Alteration of the Valley
Glaciers, moving downhill from their source in the mountains, follow the easiest route; this generally tends to be the route of an existing river channel. Unlike a river, a glacier often fills the whole valley, giving it greater erosive power. Instead of having to wind around obstacles, such as interlocking spurs, the glacier is able to widen, deepen and straighten the valley through abrasion. This results in V shaped valleys being turned into U shaped ones and the removal of interlocking spurs, leading to cliff like truncated spurs.
Click here to open a field sketch showing how a valley can be converted from a V to a U shape.
U shaped valley
Between adjacent truncated spurs are hanging valleys. Before the ice age, tributary rivers would have flowed at the same height as the main channel. During the ice age, the enormity of the glacier following the course of the main channel will have eroded the valley floor more quickly than would have occurred in the tributary rivers. This has led to tributary rivers now entering the main channel by a waterfall.
To see an example click here.
Hanging valley
Ribbon lakes are produced due to erosion, when a glacier deepens an area of the valley more than the rest, probably due to the presence of softer rock. They can also be created due to the deposition of moraine across the main valley.
To see an example click here.
What is moraine?
Moraine is angular material that is transported and then deposited by a glacier. When temperatures rise the ice begins to melt and can no longer hold onto as much material, as the material is deposited different features are formed.
What is an Erratic?
Erratics are foreign pieces of rock found in previously glaciated areas. This basically means they have been found in an area they are known not to originate from.
What is a Drumlin?
A drumlin is another kind of feature formed due to the deposition of material once carried by a glacier.
Drumlins appear as elongated hills; they can be over 1 kilometre long, half a kilometre wide and 150 metres high.
