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Today, weβre going to learn about glaciers. Can someone tell me what a glacier is?
Isn't it just a big piece of ice?
That's correct, but glaciers are more than just ice; they're massive ice formations that move slowly over land. Glaciers can be classified as either continental glaciers, which cover large areas, or mountain glaciers, which flow down through valleys.
How fast can they move?
Good question! Glaciers can move as slowly as a few centimeters a day, depending on several factors. The movement is caused mainly by gravity.
What do they do to the land?
Glaciers are powerful agents of erosion. They reshape the landscape, forming unique features like U-shaped valleys and cirques.
So they can create new landforms?
Exactly! And we'll dive deeper into those landforms shortly.
To remember, think of glaciers as giant, slow-moving rivers of ice shaping the earth. This can be framed as 'Glaciers = Giant Ice Mowers'.
By the end of this topic, you should be able to explain how glaciers form, move, and their impact on the earth's surface.
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Now that we know about glaciers, let's talk about how they erode the landscape. One common feature is the cirque. Who can describe a cirque?
Isn't it a bowl-shaped depression?
That's right! Cirques are often found at the heads of glacial valleys and may form lakes called tarns once the glacier melts.
And what are horns?
Horns are sharp peaks formed when multiple glaciers erode a mountain from different sides. Think of them as natureβs way of making peaks pointy through erosion.
What about U-shaped valleys?
Great question! Glacial erosion creates U-shaped valleys, which differ from the V-shaped valleys formed by rivers. The broad, flat floor of the glacial valley is a key characteristic.
Finally, can anyone explain what moraines are?
Aren't they piles of rock and sediment at the edge of a glacier?
Exactly! Moraines can be terminal or lateral, indicating where the glacier deposited material. To remember all the landforms: 'Cirques are bowls, horns are peaks, U-shaped valleys are wide and deep, and moraines mark the fields and edges.'
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Weβve covered erosional forms, now letβs talk about the debris left behind by glaciers, known as glacial till. Who knows what till is?
Isn't it the debris dropped by glaciers?
Yes! Till consists of various sizes of rocks and sediment that glaciers leave behind as they melt. We can also discuss outwash, which occurs when meltwater streams carry and sort debris further from the glacier.
What are drumlins?
Drumlins are elongated mounds formed by the movement of glacial till. They are indicators of the direction of glacier movement. Think of them as the goosebumps on the ground left behind by glaciers.
And whatβs an esker?
Eskers are long ridges formed by sediment left by meltwater flowing beneath the glacier. They often appear as winding hills in a landscape and can provide insight into glacial movement.
To remember this, think: 'Till is dropped, outwash flows, drumlins shape from ice, and eskers wind below!'
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Now, letβs summarize what we've learned about glaciers. Can anyone list the main erosional forms?
Cirques, horns, U-shaped valleys, and moraines!
Exactly! And what about depositional landforms?
Till, outwash, drumlins, and eskers!
Superb! Glaciers really reshape our landscapes. Remember, their movements are slow, but the effects are profound. Whether through carving out valleys or depositing till, glaciers have a lasting impact on Earth's surface.
I really find it interesting how something so big can change the ground!
Thatβs the beauty of geology, and glaciers are a major player in shaping our planet. Always think 'Giant Ice Mowers of Earth' to recall their vital role. Well done today, everyone!
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Glaciers are large ice masses that move slowly over land, causing significant erosion and shaping various landforms. This section outlines the characteristics of glacial movement, the different types of glaciers, and the erosional and depositional landforms they create, such as cirques, horns, and moraines.
Glaciers are massive bodies of ice that move slowly across the land, defined by their formation and movement through gravity's force. There are different types of glaciers, including continental glaciers, which cover vast areas, and mountain glaciers, which flow down mountains in defined troughs. Their movement can range from a few centimeters to several meters per day, leading to noteworthy geological transformations.
As glaciers move, they erode landscapes through processes like abrasion and plucking, gradually reducing high peaks into lower forms, leaving behind a landscape marked with distinct features. The main erosional forms associated with glaciers include:
1. Cirques - Bowl-shaped depressions formed at the head of glacial valleys that may contain tarn lakes after glacial retreat.
2. Horns - Sharp peaks created when multiple glaciers erode a mountain from several sides.
3. U-shaped Valleys - Characteristic valleys shaped by the immense pressure and scraping action of moving ice, contrasting with the typically V-shaped valleys formed by rivers.
4. Moraines - Accumulations of debris deposited by glaciers, which can be lateral or terminal.
5. Fjords - Deep, U-shaped valleys that have been inundated by the sea, resulting from glacial erosion followed by rising sea levels.
Glaciers also contribute to sediment deposition, resulting in various landforms like drumlins and eskers as melted water transports and sorts glacial debris. Understanding glaciers is crucial for comprehending past and present climate impacts, highlighting their significant role in shaping Earthβs surface.
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Masses of ice moving as sheets over the land (continental glacier or piedmont glacier if a vast sheet of ice is spread over the plains at the foot of mountains) or as linear flows down the slopes of mountains in broad trough-like valleys (mountain and valley glaciers) are called glaciers.
Glaciers are large, slow-moving masses of ice formed from compacted snow. They can exist in various forms: continental glaciers cover vast areas of land, while mountain glaciers flow down valleys. The primary driver of glacier movement is gravity, which pulls the ice down slopes, allowing it to reshape the landscape beneath it.
Think of glaciers like gigantic rivers of ice. Just as you might see water flowing down a hill, glaciers glide slowly down mountain slopes, carving out valleys and changing the terrain over time.
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The movement of glaciers is slow unlike water flow. The movement could be a few centimetres to a few metres a day or even less or more. Glaciers move basically because of the force of gravity.
Unlike rivers that can rush down hillsides quickly, glaciers move at a much slower pace. This movement is mainly due to gravity pulling the heavy ice mass. Over time, this slow movement leads to significant erosion and shaping of the land beneath the glacier.
Imagine pushing a heavy box across a floor. You can only push it slowly, and if itβs heavy it may even scrape the floor beneath it. Similarly, glaciers drag along debris, reshaping the ground as they move.
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Fragments get dragged along the floors or sides of the valleys and cause great damage through abrasion and plucking. Glaciers can cause significant damage to even un-weathered rocks and can reduce high mountains into low hills and plains.
As glaciers move, they don't just flow smoothly; they also carry rocks and debris. This movement causes 'abrasion' where the glacier grinds against bedrock, and 'plucking' where chunks of rock are pulled away. Over thousands of years, this process can drastically wear down mountains, turning them into smoother, lower hills.
Think of glaciers as natureβs bulldozer. As they advance, they scrape and pick up rocks, much like a bulldozer pushes earth, reshaping the landscape to form valleys and plains.
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Cirques are the most common of landforms in glaciated mountains. The accumulated ice cuts these cirques while moving down the mountain tops. They are deep, long and wide troughs or basins with very steep concave to vertically dropping high walls at its head as well as sides.
Cirques form at the heads of glacial valleys where ice accumulates and slowly carves out a bowl-shaped depression. These depressions are steep and often hold water after the glacier melts, forming small lakes called tarns.
Visualize a big scoop of ice cream being carved out of a mountain. The scoop creates a bowl shape that can hold melted ice cream, resembling how glacial movement leaves cirques with lakes in sunny weather.
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Horns form through headward erosion of the cirque walls. If three or more radiating glaciers cut headward until their cirques meet, high, sharp pointed and steep sided peaks called horns form.
When multiple glaciers erode the same area, they can create sharp, steep peaks known as horns. This occurs because each glacier carves away the surrounding rock, meeting at a central peak, resulting in pointed mountain tops.
Imagine a cake being sliced from multiple directions. Each cut carves away a piece, ultimately leading to a taller central peak. Thatβs how horns are formed by the converging action of multiple glaciers.
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Glaciated valleys are trough-like and U-shaped with broad floors and relatively smooth, and steep sides. The valleys may contain littered debris or debris shaped as moraines with swampy appearance.
Glacial valleys differ from river valleys; they are U-shaped due to the expansive force of ice rather than the narrow V-shape typically created by water flow. Moraines, which are ridges of debris pushed by glaciers, often litter these valleys, giving them a distinct look.
Think of a U-shaped valley like a wide bowl. Just as a big spoon scoops out ice cream and forms the bowl shape, glaciers carve out these valleys, leaving rocky debris along the edges.
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They are long ridges of deposits of glacial till. Terminal moraines are long ridges of debris deposited at the end (toe) of the glaciers. Lateral moraines form along the sides parallel to the glacial valleys.
Moraines are piles of rocks and soil that have been pushed along by glaciers. Terminal moraines mark the furthest advance of a glacier, while lateral moraines form alongside it. These formations help us understand the historical movement of glaciers.
Consider moraines as the piles of leaves left behind after a child sweeps them into a heap. Just like the leaves, the moraine marks show where the glacier last scooped up and deposited material.
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Eskers are sinuous ridges formed by meltwater streams flowing beneath a glacier. Outwash plains are areas at the foot of glacial mountains covered with glacio-fluvial deposits.
As glaciers melt, streams can flow beneath them, depositing sorted sediment that forms eskers. Outwash plains are broader areas where meltwater spreads out, dropping finer materials, resulting in flat, fertile land.
Think of eskers like a hose that leaves behind a trail of sand when water flows through it. Similarly, when glaciers melt, the streams carry sediment and deposit it in long, winding ridges on the landscape.
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Key Concepts
Glaciers: Large masses of ice that shape the landscape through erosion and deposition.
Erosion: Glaciers erode rocks and soil, forming distinct features like cirques and U-shaped valleys.
Landforms: Glaciers create various landforms, including moraines, drumlins, and eskers.
Movement: Glacier movement is driven by gravity and occurs very slowly.
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The Matterhorn is a classic example of a horn formed by glacier erosion.
Cirque lakes, or tarns, often form in depressions left after glaciers melt.
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Glaciers glide, shaping land wide, carving deep valleys, their magic inside.
REM - Remember Erosion and Movement: Glaciers Move and Erase!
Once upon a time, giant ice rivers flowed through majestic mountains, slowly sculpting sharp peaks and wide valleys, leaving behind unique mounds and lakes filled with melted dreams.
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Review the Definitions for terms.
Term: Glacier
Definition:
A large mass of ice that moves slowly over land, formed from accumulated snow.
Term: Cirque
Definition:
A bowl-shaped depression at the head of a glacial valley formed by glacial erosion.
Term: Horn
Definition:
A sharp, pointed peak created by the erosion of three or more glaciers converging.
Term: Ushaped valley
Definition:
A valley with a U-shape profile that has been carved by glacial activity.
Term: Moraine
Definition:
A ridge of glacial debris deposited at the edges or terminus of a glacier.
Term: Drumlin
Definition:
An elongated hill formed by glacial till, indicating the direction of glacier movement.
Term: Esker
Definition:
A long, winding ridge formed by sediment deposited by meltwater flowing beneath a glacier.