Glacier Motion

In this unit, students analyze the phenomena that have shaped Earth’s surface, analyzing how gravitational energy moves glaciers, which have sculpted the land over time. This page showcases elements of the first lesson which focuses on glacier motion.

Science Background for Teachers:

Science background gives teachers more in-depth information on the phenomena students explore in this unit. Below is an excerpt from the science background on glacier motion.

Types of Glaciers

There are two types of glaciers: continental glaciers and alpine glaciers. Continental glaciers, also known as ice sheets, are masses of ice and snow that permanently cover an extensive area of land in Earth’s polar regions. For example, the Antarctica ice sheet has existed for at least 40 million years, and it is 4.8 kilometers (3 miles) thick in places. Scientists estimate that if it were to entirely melt, it would cause sea levels around the world to rise 60 meters (200 feet).

In addition to continental glaciers, there are also alpine glaciers, which form on mountains and flow down valleys. They form at high altitudes where the air is thin and temperatures are low. The ice moves downward by riding over a layer of meltwater at the glacier’s base.

At the top of the mountain, alpine glaciers have a kind of potential energy called gravitational energy, which is the energy stored in an object as a result of its vertical position or height. The taller the mountain, the more gravitational potential energy the glacier has. This is a cause-and-effect relationship. The height of the mountain causes the amount of energy stored in the glacier to change. Once the glacier starts moving, that gravitational potential energy transforms into kinetic energy. As the glacier moves down the mountain, gravitational potential energy is constantly transforming into kinetic energy.

Even though they are made of solid ice, glaciers flow like powerful rivers, pulled downward by their own weight. Weight is the gravitational force exerted on an object by a planet or moon. Gravity is the attractive force between all matter. Gravity is what keeps you on Earth and pulls all objects back toward Earth’s surface.

A Changing Landscape

Weathered Earth materials become frozen to the bottom of the glacier and get carried along with it. Those pieces of sediment get dragged over the land, weathering the land in the same way that sandpaper wears down and smoothes objects. They can also be deposited far away from their original location. The eroded sediment that is deposited as glaciers retreat and expand is called glacial till. Moraines are narrow ridges that are left behind from glacial till gathered on a glacier’s surface or sides.

As glaciers erode Earth materials, they carve out the land beneath them. A result of this is that the movement of a glacier can significantly change the landscape. For example, the movement of glaciers can create glaciated valleys. These valleys are usually very deep with vertical walls. As glaciers recede, they can also create fjords, which are long and narrow valleys. They are often U-shaped, with steep sides and a rounded bottom.

When seawater fills the land, it creates fjords. Lakes can also form when pieces of glacial ice break off and melt. These lakes are usually shallow and filled with sediment from the glacial ice.

Part of the Global Water Cycle

One reason that scientists study the Antarctic glaciers is that the glaciers are an important part of the global water cycle. The water cycle is the circulation of water through the hydrosphere from Earth’s surface to the atmosphere and back. Water is continually changing from a solid to a liquid or gas and back to a solid depending on the amount of thermal energy (heat) present from the sun.

Glaciers currently cover 10 percent of the planet and hold almost 70 percent of the world’s fresh water. The water held in glaciers is in “storage.” Some of the water in Antarctica has been there for thousands of years. Because of this, glaciers are considered reservoirs. Reservoirs are places where water is stored for a period of time, including glaciers, oceans, and the atmosphere.

Water in glaciers is solid ice. Remember that solids have the least amount of thermal energy of all of the states of matter. Water molecules in solid ice are closely packed together and vibrate in place.

Water in the atmosphere is called water vapor, which is water’s gas state. Much of the water in the atmosphere cycles between liquid water and water vapor through two processes: precipitation and evaporation. Evaporation is the process of liquid water changing into water vapor. Water evaporates when enough thermal energy is present. Like all liquids, the atoms and molecules that make up liquid water are less tightly packed than they are in a solid. They are in constant contact with one another, but they have enough energy to slide past one another.

When thermal energy is added to liquid water, the atoms and molecules begin to speed up. When enough thermal energy is added, the atoms or molecules will move so quickly that the water expands, becoming water vapor.

Supports Grade 7

Science Lesson: Discovering 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.

Science Big Ideas

  • 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.

Sample Unit CTA-2
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Science Essential Questions

  • 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?

Common Science Misconceptions

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.  

Science Vocabulary

Erosion : the transport of sediment by wind, water, or gravity

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

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

Lexile(R) Certified Non-Fiction Science Reading (Excerpt)

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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.

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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.

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.

 

Hands-on Science Activity

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.

Science Assessments

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Science Standards

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Download the Alignment to NGSS

Standards citation: NGSS Lead States. 2013. Next Generation Science Standards: For States, By States. Washington, DC: The National Academies Press. Neither WestEd nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.