Cirque/ Corrie, Glacial Trough, Hanging Valley, Arete, Horn, D. Fjord – Glacier Erosional Landforms

Sculpted by Ice: A Journey Through Glacier Erosional Landforms

Glaciers, vast rivers of ice, are powerful agents of change, carving and shaping the Earth’s surface over millennia. Their relentless movement and immense weight leave behind a distinctive landscape, a testament to their erosive power. This article delves into the fascinating world of glacier erosional landforms, exploring their formation, characteristics, and the unique features that distinguish them.

Cirque/ Corrie: The Cradle of a Glacier

A cirque, also known as a corrie, is a bowl-shaped depression nestled high in the mountains, often serving as the birthplace of a glacier. Its formation is a testament to the relentless power of ice.

Formation:

1. Snow Accumulation: Snow accumulates in a sheltered area on a mountainside, typically a north-facing slope in the Northern Hemisphere.
2. Snow Compaction and Recrystallization: Over time, the weight of the accumulating snow compresses the lower layers, transforming them into firn, a denser, granular form of ice.
3. Glacier Formation: As more snow accumulates, the firn transforms into glacial ice, a solid, crystalline mass.
4. Erosion and Excavation: The glacier, driven by gravity, begins to flow, eroding the surrounding bedrock through a combination of abrasion (grinding by rock fragments embedded in the ice) and plucking (lifting and removal of rock fragments by the ice).
5. Cirque Formation: The erosive action of the glacier creates a steep, bowl-shaped depression, with a characteristically steep back wall and a lip at the lower end.

Characteristics:

• Bowl-shaped depression: The most defining feature of a cirque is its bowl-like shape, with a steep back wall and a lip at the lower end.
• Tarn: A cirque often contains a small, deep lake called a tarn, formed by the melting of the glacier and the subsequent accumulation of water in the depression.
• Rock Steps: The back wall of a cirque may exhibit rock steps, formed by the differential erosion of alternating hard and soft rock layers.
• Glacial Polish and Striations: The bedrock within a cirque often displays glacial polish, a smooth, polished surface created by the abrasive action of the glacier. Striations, parallel scratches etched into the rock by embedded rock fragments, are also common.

Examples:

• Yosemite National Park, California: The iconic Half Dome and El Capitan are remnants of ancient cirques.
• Snowdonia National Park, Wales: The Cwm Idwal cirque, with its tarn and surrounding peaks, is a classic example of this landform.

Glacial Trough: A Valley Shaped by Ice

A glacial trough, also known as a U-shaped valley, is a valley carved by the erosive power of a glacier. It stands in stark contrast to the V-shaped valleys formed by rivers.

Formation:

1. Pre-existing Valley: Glaciers typically form in pre-existing river valleys, often with a V-shaped profile.
2. Glacial Erosion: As the glacier flows through the valley, it widens and deepens it through abrasion and plucking.
3. U-shaped Profile: The erosive action of the glacier transforms the V-shaped valley into a characteristic U-shaped profile, with steep, almost vertical sides and a flat, wide floor.

Characteristics:

• U-shaped Profile: The most defining feature of a glacial trough is its U-shaped profile, with steep, almost vertical sides and a flat, wide floor.
• Truncated Spurs: The sides of a glacial trough often exhibit truncated spurs, triangular-shaped features formed by the erosion of the valley sides.
• Hanging Valleys: Smaller tributary valleys that join the main glacial trough often end abruptly at a higher elevation, forming hanging valleys.
• Glacial Polish and Striations: The bedrock within a glacial trough often displays glacial polish and striations, similar to those found in cirques.

Examples:

• Yosemite National Park, California: Yosemite Valley is a classic example of a glacial trough, with its towering granite cliffs and U-shaped profile.
• Fiordland National Park, New Zealand: The Milford Sound, a dramatic fjord carved by glaciers, is another striking example of a glacial trough.

Hanging Valley: A Tributary Left High and Dry

A hanging valley is a smaller valley that joins a larger glacial trough at a higher elevation, creating a dramatic waterfall or cascade.

Formation:

1. Tributary Glacier: A smaller glacier flows down a tributary valley, eroding it into a smaller U-shaped valley.
2. Main Glacier Erosion: The main glacier, flowing through the larger valley, erodes more effectively than the tributary glacier, deepening the main valley.
3. Hanging Valley Formation: As the main glacier erodes deeper, the tributary valley is left hanging at a higher elevation, creating a dramatic drop between the two valleys.

Characteristics:

• Abrupt Drop: The most defining feature of a hanging valley is the abrupt drop between the tributary valley and the main glacial trough.
• Waterfall or Cascade: The drop often creates a waterfall or cascade, as water from the tributary valley flows down to the main valley.
• U-shaped Profile: The tributary valley itself typically exhibits a U-shaped profile, characteristic of glacial erosion.

Examples:

• Yosemite National Park, California: Yosemite Valley features numerous hanging valleys, including the iconic Bridalveil Fall and Yosemite Falls.
• Fiordland National Park, New Zealand: The Milford Sound is renowned for its numerous hanging valleys, which contribute to its dramatic beauty.

Arete: A Knife-Edge Ridge

An arete is a sharp, narrow ridge formed by the erosion of two opposing glaciers. It is a testament to the precise and powerful erosive forces of ice.

Formation:

1. Two Opposing Glaciers: Two glaciers flow down adjacent valleys, eroding the intervening ridge.
2. Erosion and Convergence: The glaciers erode the ridge from both sides, creating a sharp, narrow crest.
3. Arete Formation: As the glaciers retreat, the eroded ridge remains, forming a knife-edge feature known as an arete.

Characteristics:

• Sharp, Narrow Ridge: The most defining feature of an arete is its sharp, narrow crest, often resembling a knife blade.
• Steep Sides: The sides of an arete are typically steep and often vertical.
• Jagged Appearance: The erosion process often leaves the arete with a jagged, irregular appearance.

Examples:

• Yosemite National Park, California: The granite peaks of El Capitan and Half Dome are separated by a series of arêtes.
• Snowdonia National Park, Wales: The jagged peaks of the Snowdon Massif are formed by a network of arêtes.

Horn: A Pyramid-Shaped Peak

A horn is a pyramid-shaped peak formed by the intersection of three or more arêtes. It is a striking example of the intricate interplay of glacial erosion.

Formation:

1. Multiple Glaciers: Three or more glaciers flow down adjacent valleys, eroding the surrounding peaks.
2. Arete Formation: The glaciers erode the peaks from multiple sides, creating arêtes.
3. Horn Formation: As the glaciers retreat, the arêtes intersect, forming a pyramid-shaped peak known as a horn.

Characteristics:

• Pyramid-shaped Peak: The most defining feature of a horn is its pyramid-shaped form, with a pointed summit.
• Steep Sides: The sides of a horn are typically steep and often vertical.
• Sharp Edges: The edges of a horn are formed by the intersecting arêtes, creating sharp, jagged ridges.

Examples:

• Matterhorn, Switzerland: The iconic Matterhorn, with its distinctive pyramid shape, is a classic example of a horn.
• Mount Blanc, France: The highest peak in the Alps, Mount Blanc, is also a horn, formed by the intersection of multiple arêtes.

Fjord: A Drowned Glacial Trough

A fjord is a long, narrow inlet of the sea, formed by the submergence of a glacial trough. It is a dramatic testament to the interplay of glacial erosion and sea-level rise.

Formation:

1. Glacial Trough Formation: A glacier carves a deep, U-shaped valley, creating a glacial trough.
2. Sea-Level Rise: As the glaciers retreat, sea levels rise, flooding the glacial trough.
3. Fjord Formation: The flooded glacial trough becomes a fjord, a long, narrow inlet of the sea, with steep, often vertical sides.

Characteristics:

• Long, Narrow Inlet: The most defining feature of a fjord is its long, narrow shape, often extending far inland.
• Steep Sides: The sides of a fjord are typically steep and often vertical, reflecting the U-shaped profile of the glacial trough.
• Deep Water: Fjords are often very deep, reflecting the depth of the original glacial trough.
• Threshold: Fjords often have a shallow threshold at their entrance, formed by the deposition of sediment by the retreating glacier.

Examples:

• Sognefjord, Norway: The Sognefjord, the longest and deepest fjord in Norway, is a classic example of this landform.
• Milford Sound, New Zealand: The Milford Sound, a dramatic fjord carved by glaciers, is another striking example of a fjord.

Table 1: Summary of Glacier Erosional Landforms

Conclusion: A Legacy of Ice

The glacier erosional landforms discussed in this article are a testament to the immense power of ice. They are not merely geological features but also breathtaking landscapes that inspire awe and wonder. From the towering peaks of the Alps to the dramatic fjords of Norway, these landforms offer a glimpse into the Earth’s dynamic history and the enduring legacy of glacial erosion. As we continue to explore and understand these remarkable features, we gain a deeper appreciation for the forces that have shaped our planet and the intricate beauty that results from their relentless work.

Frequently Asked Questions about Glacier Erosional Landforms

Here are some frequently asked questions about the six glacier erosional landforms discussed in the article:

Cirque/ Corrie:

Q: What is the difference between a cirque and a corrie?

A: “Cirque” and “corrie” are essentially the same landform. “Cirque” is the French term, while “corrie” is the Scottish Gaelic term. Both refer to the bowl-shaped depression formed by glacial erosion.

Q: Can a cirque form without a glacier?

A: While glaciers are the primary agents of cirque formation, other erosive forces like frost wedging and nivation (erosion by snow and ice) can contribute to the development of cirque-like features. However, a true cirque is typically associated with glacial activity.

Q: What is the significance of a tarn in a cirque?

A: The presence of a tarn, a small, deep lake within a cirque, indicates that the cirque was once occupied by a glacier. The tarn is formed by the melting of the glacier and the subsequent accumulation of water in the depression.

Glacial Trough:

Q: How can I tell if a valley is a glacial trough or a river valley?

A: A glacial trough has a characteristic U-shaped profile with steep, almost vertical sides and a flat, wide floor, while a river valley typically has a V-shaped profile. Additionally, glacial troughs often exhibit features like truncated spurs and hanging valleys, which are not found in river valleys.

Q: What is the relationship between a glacial trough and a fjord?

A: A fjord is essentially a drowned glacial trough. When sea levels rise after the retreat of a glacier, the glacial trough is flooded, forming a long, narrow inlet of the sea known as a fjord.

Hanging Valley:

Q: Why are hanging valleys called “hanging”?

A: Hanging valleys are called “hanging” because they are positioned at a higher elevation than the main glacial trough they join. This creates a dramatic drop between the two valleys, often resulting in a waterfall or cascade.

Q: Can hanging valleys form without glaciers?

A: While glaciers are the primary agents of hanging valley formation, other erosive forces like rivers and landslides can contribute to the development of similar features. However, a true hanging valley is typically associated with glacial activity.

Arete:

Q: How are arêtes different from ridges?

A: While both arêtes and ridges are narrow, elevated features, arêtes are specifically formed by the erosive action of two opposing glaciers. This results in a sharper, more knife-like crest than a typical ridge.

Q: Can arêtes form in areas without glaciers?

A: While glaciers are the primary agents of arete formation, other erosive forces like wind and frost wedging can contribute to the development of similar features. However, a true arete is typically associated with glacial activity.

Horn:

Q: What is the difference between a horn and a peak?

A: While both horns and peaks are pointed summits, horns are specifically formed by the intersection of three or more arêtes. This results in a more pyramid-shaped form than a typical peak.

Q: Can horns form without glaciers?

A: While glaciers are the primary agents of horn formation, other erosive forces like wind and frost wedging can contribute to the development of similar features. However, a true horn is typically associated with glacial activity.

Fjord:

Q: What is the difference between a fjord and a bay?

A: While both fjords and bays are inlets of the sea, fjords are specifically formed by the submergence of a glacial trough. This results in a longer, narrower shape with steeper sides and deeper water than a typical bay.

Q: Can fjords form without glaciers?

A: Fjords are exclusively formed by the submergence of glacial troughs. They are a direct result of glacial erosion and subsequent sea-level rise.

These FAQs provide a starting point for understanding the unique characteristics and formation processes of these fascinating glacier erosional landforms.

Here are some multiple-choice questions about glacier erosional landforms:

1. Which of the following landforms is a bowl-shaped depression formed by glacial erosion?

a) Arete
b) Horn
c) Cirque/ Corrie
d) Fjord

2. A glacial trough is characterized by its:

a) V-shaped profile
b) Steep, almost vertical sides
c) Gentle, sloping sides
d) Circular shape

3. Which of the following features is NOT typically found in a glacial trough?

a) Truncated spurs
b) Hanging valleys
c) Tarn
d) Glacial polish

4. A hanging valley is formed when:

a) A glacier erodes a tributary valley more effectively than the main valley
b) A river erodes a tributary valley more effectively than the main valley
c) Two opposing glaciers erode a ridge
d) A glacier erodes a pre-existing valley

5. Which of the following landforms is a sharp, narrow ridge formed by the erosion of two opposing glaciers?

a) Arete
b) Horn
c) Cirque/ Corrie
d) Fjord

6. A horn is formed by the intersection of:

a) Two arêtes
b) Three or more arêtes
c) Two glacial troughs
d) A cirque and a glacial trough

7. Which of the following landforms is a drowned glacial trough?

a) Arete
b) Horn
c) Cirque/ Corrie
d) Fjord

Answers:

1. c) Cirque/ Corrie
2. b) Steep, almost vertical sides
3. c) Tarn
4. a) A glacier erodes a tributary valley more effectively than the main valley
5. a) Arete
6. b) Three or more arêtes
7. d) Fjord