Continental Glaciers Change Earth S Topography

Continental Glaciers Change Earth’s Topography

Introduction

Glaciers are thick masses of ice that change Earth's surface. One type of glacier,a continental glacier, or ice sheet, is an enormous mass of ice that flows in all directions from one or more centers. Today, continental glaciers cover about 10 percent of Earth's landscape, where the climate is extremely cold. Thousands of years ago, however, these glaciers were more extensive than they are today. At one time, these thick sheets of ice covered all of Canada, portions of Alaska, and much of the northern United States. The impact that these ice sheets had on the landscape is still obvious today.

Landforms produced by continental ice sheets, especially those that covered portions of the United States, are mostly depositional in origin. Recall that there are two types of glacial deposits. Stratified drift is sediment that is sorted and deposited by glacial meltwater. Till is unsorted sediment deposited directly by a glacier. Moraines are ridges of till deposited as a glacier melts and recedes. Ground moraines are gently rolling plains of rocks and other glacial debris. Ground moraines can fill low spots and result in poorly drained swamplands. End moraines are deposits that form along the end of a melting glacier. An outwash plain is a ramp-like accumulation of sediment downstream from an end moraine. Kettles are glacial features that form when blocks of stagnant ice become buried and eventually melt. Drumlins are streamlined hills that are composed of till.

In this investigation, you will use a topographic map to examine some of the features produced by continental glaciation. Recall that a topographic map is a map that shows a bird's-eye, or top, view of an area. Contour lines on a topographic map connect points of equal elevation. The difference in elevation between adjacent contour lines is the contour interval. Closely spaced contour lines indicate a steep slope, while contour lines that are farther apart indicate a gentle slope. A scale shows how horizontal distances on the map are related to actual distances on Earth's surface.

Problem

How do continental glaciers change Earth's topography?

Pre-Lab Discussion

Read the entire investigation. Then work with a partner to answer the following questions.

1. Measuring. What is the total length/ in miles, of the glacial feature labeled A?

The map scale is 1 inch equals 1 mile. The glacial feature labeled A is approximately 8.5 miles long.

2. Calculating Approximately how long, in miles, is Blue Spring Lake? Show your calculations.

The map scale is 1 inch equals 1 mile. The length of the lake on the map is 13/16 of an inch.

5280 ft/mi x 13/16 mi = 4209 ft

4290 ft/5280 ft = 0.8 mi

3. Interpreting Diagrams/Photographs. How does the topography ii the southeast corner of the map compare with the topography in he northwest part of the map?

The topography in the southeast corner of the map has a higher elevation, and it is more irregular than the land in the northwest.

4. Interpreting Diagrams/Photographs. What features on the map indicate that portions of the area are poorly drained? Where are these features located?

Marshes and swamps in the central and northwest portions of the map indicate that the area is poorly drained.

5. Comparing and Contrasting. How are glacial drift and till alike? How are they different?

Glacial drift and till are sediment deposited by glaciers. Drift is sorted sediment deposited by meltwater. Till is unsorted debris that is deposited directly from the ice.

Materials(per pair of students)

metric rulercalculator (optional)

Procedure

1. Closely examine the Whitewater, Wisconsin, topographic map. If necessary, refer to amap symbol guide..

2. Use the topographic map and what you have learned about glaciers to answer theAnalysis and Conclusions questions.

Analysis and Conclusions

1. Interpreting Diagrams/Photographs The feature labeled A on the map is unsorted glacial debris. What is this structure, and how did it form?

The feature labeled A is a moraine that formed as the leading edge of the glacier melted and receded.

2. Interpreting Diagrams/Photographs. What are the structuresonthe map labeled B? Find and label another example of this structure on the map.

The structures labeled B are drumlins. Another drumlin, which is much larger than those labeled, is located southwest of Zion Cemetery.

3. Inferring. Where on the map is the likely location of the outwash plain?

The southeast quarter of the map is the outwash plain.

4. Interpreting Diagrams/Photographs What are the structureson the map that are labeled C? How do these structures form?

The structures labeled C are kettles, or kettle lakes. They form when blocks of stagnant ice become buried and eventually melt.

5. Inferring Where on the map might you find ground moraine?

Ground moraine was deposited in the western and northeastern parts of the area shown.

6. Applying Concepts In which direction did the continental glacier that changed this part of Wisconsin move? Give two lines of evidence to support your answer.

The ice moved from north to south or slightly southeast. This direction of movement is supported by the orientation of the drumlins, whose steep sides face the direction from which the ice advanced and the position of the moraine labeled A.

Go Further

If necessary, review how to make a topographic profile, Rivers Shape the Land. Then use the Whitewater topographic map to make a northwest-southeast topographic profile from the Scuppernong River to the city of Little Prairie.

Earth Science Lab Manual, Prentice Hall, Upper Saddle River, NJ