Glacier Motion

In this lesson, students are introduced to glaciers, the largest reservoir of fresh water on the planet. Glaciers flow like extremely slow-moving rivers, reshaping the landscape by carving out lakes, valleys, and fjords. Students conduct an experiment to test how the angle of a slope affects the speed a polymer glacier moves, and then model how glaciers weather and erode Earth’s materials as they move over the land.

• Glaciers are flowing masses of ice and snow that form on mountaintops and near the North and South poles, and they contribute to the cycling of Earth’s materials.
• Even though they are made of layers of solid ice, glaciers flow like powerful, extremely slow-moving rivers. Glaciers are reservoirs because they store water for a period of time.
• Glaciers are part of the hydrosphere because they are made up of solid water, and because of this, they are part of the global water cycle—the circulation of water through the hydrosphere from Earth’s surface to the atmosphere and back.
• Glaciers change the land as they move over it, contributing to the cycling of Earth’s materials.

• What is the difference between alpine glaciers and continental glaciers?
• How is the formation of glaciers similar to the formation of sedimentary rock?
• What causes glaciers to flow?
• Why does water cycle between states of matter?
• How would you describe the role of gravity in the water cycle?
• How are the effects of gravity on water in the water cycle similar to the effects of gravity on glaciers?
• How does the landscape change as glaciers move over it?
• Why do alpine glaciers flow down the mountain?

Misconception: The Ice Age happened in the past.

Fact: We are currently in a warmer period within an ice age, and Earth has experienced multiple ice ages since it first formed.

Misconception: Glaciers don’t move.

Fact: The force of gravity constantly works on glaciers, causing them to move. Some glaciers move very slowly, but they are still moving.

Glacial till : the eroded sediment that is deposited as glaciers retreat and expand

Glacier : a flowing mass of ice and snow that forms on mountaintops and near the North and South poles

Gravity : the attractive force between all matter

Water cycle : the circulation of water through the hydrosphere from Earth’s surface to the atmosphere and back

Weathering : the breakdown of rock into smaller pieces from exposure to wind, water, gravity, changes in temperature, and/or biological forces

Studying Earth’s Ice

Every month during the summer, a ship carrying scientists and support staff arrives at a small research station on an island in Antarctica. This station is called Palmer Station. It is one of three stations that the United States has on Antarctica, which is Earth’s most southern continent. About 98 percent of the continent is covered by ice. It is the coldest, driest continent in the world.

Living in Antarctica is unlike life anywhere else. The station is so remote that all supplies arrive by ship, usually about once a month. Most of the scientists at the station study marine biology. They focus on the wildlife that live in the region, including penguins and elephant seals. The station also acts as a base for scientists who collect different kinds of data about how the ice is changing as Earth’s temperature warms.

People who live in Antarctica have to adjust to the cold and also the extreme days and nights. The sun shines for nearly 24 hours a day during the summer. And then, for a couple of weeks during the winter, there is no direct sunlight. The sun rises a few degrees above the horizon, but it stays behind a glacier, so the station remains in its shadow. A glacier is a flowing mass of ice and snow that forms on mountaintops and near the North and South poles.

The entire continent of Antarctica is made up of glaciers. Glaciers form when snow accumulates in the same area over many years. Each year, new layers of snow bury and compress the previous layers, similar to how layers of sediment compress over time to form sedimentary rock. Over many years, the snow becomes more compacted and denser until it turns into ice. Glaciers cover 15 million square kilometers of Earth’s land surface and hold ice that can be hundreds or hundreds of thousands of years old.

How Glaciers Move

Even though they are made of layers of solid ice, glaciers flow like powerful rivers. The weight of a glacier is what causes it to move. Weight is the gravitational force exerted on an object by a planet or moon. Gravity is the attractive force between all matter. Gravity is a result of an object’s mass. The more massive an object is, the more its gravity will pull on other objects. Non- scientists often think that an object’s weight is the same as its mass. The two are related because an object’s weight depends on its mass. However, weight also depends on the force of gravity. Here on Earth, weight is calculated by multiplying the object’s mass by the force of Earth’s gravity.

Glaciers are so massive that Earth’s gravity pulls down on the upper layers of ice, causing them to slowly move downward. This is possible because ice is softer than rock. The force of the glacier’s own weight deforms the ice so that it flows down mountains or spreads out across plains or the ocean.

At the same time as glaciers flow, they can also either expand or retreat. A glacier expands when winter snowfalls are greater than summer snowmelt. It retreats when winter snowfalls are less than summer snowmelt.

One category of rock is formed as a result of the tremendous heat and pressure of Earth’s interior. Metamorphic rocks are rocks formed in chemical reactions where one type of rock is changed by pressure or heat into a new type of rock with different properties. For example, the heat of Earth’s magma and the pressure of the rock layers above turn soft limestone into hard marble.

Most glaciers expand or retreat very slowly. It can take many years for there to be a significant change. However, sometimes glaciers retreat very quickly. For example, Muir Glacier in Alaska has retreated 12 kilometers (7 miles) in just 40 years. Ocean water now fills the valley where the glacier used to be.

For the main activity of this lesson, students create polymer glaciers to analyze how gravity drives the flow of alpine glaciers downhill. Students also use ice cube glaciers to model the cycling of Earth’s materials in an investigation. Students use the data they gather from the experiment and investigation to figure out how gravity causes glaciers to move over the land, and how this movement causes weathering and erosion, which change Earth’s surface over time by contributing to the cycling of Earth materials.