Today we are going to talk about a type of geological formation that is formed from the glacial relief. Its about drumline. This name comes from the Irish "droim" or "drim" and means "crest of a hill". Its formation comes from the glacial reliefs and it is nothing more than a small mound with smooth slopes that is shaped like a lying whale. They are generated from the modeling of a glacier in the direction of ice movement in times of glaciation.
In this article we are going to tell you all the characteristics, training and curiosities of the drumlin.
Key features
We are talking about a type of small mound that is composed of smooth slopes. The smooth slopes have this texture since the ice of the glaciation and the periods of thaw causes erosion by abrasion. The shape of the drumlin is that of a lying whale and is generated by the direction of movement predominantly carried by ice during ice ages.
Because drumlins are found alongside moraine deposits, they are considered formations from a moraine that forms at the bottom of a glacier. Moraines are the set of glacial sediments that accumulate on the sides of a glacial structure. They can appear in isolation but are more frequently found in groups. occurs in the Chilean Patagonia area. The sediments that form moraines move in the direction of the ice with the prevailing wind. We know that ice also has its own movement depending on the slope and periods of glaciation. To better understand these processes, you can consult our article on What are moraines?.
Formation of a drumlin
Let's see what is the process by which the drumlin is generated. We know that they are part of a landscape that is shaped by the action of a glacier. There are numerous debates about the origin of the drumlin, although the theories most affected are the following:
- It is the product generated through a flood under a glacier. This alluvium is capable of transporting a lot of material at a single moment and accumulates in the channels of the sub-ice. These channels are where the water flows, which freezes, but from the lower part also continues in a liquid state. We know that the ice is stuck to the sediment but it is not completely frozen. The lower part of the ice that is rotating the sediments and the ground is usually in a liquid state and is responsible for the movement of the ice.
- Formed by a very large glacial ice sheet that was gradually scratching the earth's surface. When we refer to scratching the earth's surface we are referring to a type of erosion called abrasion. Abrasion is the process that is generated through the dragging of sediments and the weight of each one. In other words, when ice creeps across a surface, it generates abrasion due to its structure and the soil is eroded and has a smooth texture.
The formation of a drumlin is associated with the type of material that makes up these hills. The permeability of the sediments seems to play an important role in the shaping process. If the sediments beneath the ice accumulated during periods of snowfall are permeable, it is more difficult for the ice to be dragged, as it will seep in. If you want to learn more about the glacier modeling, I invite you to consult our article.
Drumlin materials
Let's see what are the main materials that a drumlin was made of. The first of all is to know what is composed of glacial mud. This glacial mud is known by the name of till. It is a mixture of clay, sand, and gravel with angular edges and sometimes blocks of rock. The glacier drags and pushes these materials, depositing them at the bottom. This material was thus available for transport by the glacier's low alluvium.
Sometimes, sediment can form a drumlin, generated by the movement of water through rivers that flow beneath the ice. As we mentioned before, beneath the layer of ice lies a layer of liquid water, like a river. Very rarely, the ice is completely frozen. Especially during the melting season, the part that turns liquid most quickly is the interior of the ice. In this case, when the drumlin forms by The rivers that circulate under the ice are composed of pebble gravels.
Forms of accumulation
Since the last glaciation, approximately 18.000 years ago, the ice has been retreating, exposing inherited reliefs throughout the area occupied during the previous glaciations. In other words, the melting of ice and the reduction in the surface area covered by it reveal a relief modeled with glacial patterns.
The glacial deposits known as till are sediments composed of materials deposited directly by glaciers. These materials do not have stratification and their fragments show striations as a result of displacement and friction with the ground. The moraines are formations composed of tills that accumulate on the sides of the glaciers. If the glacier recedes a layer of wavy-shaped tills called the basal moraine is deposited. Once the front continues to retreat, it can stabilize and form a retreat moraine. To learn more about the formation of these deposits, see the article on glaciers.
Lateral moraines are more typical of valley glaciers. They are responsible for transporting all sediment along the margins of the glacier and are deposited in long ridges. When lateral moraines join at the confluence of two valleys, a central moraine is formed.
Finally, once the sediments have been deposited outside the glacier surface and carried by the wind and the action of other geological agents, the drumlin is formed. There are other geomorphological formations resulting from glacial relief and which are composed of stratified debris and are the kame, kame terraces, and the eskers.
I hope that with this information you can learn more about the drumlin and its characteristics.