Introduction

Glaciers have played a significant role in shaping the surface in many places around the world. Some of the most spectacular and, in some cases, the most boring landscapes are created by glaciers. Large continental glaciers have scoured the surface flat, leaving behind broad ridges and  pitted plains. In mountainous regions, alpine glaciers sculpt enormous amphitheaters from the sides of mountains and erode deep broad valleys. Here we'll look at how the two basic types of glaciers, continental and alpine, form and impact the topography of the earth.

Glaciers and Glaciation

Definition - natural accumulation of land ice showing evidence of movement.

Causes of Glaciation 

• Winter accumulation of snow exceeds summer loss

Types of Glaciers

• Alpine 
  • Range in size from a patch of ice to several thousands of square kilometers.
  • Found in all latitudes including the tropics
• Piedmont (a gentle slope leading from the base of mountains to a region of flat land.)
  • formed from merger of several alpine glaciers.
  • Lower slopes of mountains; several thousand to tens of thousands of square kilometers in area.
  • Lower slopes of the Himalayas & Andes

• Continental

  • Largest glacier; Pleistocene glaciers covered 5,00,000 km²

  • Greenland & Antarctica

Anatomy of Glaciers

Glacier Mass Balance Mass balance- difference between accumulation and ablation Accumulation Snow - density = 50 - 300 kg/m3 Firn - density = 600 - 700 kg/m3 Glacial Ice - density = 850 kg/m3 Ablation Melting  Sublimation Calving

Click image to enlarge

Movement of Glaciers Internal deformation Basal slipping Velocity greatest near top, slowest at bottom. Crevasse formation in upper fracture zone.

Landscape Modification

Erosional Processes

• Plucking (quarrying)

• Abrasion

• Crushing

Erosional Forms

• Chatter marks

• Striations

• Grooves

• Polished Bedrock

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Grooved bedrock, Quebec,  Canada

Photo Credit: Geological Survey of Canada

Grooved bedrock, Quebec Courtesy USGS DDS21 Click image to enlarge

Chatter marks Click image to enlarge

Striations Courtesy USGS DDS21 Click image to enlarge

Depositional Forms

• Glacial Drift

  • Till

  • Stratified Drift (Outwash)

• Erratic

Glacial Landforms

Continental Landforms

• Moraines

  • End Moraine

  • Ground Moraine

  • Interlobate Moraine

  • Recessional Moraine

• Esker
• Drumlin
• Kettle
• Kame
• Outwash Plain

Click on image to enlarge	Click on image to enlarge
Kettle Lake in glacial moraine Manitoba, Canada Photo credit: USGS Digital Data Series DDS-21	Glacial Till in moraine Rocky Mountain National Park, Colorado Photo credit: USGS Digital Data Series DDS-21

 

Alpine Landforms Moraine End Recessional Lateral Medial Cirque Arête Horn U - Shaped Valley Hanging Valley Staircase lakes
	Upper Yosemite Falls issues from a hanging valley   Photo Courtesy NOAA NGDC

Can you ...

• Describe the various causes of glaciation?

• Explain how a glacier erodes the earth's surface?

• Compare and contrast the different kinds of moraines?

• Describe how glaciers modify mountain valleys?