and ripping out the rocks
This steepens the valley sides
Additionally material called moraine that is carried within the glacier abrades the
valley floor by rubbing along the bottom of the valley
5. This widens and deepens the valley floor
6. If the valley fills in with water it becomes a ribbon lake
7. If a small river flows down the valley it is called a misfit stream as it
could not have created the valley it is flowing down