Glacial Ice Action

By Bourdeau, Virginia | Science Scope, October 2008 | Go to article overview

Glacial Ice Action


Bourdeau, Virginia, Science Scope


Glaciers are not just part of the geologic past; they are active today in the arctic regions of mountains and in the Arctic and Antarctic. Current news reports discuss the loss of glacial ice in the Antarctic and Greenland as examples of the effects of global warming. But what are glaciers and how do they work? An understanding of the process that causes ice to melt is important in understanding the causes of global glacial loss.

Glaciers form when more snow falls than is melted each year. Over time, the collecting snow packs down and turns to ice crystals. This is similar to what happens when you make a tightly packed snowball. A snowball is much denser than the original snow used to make it. If you have access to snow you can demonstrate this using two measuring cups. Fill one cup with a scoop of loose snow. Pack the second cup tightly with snow. Both cups will be "full." Ask students which cup contains more snow. How can we find out? Allow the snow to melt and compare the volume of water in the cups.

Continental glaciers are ice sheets that cover large land masses. During the Pleistocene epoch, from two million to 10,000 years ago, continental glaciers covered 30% of the Earth's surface. So much water was frozen into continental glaciers that the sea level was lowered along the continental coastlines. The Great Lakes are a result of the huge weight of continental glaciers. Basins that filled with meltwater were left behind as the glaciers receded. When continental glaciers reach the ocean they can form an ice shelf over the water. Large masses of ice can break away from the front of the ice shelf, creating icebergs.

Where I teach, there are mountain ranges that have been shaped by mountain glaciers. These glaciers are rivers of ice that begin at high-altitude snowfields and flow through mountain valleys. Deep U-shaped valleys, hanging valleys, and jagged ridges are landforms that tell of glacial activity.

A glacier can carry rocks and boulders with it as it moves forward. This "sandpaper" ice leaves characteristic marks on the land. Rocks that are too large for the glacier to move will have grooves cut in their surfaces by the weight and scouring action of the glacier. These are called abraded rocks.

Large rocks may be carried hundreds of miles from their source by glaciers. When they are deposited, they are called glacial erratics. Deposits of unsorted sediment left at the sides and front of a melting glacier are called moraines.

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In this activity, you will bring glaciers into the classroom, where student teams will use their inquiry skills to design simple investigations to test how glaciers change landforms. While this activity is somewhat messy, the active learning is worth it.

Materials

You will need access to a freezer with space for the glacier models. For a class of 30 students, prepare six sets of glacier models as described below.

* Aquarium gravel (25 lb. bag)

For each student:

* Safety goggles

For each student team:

* A plastic storage box, approximately 18 x 30.5 cm (7 x 12 in.)

* Four custard cups or paper cups cut down to approximately 5 cm

* Two pieces of lumber, 5 x 15 x 35.5 cm (2 x 6 x 14 in.) (large home improvement stores can cut lumber for customers)

* One ski-type glove or mitten

Preparing the glacier models

At least two days before conducting the activity, freeze three identical glacier models and one model of plain ice for each student team. For the plain ice model, fill one cup per student team with plain water and freeze. For each of the three glacier models, fill the cups two-thirds full with water and freeze (Figure 1). When the water in the cups is frozen, sprinkle the ice surface of the glacier models (three per team) with gravel (Figure 2).

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