Glacial Erosion

If you hold some ice, it's pretty smooth, right? Well, glacial ice isn't. It's often full of rocks and other materials that rub against the mountainside, grinding away, making some interesting marks on the landscape. Let's learn about how ice can shape landscapes and what kind of landforms can still be seen today as a result of glacial erosion. This explanation goes hand in hand with the Glacial Depositional Landforms explanation, as well as our explanations on Glacial Landscapes, Glacial Landforms and Glacial Processes, so don't forget to read all of those too! They will give you a firm understanding of the topic we are learning about today! If you haven't read these, you might come across some words you don't know in this explanation! So, what are the types of glacial erosion? What landforms are created by these processes? Let's dive in!

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    Types of glacial erosion

    Ice is a pretty powerful thing, and through the physical process of erosion, particular landforms can be created. We'll talk more about these landforms later on, but first, let's understand what the process of erosion is, and the different types of glacial erosion that take place in glacial environments.

    Erosion is when materials are scraped away by something (in this case, ice), bringing the broken material along with it as it moves.

    During a glacial period, the power of gravity can pull glaciers down mountainsides, and as they move, the process of erosion takes place, i.e., as the ice moves, it scrapes against the mountainside. There are actually a couple of different erosion processes, so let's take a look at them.

    Abrasion

    This type of erosion occurs when there are rocks of all shapes and sizes inside a glacier. As a glacier moves downwards, these rocks scrape on the rocks underneath, eroding them away. Think of when you use sandpaper on some wood; it's a similar kind of action.

    Striations occur when glaciers erode the rock by abrasion, scraping grooves into the rock below. Striations are fascinating characteristics of the landscape, as they can show what direction the ice was flowing in, and at what points it was flowing from.

    Plucking

    As the ice is moving over a mountainside, some of the rocks can be looser than others; this allows meltwater to make its way underneath those loose rocks.

    Meltwater is, quite literally, the melted water from ice or snow. This meltwater can make its way to the bottom of a glacier through big cracks in the ice.

    As this meltwater freezes, it allows the loose rock to break away, or, it's plucked off the mountainside, as the ice continues its movement downwards.

    Another important physical process, that is similar to erosion, is weathering. In terms of glaciation, the process of freeze-thaw weathering is worth mentioning. Now, with erosion, the materials that are eroded are actually carried away with the ice. Weathering, however, wears the rock away, without actually moving the rock anywhere. Freeze-thaw weathering causes rocks to be broken by the expansion of frozen water and pressurisation. For more information on the process of freeze-thaw weathering, take a look at the Glacial Processes explanation.

    Glacial landforms caused by erosion

    Now, we've just discussed how ice can erode a landscape. But surely that can't be the end of it, right? Absolutely not! These processes of erosion have the power to create fascinating landforms, which are features seen on glaciated landscapes today. Let's take a look at these glacial landforms caused by erosion.

    Landforms of glacial erosion definition

    What exactly is the definition of landforms of glacial erosion? Well, as the processes of abrasion, plucking, and freeze-thaw weathering occur, they can create certain things or distinct marks that stand out on a landscape. These landforms can include things like lakes, peaks, or landforms with interesting names like arêtes. Let's explore some of these landforms, their characteristics, and their formation, and offer some examples along the way!

    Corries

    No, we're not talking about Coronation Street! Corries, also known as cwms or cirques, are usually at the start of a glacier. It's a big dip in the mountainside, which snow can fall into over time. As more time passes, the snow becomes so compressed, that it eventually turns into glacial ice. Through the processes that we spoke about earlier, like abrasion, plucking, and even freeze-thaw weathering, the big dip gets bigger! This ice is seemingly trapped in this dip in the mountainside, but fascinatingly, the power of gravity still allows the glacier to move; this movement is called rotational slip. When the ice eventually melts after a glacial period, a small lake is left behind, called a tarn. A great example of a corrie can be seen at Helvellyn, in the Lake District.

    Arêtes and pyramidal peaks

    Arêtes are when two corries are formed on either side of each other, creating a kind of spiky ridge between the two. If you have two eroding glaciers on either side, that ridge is going to become sharper and steeper! Add another corrie into the mix on another side of the mountain, alongside the arête, and a pyramidal peak will form. With increasing erosion, the peak will become more and more pointy.

    Glacial Erosion Arête with snow StudySmarterFig. 1 - the Carn Mòr Dearg arête, Scotland

    U-shaped valleys/glacial troughs

    On a non-glaciated mountain landscape, rivers flow down mountainsides, eroding as they make their way down, typically creating a 'V'-shaped valley. (You'll learn about this in the explanations on rivers!) As ice became dominant, it found its way into these valleys from the expansion of small corries and was able to erode these valleys further. Through plucking and abrasion, as well as the sheer power of the ice, a U-shaped valley, or glacial trough, is formed. These valleys are typically incredibly deep, with steep valley sides.

    Glacial Erosion Landforms U-shaped Valley with a house in the middle StudySmarterFig. 2 - U-shaped valley in Grey Mare's Tail, Scotland

    Hanging valleys

    Tributaries are smaller streams that lead to or from rivers. In non-glaciated times, these tributaries would flow down the valley sides to meet the river at the bottom of the valley. With ice presence, as the ice erodes down the mountain, it leaves these tributaries behind on the steep valley sides, ending pretty sharply. They are essentially left hanging. Once the ice melts, waterfalls from those tributaries fall from sky-high into the U-shaped valley, forming a hanging valley.

    Truncated spurs

    On a river landscape, interlocking spurs are a major characteristic. As a river flows, it erodes different types of rocks differently, depending on whether they are easy or hard to erode. This creates a kind of zigzag in the landscape, known as interlocking spurs. During a glaciated period, the sheer power of the ice, cuts right through these spurs, creating truncated spurs.

    Ribbon lakes

    Glaciers erode the landscape as they move. However, some of the rock may be softer than others, which means glaciers can erode these more intensely. This can mean that small troughs (like a ditch) are created, and when the ice finally melts, these troughs are filled with water, creating a ribbon lake.

    Glacial Erosion Landforms Lake Windermere with fields and trees StudySmarter Fig. 4 - Lake Windermere ribbon lake, the Lake District

    When the glacier meets rock that is harder to erode, it can actually move over it and abrade the rock below. This can create other kinds of landforms; Roches moutonnées and Crag and Tails.

    Roches moutonnée

    Cool name for a landform, right? Roches moutonnées are big chunks of rock on the landscape, with one side that is quite smooth, eroded by abrasion. The other side is much more rough, eroded by plucking. It is formed when ice moves over the rock that is more difficult to erode; with the direction of ice flow, the side of the rock hit first by the glacier is abraded (the stoss side). As it moves over the rock onto the other side, it plucks the rock away (on the lee side) as it moves further through the landscape, creating some pretty cool rock outcrops. They may also be covered in striations. Examples can be seen at Dulnain Bridge, Cairngorms National Park.

    Crag and Tail

    Although similar to a roche moutonnée, a crag and tail is a little different. This is where a glacier travels over a piece of resistant rock, with less resistant rock on either side. Erosional processes erode the softer rocks on the stoss side, leaving the chunk of resistant rock behind. This chunk of rock is the crag. On the lee side, the resistant rock (crag) actually protects the less resistant rocks here from erosion, leaving behind softer rocks, or the tail. Edinburgh is a great example of a Crag and Tail; the castle sits directly on top of the Crag, and The Royal Mile is the Tail!

    Glacial Erosion Landforms Edinburgh Castle StudySmarterFig. 3 - Edinburgh castle on top of a Crag and Tail

    Examples and case studies in geography are super important, so make sure you include examples of each of these landforms!

    Glacial Erosion - Key takeaways

    • Ice is an incredibly powerful material that has the ability to erode a landscape. Erosion is when (in this case) ice, wears the rock away, and brings the material with it.
    • The different processes of erosion include abrasion and plucking, and could also include weathering processes like freeze-thaw weathering.
    • Some of the different landforms created by glacial erosion include corries, arêtes, pyramidal peaks, U-shaped valleys, hanging valleys, truncated spurs, ribbon lakes, roches moutonnée and crag and tail, as well as striations.

    References

    1. Fig 1, an example of an arête in scotland (https://commons.wikimedia.org/wiki/File:Carn_M%C3%B2r_Dearg_Ar%C3%AAte_-_geograph.org.uk_-_3310206.jpg), by Russel Wills (https://www.geograph.org.uk/profile/23874), Licensed by CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0/)
    2. Fig 2, an example of a U-shaped valley (https://commons.wikimedia.org/wiki/File:National_Trust_Hut_-_geograph.org.uk_-_589050.jpg), by Ailith Stewart (https://www.geograph.org.uk/profile/635), Licensed by CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0/)
    3. Fig 3, Edinburgh castle as a crag and tail (https://commons.wikimedia.org/wiki/File:Castle_Rock_Edinburgh.jpg), by Scglossop1 (https://commons.wikimedia.org/w/index.php?title=User:Scglossop1&action=edit&redlink=1), Licensed by CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/)
    4. Fig 4, lake windermere ribbon lake (https://commons.wikimedia.org/wiki/File:Windermere_Lake_District_from_hill.JPG), by Abbasi1111 (https://commons.wikimedia.org/w/index.php?title=User:Abbasi1111&action=edit&redlink=1), Licensed by CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/)
    Frequently Asked Questions about Glacial Erosion

    What are glacial landforms?

    Glacial landforms are distinct marks on the landscape that have been formed by glacial erosion processes.

    What is glacial erosion?

    Glacial erosion is the process of ice scraping away material from a landscape/mountainside, bringing the eroded material with it.

    What are six landforms of glacial erosion?

    Some examples of landforms of glacial erosion include corries, arêtes, pyramidal peaks, hanging valleys, ribbon lakes, and truncated spurs. 

    What are the three main types of glacial erosion?

    The three main types of glacial erosion include abrasion, plucking, and freeze-thaw weathering (although freeze-thaw weathering is slightly different). 


    What is an example of glacial erosion? 

    An example of glacial erosion is abrasion, where rocks found inside a glacier scrape away at the rock face below and erode it. 

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