Erosional Landforms by Glacial: Cirques, Aretes, Glacial Valleys

Introduction

Glaciers are big sheets of ice that slide slowly over the land. They can cover wide areas, like plains next to mountains, or flow down valleys between mountains. Glaciers move slowly because of gravity, which pulls them downhill. Sometimes they move just a little bit each day, while other times they can move more quickly. In this way, glaciers shape the land around them, creating unique and fascinating features called glacial landforms.

Understanding Glacial Erosion

• Glaciers: These are masses of ice that move over the land in various forms, covering approximately 10% of the Earth’s surface. 
  • Example: Continental glaciers cover vast plains at the foot of mountains, while Piedmont glaciers spread over plains. 
• Erosion Processes: A glacier erodes its valley by two processes: plucking and abrasion. 
  • Plucking: Glacier freezes the joints and beds of the underlying rock, tears out individual blocks, and drags them away.
  • Abrasion: Glacier scratches, scrapes, polishes, and scours the valley floor with the help of debris frozen into it.
• Snowline: It marks the elevation where the average temperature remains below freezing during the warmest month.

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Overview of Glacial Erosional Landforms

• These landforms are formed through abrasion, plucking, and polishing; Coarse debris at the base aids in bedrock and side wall erosion.
• Cirque: They are amphitheatre-like, steep-walled depressions at the head of glacial valleys. 
  • They are deep, long and wide troughs or basins with very steep concave to vertically dropping high walls at thier head as well as sides
  • Typically located at the heads of glacial valleys. 
  • It is also known as a corrie.
  • Cirques often contain lakes known as cirque or tarn lakes. 
  • Cirques are formed by glacial erosion, primarily abrasion and plucking. 
  • Example: Chandra Taal, Himachal Pradesh.
• Aretes: When two corries cut back on opposite sides of a mountain, knife-edged ridges are formed, called aretes.
  • Where three or more cirques cut back together, their ultimate recession will form an angular horn or pyramidal peak.
• Bergschrund: At the head of a glacier, where it begins to leave the snowfield of a corrie, a deep vertical crack opens up called a bergschrund (in German) or rimaye (in French)
• Glacial Valleys/Troughs
  • Glaciated valleys are U-shaped valleys with broad floors and relatively smooth, steep sides. 
  • These valleys may contain debris moraines, and, sometimes, lakes.
• A Ribbon Lake/ Finger Lake/ Trough Lake: is a long and very deep, finger-shaped lake, usually found in a glacial trough
• Hanging Valley: After the ice has melted, a tributary valley hangs above the main valley so that its stream plunges down as a waterfall. 
  • After deglaciation, meltwater from hanging valleys often forms waterfalls when joining the main valley. 
  • Example: Har-Ki-Doon Valley, Uttarakhand
• Fjords or Fiords: In high latitudes, deep glacial troughs filled with seawater create fjords or fiords.
• Roche Moutonnee: This is a resistant residual rock hummock. 
• • The surface is striated by ice movement. 
  • Its upstream side is smoothed by abrasion, and its downstream side is roughened by plucking.
• Crag and Tail: A crag is an outcropping of hard rock with a high upward slope that keeps the ice from entirely wearing down the softer, leeward slope. 
• Horns (Pyramidal peak): Horns are pyramidal or triangular peaks created when three or more cirques intersect, leading to the steepening and sharpening of the peak.
• Nunataks: Isolated peaks or mounds surrounded by glacial ice; 
  • They resemble small islands within the ice mass and decrease in size over time due to glacial lateral erosion and frost action. 

Conclusion

Glacial erosional landforms are shaped by processes like abrasion, plucking, and polishing, with coarse debris aiding in bedrock and sidewall erosion. From the cirques to aretes, each feature bears witness to the power of ice. Glacial valleys, ribbon lakes, and fjords showcase the transformative impact of glaciers on Earth’s surface. As glaciers advance and retreat, they leave behind a legacy of rugged beauty, marked by crags, horns, and nunataks, etching their story into the fabric of the land.

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