A depositional landform is a landform that is created from glacial deposition. This is when a glacier carries some sediment, which is then placed (deposited) somewhere else. This could be a large group of glacial sediment or a single significant material.
Explore our app and discover over 50 million learning materials for free.
Lerne mit deinen Freunden und bleibe auf dem richtigen Kurs mit deinen persönlichen Lernstatistiken
Jetzt kostenlos anmeldenNie wieder prokastinieren mit unseren Lernerinnerungen.
Jetzt kostenlos anmeldenA depositional landform is a landform that is created from glacial deposition. This is when a glacier carries some sediment, which is then placed (deposited) somewhere else. This could be a large group of glacial sediment or a single significant material.
Depositional landforms consist of (but are not limited to) drumlins, erratics, moraines, eskers, and kames.
There are many depositional landforms, and there is still some debate on which landforms should qualify as depositional. This is because some depositional landforms come about as a combination of erosional, depositional, and fluvioglacial processes. As such, there is no definite number of depositional landforms, but for the exam, it is good to remember at least two types (but aim to remember three!).
Here are some brief descriptions of different types of depositional landforms.
Drumlins are collections of deposited glacial till (sediment) that form under moving glaciers (making them subglacial landforms). They vary greatly in size but can be up to 2 kilometers long, 500 meters wide, and 50 meters in height. They are shaped like half a teardrop rotated 90 degrees. They are usually found in large groups known as drumlin fields, which some geologists describe as looking like ‘a large egg basket’.
Terminal moraines, also known as the end moraine, are a type of moraine (material left behind from a glacier) that form at the edge of a glacier, a prominent ridge of glacial debris. This means that the terminal moraine marks the maximum distance a glacier travelled during a period of sustained advance.
Erratics are usually large stones or rocks left behind/dropped by a glacier either due to chance or because the glacier melted and started retreating.
What distinguishes an erratic from other objects is the fact that the composition of the erratic doesn’t match anything else in the terrain, which means that it is an anomaly in the area. If it is likely that a glacier carried this anomalous object, it is an erratic.
Let’s see how useful drumlins are in reconstructing past ice movement and ice mass extent.
Drumlins are very useful depositional landforms for reconstructing past ice movement.
Drumlins are oriented parallel to the movement of the glacier. More importantly, the drumlin’s stoss end points upslope (direction opposite glacial movements), whilst the lee end points downslope (direction of glacial movement).
Note that this is opposite to roches moutonnées (see our explanation on Erosional Landforms). This is due to the different processes that created the respective erosional and depositional landforms.
Since the drumlin is made up of deposited glacial sediment (till), it is possible to conduct till fabric analysis. This is when the movement of the glacier influences the sediment it runs over to point in the direction of its movement. As a result, we can measure the orientations of a large number of till fragments to inform the reconstruction of the direction of glacial movement.
One more way drumlins help reconstruct past ice mass movement is by calculating their elongation ratio to estimate the potential rate at which the glacier was moving through the landscape. A longer elongation ratio suggests faster glacial movement.
When it comes to using drumlins for reconstructing ice mass extent, there are some problems.
Drumlins suffer from what is called equifinality, which is a fancy term for: ‘we don’t know for sure how they came about’.
Another issue is that drumlins have been altered and damaged, mostly due to human actions:
Very simply, yes. Terminal moraines can give us a great indication of how far a past glacier travelled in a given landscape. The position of the terminal moraine is the final boundary of the glacier’s extent, so it can be an excellent way to measure the maximum past ice mass extent. However, two potential issues can impact the success of this method:
Issue one
Glaciers are polycyclic, and this means that in their lifetime, they will advance and retreat in cycles. It is possible that after a terminal moraine is formed, a glacier will once again advance and surpass its previous maximum extent. This leads to the glacier displacing the terminal moraine, forming a push moraine (another depositional landform). This can make it tough to see the extent of the moraine itself, and so it is difficult to determine the maximum extent of the glacier.
Issue two
Moraines are susceptible to weathering. The edges of terminal moraines can undergo intense weathering due to harsh environmental conditions. As a result, the moraine can appear shorter than it was originally, making it a poor indicator of past ice mass extent.
If we can identify the origin of the erratic, then it is possible to trace the general direction of the past glacier that deposited the erratic.
Suppose we mark the origin of an erratic point A on a map and its current position as point B. In that case, we can draw a line between the two points and align it with either a compass direction or bearing in order to find a very accurate direction of past ice mass movement.
However, this method in the example doesn’t capture the exact movements the glacier may have taken, but for practical purposes, these movements don’t matter much.
Unlike the other depositional landforms mentioned here, erratics face few issues when reconstructing past ice mass movement. But what if we can’t identify the origin of the erratic? No problem! We can argue that if we can’t identify the origin of an erratic, then it’s likely it wasn’t deposited by a glacier – meaning it wouldn’t be suitable to call it an erratic in the first place.
Depositional landforms consist of drumlins, erratics, moraines, eskers, and kames.
A depositional landform is a landform that is created from glacial deposition. This is when a glacier carries some sediment, which is then placed (deposited) somewhere else.
There are many depositional landforms, and there is still some debate on which landforms should qualify as depositional. This is because some depositional landforms come about as a combination of erosional, depositional, and fluvioglacial processes. As such, there is no definite number of depositional landforms.
Three depositional landforms (which are very useful to learn for discussing the possibility of reconstructing past ice mass movement and extent) are drumlins, erratics, and terminal moraines.
Why is there an issue with using drumlins to recreate past ice mass extent?
Due to equifinality: we don’t know the exact process by which drumlins are formed, so we can’t make definite claims as to how a drumlin is indicative of past ice mass extent.
Describe how two depositional landforms may be used to recreate ice mass extent of movement
Mapping the journey of an erratic and finding the endpoint of a terminal moraine.
Explain why terminal moraines could be misleading when using them to reconstruct past ice mass extent.
Due to the polycyclic nature of glacial movement, a terminal moraine could be the endpoint of just one period of glaciation. In another period, a glacier could move past it and form a push moraine.
What is an erratic? How can we differentiate an erratic from any other stone or rock in an area?
An erratic is a rock or other piece of matter that is uncommon in the rest of the surrounding geology (i.e. it does not make sense that it would have formed in the location it is found). As a result, it was likely deposited in that area by a glacier, making it an erratic.
Name two ways drumlins can indicate past ice mass movement.
Drumlins can indicate past ice mass movement via their stoss and lee slopes. Till fabric analysis can also be done.
In which directions do a drumlin's stoss and lee slopes point?
The lee slope points in the direction of glacial flow (downslope) and the stoss slope is against the glacial flow (upslope).
Already have an account? Log in
Open in AppThe first learning app that truly has everything you need to ace your exams in one place
Sign up to highlight and take notes. It’s 100% free.
Save explanations to your personalised space and access them anytime, anywhere!
Sign up with Email Sign up with AppleBy signing up, you agree to the Terms and Conditions and the Privacy Policy of StudySmarter.
Already have an account? Log in
Already have an account? Log in
The first learning app that truly has everything you need to ace your exams in one place
Already have an account? Log in