Geology 200

Study Guide

Unit 9:
Glaciers and Glaciation

Overview

In previous units we looked at the sculpturing effects of running water at the Earth’s surface as well as the effects of mass wasting. We identified running water and mass wasting as the most effective geomorphic agents on the surface of the Earth. Many consider glaciers to be the third most effective sculpturing agent acting at the Earth’s surface. Glaciation is responsible for a wide range of landforms, which include fjords that characterize some coastal margins; mountain peaks such as those in the Rockies and the rolling hills of midwest USA and southern Canada; and basins such as the Great Lakes of North America.

Unit 9 introduces glaciers, their distribution, and how they form; and then discusses how glaciers move, how they erode, how they carve into the Earth, and how they transport eroded material. Glacial deposition and the resultant landforms are discussed next, after which the unit concludes with a look at past glaciations and how geological information can be used to reconstruct such events.

Objectives

After completing this unit, you should be able to

  1. explain the differences between an alpine glaciation and a continental glaciation.
  2. describe the differences between a valley glacier, an ice sheet, and an ice cap.
  3. outline the concept of a glacial budget, and describe how it can be used to explain whether a glacier advances or recedes.
  4. describe how valley glaciers and continental ice sheets move by basal sliding and plastic flow.
  5. describe how crevasses develop on glaciers.
  6. outline the range of erosional landforms associated with alpine glaciations, including glacial valleys, cirques, horns, and arêtes.
  7. describe erosional landscapes associated with continental glaciations.
  8. outline features associated with glacially deposited materials, including till and erratic.
  9. explain the characteristics of till that occurs as moraine, and describe the different types of moraine, including lateral moraine, medial moraine, end moraine, and ground moraine.
  10. describe the features of till that occur as drumlins.
  11. explain characteristics of outwash deposits, including eskers, kames, and kettles.
  12. explain how glacial outwash sediments can give rise to loess deposits.
  13. explain how direct evidence of past glaciations can be used to reconstruct past environments.
  14. describe how indirect evidence of past glaciations such as glacial lakes, pluvial lakes, and sea level changes can be used to reconstruct past environments.

Section 1: Introduction: Glacier Types, Formation, and Growth

Section 1 begins with a basic introduction to glaciers and the significant role they play in landscape development. Next, we will examine the distribution of glaciers by looking at environmental conditions that promote their development. After outlining the types of glaciers, the section concludes by exploring the factors that influence the formation and growth of glaciers.

Reading Assignment

Plummer, C. C., Carlson, D. H., & Hammersley, L. Physical Geology (15th ed.).

  • Introduction to Chapter 12: Glaciers and Glaciation, iIncluding "What is a Glacier?" (pp. 287-288).
  • “Glaciers—Where They Are, How They Form and Move” (up to “Movement of Valley Glaciers”) (pp. 289-292).

Study Questions

  1. What is a glacier? In what settings do glaciers form? What is the difference between an alpine glacier and a continental glacier?
  2. What is the world’s largest resource of freshwater?
  3. Explain the differences between a valley glacier, an ice sheet, and an ice cap.
  4. How does powder snow differ from corn snow?
  5. How does firn form? What conditions lead to the formation of glacier ice?
  6. Explain what calving means with reference to glaciers.
  7. What differentiates a receding glacier from an advancing one? Under what conditions can a glacier attain a balanced budget?
  8. Where does the zone of accumulation and the zone of ablation occur on a glacier, and how are these zones related to the equilibrium line?

PDF icon Answer Key

Section 2: Movement of Glaciers

In this section, we look at how glaciers move. First we explore the movement of valley glaciers, and then the movement of ice sheets. The driving force behind both is gravity.

Reading Assignment

Plummer, C. C., Carlson, D. H., & Hammersley, L. Physical Geology (15th ed.).

  • “Movement of Valley Glaciers” (pp. 292-295).
  • “Movement of Ice Sheets” (pp. 295-296).

Study Questions

  1. What force drives the movement of valley glaciers?
  2. How does ice movement vary within a valley glacier?
  3. How does ice grain movement in the rigid zone differ from movement in the plastic zone?
  4. Explain how crevasses form on valley glaciers.
  5. What are ice streams in an ice sheet? How would one determine the boundaries of an ice stream?

PDF icon Answer Key

Section 3: Glacial Erosion

Section 3 examines the erosional effects of glaciers. We will look at the landscapes associated with alpine glaciation first, and then discuss landforms that develop in continental glaciations.

Reading Assignment

Plummer, C. C., Carlson, D. H., & Hammersley, L. Physical Geology (15th ed.).

  • “Glacial Erosion” (pp. 296-304).

Study Questions

  1. What is rock flour, and how does it form?
  2. Explain how rocks that collect in the zone of accumulation are transported differently from rocks that accumulate in the zone of ablation.
  3. How does a glacially-carved valley differ from one that is carved by stream erosion?
  4. What are roches moutonnées?
  5. How does a cirque form?

PDF icon Answer Key

Section 4: Glacial Deposition

In this section we examine the landscapes that are produced by glacial deposition. Glaciers carry vast amounts of materials, ranging in size from fine dust particles to huge boulders. At some point, especially when the glaciers melt away or recede, these materials are deposited as sediments. In this section you will learn about the different types of sediments that glaciers deposit and the landforms they form.

Reading Assignment

Plummer, C. C., Carlson, D. H., & Hammersley, L. Physical Geology (15th ed.).

  • “Glacial Deposition” (pp. 304-309).

Study Questions

  1. What is glacial till?
  2. What are erratics?
  3. Describe the terms lateral moraine, medial moraine, and end moraine.
  4. What is the difference between end moraine and recessional moraine?
  5. What are drumlins?
  6. Explain how glacial outwash forms. What is an esker?
  7. What is a kettle?
  8. Explain how varves can be used to determine the duration of glaciations.

PDF icon Answer Key

Section 5: Past Glaciation

By now you are aware of the capacity of glaciers to carve the surface of the Earth and will appreciate that glaciations leave an indelible mark on the surface of the Earth. In this section, we explore how this knowledge can be used to reconstruct the extent and timing of past glaciations. You will also learn that glaciations have increased in frequency during the ice ages of the last 2.5 million years (although there have been other periods in the geologic past during which ice sheets were extensive), and examine speculations for this increase in ice age recurrence.

Reading Assignment

Plummer, C. C., Carlson, D. H., & Hammersley, L. Physical Geology (15th ed.).

  • “Past Glaciation” (pp. 309-316).

Study Questions

  1. What is believed to be the primary cause for glacial ages? Why is glaciation not found with uniform frequency throughout geological history?
  2. Describe briefly how glaciation contributed to the formation of the Great Lakes.
  3. Where was Lake Agassiz, and how did it form?
  4. What are pluvial lakes?
  5. Why did the sea level drop during glacial periods?
  6. What causes crustal rebound following glacial retreat?

PDF icon Answer Key

Unit 9 Self Test

You have now finished Unit 9, so please complete and submit the associated laboratory exercise and assignment. Instructions can be found in the Assignment Drop Boxes section of the course homepage.

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