What is a Drumlin?
Drumlin's meaning is quite simple. Drumlins are elongated, oval-shaped or say teardrop-hills of rock, sand, and gravel. A drumlin is by and large made up of glacial drift, formed underneath an ice sheet or moving glacier and oriented in the direction of ice flow. There are no strict specifications with respect to the size of a drumlin but they tend to be up to a few kilometers up to 2 kilometers long and up to 50m in relief.
How Do Drumlins Form?
Drumlin glacier develops in the form of clusters apparently close to the terminus of glaciers. The mechanisms of formation are though disputed. They seemingly have significant interpretive value for rate and direction of glacial movement.
Drumlins are usually found in wide-ranging lowland regions, with their long axes approximately parallel to the path of glacial flow. Though they are observed in a multitude of shapes, the glacier side is always steep and high, while the lee side is tapered and smooth mildly in the direction of ice movement. Drumlins can hugely differ in size, with lengths from 1 to 2 km, heights from 50 to 100 feet, and widths from 400 to 600 m.
Regions of Formation of Drumlins
They are extensive in formerly glaciated regions and are particularly copious in Canada, Finland, Ireland, and Sweden.
Besides, Drumlins are mostly found in clusters with their numbering counting in the thousands. Often organized in belts, they impede drainage such that the small lakes and swamps may form between them. Large drumlin fields are situated in central New York and central Wisconsin; in northwestern Canada; and southwestern Nova Scotia.
Composition of Drumlins
Most drumlins are made up of till, but they may differ largely in their composition. Some contain substantial amounts of gravel, whereas others are composed of rock underlying the till surface (rock drumlins). Drumlins are most commonly linked with smaller, glacially streamlined bedrock forms referred to as roches moutonnées.
Eskers
Eskers are the geological structures that are formed when the glacial melted water carries the sediments and deposit through subglacial tunnels. Thus, they can give relevant information with regard to the shape and dynamics of glaciers and ice sheets whereas Drumlins are developed when the ice sheets move in streamline over the rock residue. These are elongated, oval shaped hills.
Drumlins and Eskers
Drumlins and Eskers by definition may seem similar, but there are still certain differences that you need to know about. These are as follows:-
Bedrock
Bedrock, the sediment of solid rock which is essentially buried beneath the soil and other splintered or segregated substances (regolith). Bedrock is composed of igneous, metamorphic or sedimentary rock, and it often caters to as the parent substance (the source of rock and mineral particles) for soil and regolith. In Earth’s nitrogen cycle, bedrock is also a source of nitrogen. A bedrock accumulation which takes place at Earth’s surface is known as an outcrop.
FAQs on Drumlin
1. What is a drumlin and how is it formed?
A drumlin is an elongated, teardrop-shaped hill formed by glacial ice acting on underlying unconsolidated material. They are primarily formed beneath moving glaciers. As a glacier flows over sediment (glacial till), it can mould it into this distinctive shape. The blunt, steep end (stoss) faces the direction from which the ice came, while the gentle, tapered end (lee) points in the direction of the ice flow.
2. What are the key characteristics used to identify a drumlin?
Drumlins are identified by a specific set of characteristics:
Shape: An asymmetrical, elongated oval or teardrop shape, often described as a 'whaleback'. When found in groups, they create a 'basket of eggs' topography.
Orientation: All drumlins within a field are aligned parallel to each other, indicating the direction of past glacial movement.
Profile: They have a steeper, blunter slope (stoss side) facing the upstream direction of ice flow and a gentler, tapering slope (lee side) on the downstream side.
Composition: They are typically composed of glacial till, which is an unsorted mix of clay, silt, sand, gravel, and boulders.
3. What is the difference between a drumlin, a moraine, and an esker?
While all are landforms created by glaciers, they differ significantly in shape, composition, and formation process:
Drumlin: An elongated hill of glacial till moulded under a moving glacier, with its long axis parallel to the direction of ice flow.
Moraine: A ridge or mound of unsorted glacial debris (till) that is deposited at the edges or end of a glacier. Moraines mark the glacier's boundary, not the flow direction underneath it.
Esker: A long, winding ridge of sand and gravel. It is formed by meltwater streams flowing within or under a glacier, depositing sediment in their channels.
4. What are drumlins primarily composed of?
Drumlins are predominantly made of glacial till, which is a poorly sorted mixture of sediments directly deposited by a glacier. This till includes a wide range of materials from fine clay and silt to larger sand, gravel, and boulders. In some instances, a drumlin may have a core of bedrock or older sediments that the glacier has streamlined and then covered with a layer of till.
5. What do drumlins reveal about the glacier that created them?
The presence and orientation of drumlins provide crucial information about the paleoglacier (a former glacier). The uniform alignment of drumlins in a field acts as a clear indicator of the direction of ice movement on a regional scale. The tapered lee slope always points in the direction the glacier was flowing. Their shape can also provide insights into the flow conditions, such as whether the ice was advancing quickly or was 'warm-based' (with meltwater at its base), allowing it to slide and deform the sediment beneath it.
6. Are drumlins considered depositional or erosional features?
This is a topic of debate among geologists, and drumlins are often described as having both depositional and erosional characteristics. The most widely accepted theories suggest they are primarily depositional, formed by the plastering or accretion of sediment under the ice. However, some theories propose that they could be erosional remnants of a pre-existing landscape that was streamlined by the overriding glacier. Most modern interpretations suggest it is a combination, where a glacier both erodes and deposits material to create the final streamlined shape.
7. What are the main theories explaining the formation of drumlins?
The exact formation of drumlins is still a subject of scientific research, but several key theories exist:
The Deforming Bed Model: This is the most widely accepted hypothesis. It suggests that as a glacier moves over a bed of weak, water-saturated sediment, it deforms and moulds this material into streamlined hills.
The Accretion Theory: This theory proposes that drumlins are built up layer by layer as a glacier deposits till around a small nucleus, such as a boulder or a patch of frozen ground.
The Flood Hypothesis: A more catastrophic theory suggests that drumlins were formed rapidly by massive subglacial meltwater floods.
8. Where are some famous examples of drumlin fields located in the world?
Drumlins often occur in large groups called drumlin swarms or fields. Some of the most well-known examples can be found in regions formerly covered by ice sheets:
North America: In Wisconsin, Minnesota, and New York (USA), and Ontario (Canada).
Europe: Across much of Ireland (especially Clew Bay), the Lake District in England, and parts of Germany, Poland, and Finland.
