Subglacial depositional landforms - Drumlins Flashcards
What are drumlins?
Drumlins are large oval-shaped hills, largely composed of glacial till, formed beneath a glacier or ice sheet and aligned in the direction of ice flow.
Describe the shape of drumlins?
Drumlins have a smooth, elongated and asymmetric shape.
Describe the size of drumlins?
Drumlins vary in size from 5 to 50m high and from 10 to 3,000 meters long.
What are drumlins usually found in?
Drumlins are usually found in groups or ‘swarms,’ forming ‘basket of eggs’ topography.
Where are drumlins usually located?
Drumlins are typically located in lowland areas such as County Down, Northern Ireland, in close proximity to upland areas where there is a high supply of basal debris.
The majority of drumlins in a swarm have their highest elevation and blunter end pointing in which direction?
The majority of drumlins in a swarm have their highest elevation and blunter end pointing in an upstream direction.
Where does the more gently sloping tail of the drumlin usually face?
The more gently sloping tail of the drumlin usually faces down-ice.
What is the upstream blunt end of the drumlin called?
The upstream blunt end of the drumlin is called the stoss end.
What is the downstream end of the drumlin called?
The downstream end of the drumlin is called the lee end.
What is a common measure of the drumlin’s shape?
A common measure of the drumlin’s shape is the elongation ratio, which is the maximum drumlin length divided by the maximum width.
What impact did the speed of ice flow have on the elongation ratio of the drumlin?
The faster the ice was flowing, the greater the elongation ratios.
Drumlins are likely to be polygenic in origin. What does this mean?
Drumlins are likely to be polygenic in origin. This means that they were created by any of a range of processes.
What is the concept of equifinality?
Equifinality - The concept that the same landform may result from very different sets of processes in varying contexts.
How do drumlins differ?
Some drumlins have rock cores surrounded by till. Others comprise unconsolidated sediments that are poorly sorted, whilst some have fluvially sorted sediments demonstrating that fluvial deposition was a part of the drumlin formation process.
Describe the two main theories regarding the formation of a drumlin?
- As ice overrode subglacial till, it moulded the material into elongated shapes, with their long axes orientated in the direction of flow
- Subglacial meltwater scoured cavities in the base of the ice; these cavities were subsequently filled with subglacial sediments and finally moulded into drumlins by advancing ice
