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6.7 - EROSIONAL LANDFORMS

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Cirques

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Teacher
Teacher

Today, we will discuss cirques, one of the primary erosional landforms created by glaciers. Can anyone describe what a cirque is?

Student 1
Student 1

Is it a type of valley?

Teacher
Teacher

Good observation! Cirques are indeed valleys, specifically deep, trough-like basins found at the heads of glacial valleys. They are formed as glaciers move down mountain slopes, eroding the landscape. Let's remember this with the acronym 'CIRCLES' \u2014 C for 'Cirque', I for 'Ice', R for 'Removal of rock', and E for 'Erosion'.

Student 2
Student 2

Do cirques always have lakes?

Teacher
Teacher

Great question! Often, after glaciers melt, these cirques can hold lakes known as tarns. So, remember, cirques can contain lakes after the glacial period.

Horns and Serrated Ridges

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Teacher
Teacher

Now let's talk about horns and serrated ridges. Who can tell me how these form?

Student 3
Student 3

Are they created when glaciers meet?

Teacher
Teacher

Exactly! Horns form when three or more glaciers erode towards each other. This creates sharp, pointed peaks. The ridges that separate these cirques are called ar\u00eates, and they have a zig-zag outline thanks to the erosion. Can anyone think of famous examples of horns?

Student 4
Student 4

Isn't the Matterhorn a horn?

Teacher
Teacher

That\u2019s correct! The Matterhorn is one of the most iconic horns, illustrating these processes perfectly. Let's recap: Cirques erode down into basins, horns arise from multiple glaciers eroding towards a point, and serrated ridges form in between.

Glacial Valleys and Fjords

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Teacher
Teacher

Lastly, let\u2019s explore glacial valleys. Who can describe how a glacial valley differs from a river valley?

Student 1
Student 1

Is a glacial valley U-shaped?

Teacher
Teacher

Yes! Glacial valleys are typically U-shaped with broad floors, unlike the V-shaped cross-sections of river valleys. This is due to the deeper and more powerful erosion caused by glaciers. Can anyone suggest what might happen when some glacial valleys become submerged?

Student 2
Student 2

They form fjords?

Teacher
Teacher

Exactly! Fjords are deep glacial troughs filled with seawater. They often create dramatic coastal landscapes. So, in summary, we learned about cirques, horns, ar\u00eates, and the unique characteristics of glacial valleys and fjords.

Introduction & Overview

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Quick Overview

Erosional landforms, primarily shaped by glacial activity, include features such as cirques, horns, and glacial troughs, each representing distinct processes of erosion in mountainous regions.

Standard

This section explores the various erosional landforms created by glacial processes, focusing on cirques, horns, serrated ridges, and U-shaped glacial valleys. It highlights the characteristics and formation mechanisms of these features, including cirque lakes and hanging valleys, as well as comparing glacial valleys to river valleys.

Detailed

Erosional Landforms\n\nErosional landforms are primarily carved by glaciers, leading to a variety of distinct features. Cirques are characterized as deep, trough-like basins often found at the heads of glacial valleys, formed by the ice that cuts through as it moves down the mountains, often containing post-glacial lakes known as tarn lakes. \n\nHorns and serrated ridges form through headward erosion of cirque walls. When three or more glaciers erode their cirques towards the center, sharp peaks called horns arise. Meanwhile, the narrowing divides between these cirques transform into jagged ridges, termed ar\u00eates. \n\nThe section also discusses glacial valleys, which are U-shaped with broad floors and steep sides, often littered with debris known as moraines. Some valleys may possess lakes gouged out of their floors or created by debris, while hanging valleys can also be present at higher elevations. Deeper glacial troughs along shorelines known as fjords form when these valleys are submerged.\n\nIn summary, the key features of erosional landforms highlight the intricate relationship between glacial movements and the landscape, allowing for a better understanding of geological formations.

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Audio Book

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Cirques

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Cirques are the most common of landforms in glaciated mountains. The cirques quite often are found at the heads of glacial valleys. 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. A lake of water can be seen quite often within the cirques after the glacier disappears. Such lakes are called cirque or tarn lakes. There can be two or more cirques one leading into another down below in a stepped sequence.

Detailed Explanation

Cirques are unique landforms created by the eroding action of glaciers found at mountainous areas. They typically appear at the beginnings of glacial valleys. As glaciers move down the slopes, they carve out these cirques, resulting in deep basins with steep walls. After the glacier melts, these basins often fill with water, forming lakes known as tarns or cirque lakes. Additionally, it\u2019s common to find multiple cirques in a stepped manner, where one cirque leads into another below it.

Examples & Analogies

Think of cirques like large scoops taken out of a mountain, similar to how a spoon scoops out ice cream from a tub. Once the ice cream (glacier) melts, the scoop (cirque) can hold melted ice cream (water) left behind, creating a small lake.

Horns and Serrated Ridges

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Horns form through head ward 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. The divides between cirque side walls or head walls get narrow because of progressive erosion and turn into serrated or saw-toothed ridges sometimes referred to as ar\u00eates with very sharp crest and a zig-zag outline. The highest peak in the Alps, Matterhorn and the highest peak in the Himalayas, Everest are in fact horns formed through headward erosion of radiating cirques.

Detailed Explanation

When glaciers erode the cirque walls, they can create pointed peaks known as horns. These occur when multiple glaciers meet at a specific point, eroding the terrain from different angles. The areas between the cirque walls become narrower due to this ongoing erosion, resulting in sharp-edged ridges known as ar\u00eates. Famous mountains, such as the Matterhorn in the Alps and Mount Everest in the Himalayas, are examples of these horns, showcasing the dramatic effects of glacial erosion.

Examples & Analogies

Imagine a cake being cut from multiple sides \u2013 the spots where the knife meets are like the horns of mountains, and the points where the cuts get narrower resemble the serrated ridges. Just as the cake has peaks where each cut comes together, mountains have these peaks shaped by glaciers.

Glacial Valleys/Troughs

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Glaciated valleys are trough-like and Ushaped with broad floors and relatively smooth, and steep sides. The valleys may contain littered debris or debris shaped as moraines with swampy appearance. There may be lakes gouged out of rocky floor or formed by debris within the valleys. There can be hanging valleys at an elevation on one or both sides of the main glacial valley. The faces of divides or spurs of such hanging valleys opening into main glacial valleys are quite often truncated to give them an appearance like triangular facets. Very deep glacial troughs filled with sea water and making up shorelines (in high latitudes) are called fjords/fiords.

Detailed Explanation

Glacial valleys are distinctively shaped by the carving action of glaciers, creating a U-shape rather than a V-shape seen in river valleys. They often feature broad, smooth floors and steep sides. Inside these valleys, you might find debris left behind by the glacier, known as moraines. Sometimes, lakes emerge within these troughs, either from glacial melt or accumulated material. Some glacial valleys may also have higher side valleys known as hanging valleys, which have been cut off and appear as facets along the main valley. In high-latitude regions, deep glacial troughs can become fjords, partially filled with seawater.

Examples & Analogies

Imagine a U-shaped mold that a glacier has pushed through soft dough. Once the glacier melts, the dough leaves behind a wide valley. The hanging valleys can be thought of as shelves sticking out from this U-shaped mold, showcasing how the glacier has shaped the landscape.

Differences Between Glacial Valleys and River Valleys

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What are the basic differences between glacial valleys and river valleys?

Detailed Explanation

Glacial valleys and river valleys differ mainly in their shape and formation process. Glacial valleys tend to be U-shaped due to the broad, heavy ice of glaciers moving through them, while river valleys usually have a V-shape created by flowing water. The steep and smooth sides of glacial valleys result from the powerful scraping effect of glaciers, while river valleys often have more irregular features due to erosion from water flow.

Examples & Analogies

Consider a U-shaped channel carved by a bulldozer versus a wavy creek. The bulldozer represents the glacier, creating broad, smooth walls, while the creek cuts a narrower path through the land, resembling a river valley.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Cirques are formed by glacier erosion and often contain lakes.

  • Horns form when multiple glaciers erode towards each other, creating pointed peaks.

  • Ar\u00eates are sharp ridges formed from headward erosion of cirque walls.

  • Glacial valleys are U-shaped, contrasting with V-shaped river valleys.

  • Fjords are submerged glacial valleys filled with seawater.

Examples & Real-Life Applications

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Examples

  • The Matterhorn in the Alps exemplifies a horn formed by glacial activity.

  • Fjords like those found in Norway are developed from U-shaped glacial valleys that are submerged.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎵 Rhymes Time

  • Cirques carve deep, with ice they creep; horns rise high, like mountains in the sky.

📖 Fascinating Stories

  • Once upon a time, glaciers roamed the mountains, carving deep bowls called cirques. As they moved, they met one another, creating sharp peaks \u2014 the horns. The valleys they left behind were U-shaped, but where the sea kissed them, there lay fjords, deep and beautiful.

🧠 Other Memory Gems

  • Remember C.H.A.R. \u2014 Cirque, Horn, Ar\u00eate for glacial features you see. A cirque is a bowl, a horn is a peak, an ar\u00eate is a jagged ridge, unique!

🎯 Super Acronyms

C.I.R.C.L.E \u2014 Cirque, Ice, Rock removal, Carving, Lake existence.

Flash Cards

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Glossary of Terms

Review the Definitions for terms.

  • Term: Cirque

    Definition:

    A deep, trough-like basin at the head of a glacial valley formed by glacial erosion, often containing a lake.

  • Term: Horn

    Definition:

    A sharp pointed peak that forms when glaciers erode towards each other.

  • Term: Ar\u00eate

    Definition:

    A serrated ridge formed by the headward erosion of cirque walls.

  • Term: UShaped Valley

    Definition:

    A glacial valley with a U-like cross-section, characterized by broad floors and steep sides.

  • Term: Fjord

    Definition:

    A deep, glacial valley that has been partially submerged by seawater.