Deposits laid down by ice are called till or boulder clay which is an assortment of material of various shapes and sizes. Boulder clay can be found in areas of the UK such as Lincolnshire and East Anglia. It is easily eroded, and is one reason why the Holderness coast is so vulnerable to wave attack.
Drumlins and erratics
An erratic in Crummackdale
Unlike river deposits that are often sorted into different sizes, all glacial deposits are angular and mixed up (unsorted). The extreme of this can be seen in erratics. These are large rocks or boulders that are often found on their own, rather than in piles. They are unusual shapes, unusually large and of a rock type uncommon to the area they have been dumped, eg the Norber erratic.
Vale of Eden in the Lake District
Drumlins are elongated hills of glacial deposits. They can be 1 km long and 500 metres wide, often occurring in groups. A group of drumlins is called a drumlin swarm or a basket of eggs, eg Vale of Eden. These would have been part of the debris that was carried along and then accumulated under the ancient glacier. The long axis of the drumlin indicates the direction in which the glacier was moving. The drumlin would have been deposited when the glacier became overloaded with sediment. However glaciologists still disagree as to exactly how they were formed.
Diagram plan of a drumlin
When glacial ice melts, different types of rock are laid down that have been carried along by the glacier. Piles of these deposits are called moraines.
Different types of moraine
- Terminal moraines are found at the terminus or the furthest (end) point reached by a glacier.
- Lateral moraines are found deposited along the sides of the glacier.
- Medial moraines are found at the junction between two glaciers.
- Ground moraines are disorganised piles of rocks of various shapes, sizes and of differing rock types.