What Are Glaciers? - Definition, Types & Processes

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  • 0:07 What Are Glaciers?
  • 0:46 How Glaciers Move
  • 2:30 Two Types of Glaciers
  • 4:10 Landforms Created by Glaciers
  • 4:59 Lesson Summary
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Lesson Transcript
Instructor: Elizabeth Friedl

Elizabeth, a Licensed Massage Therapist, has a Master's in Zoology from North Carolina State, one in GIS from Florida State University, and a Bachelor's in Biology from Eastern Michigan University. She has taught college level Physical Science and Biology.

Learn about the two major types of glaciers: continental and alpine glaciers. These glaciers shape the landscape around them and affect our everyday lives, even if the nearest glacier is thousands of miles away.

What Are Glaciers?

Most of the earth is covered with water, and most of that is salty and in the oceans. In fact, about 97% of Earth's water is ocean water. The remaining 3% is fresh water, and two thirds of that is frozen in glaciers. Glaciers are large masses of ice that can take many forms, from huge sheets to jagged blocks of slow-moving ice and rock. For billions of years, glaciers have carved the earth's surface and fed rivers and oceans with water. Their presence is still felt even millions of years after melting away to create valleys, lakes and even mountains.

How Glaciers Move

Glaciers are formed from the accumulation of ice and snow. But in order for this to become a glacier, it has to move under its own weight. An accumulation of ice isn't considered a glacier until it starts moving. Once it does start moving, though, it acts like a giant plow that scrapes and scours the earth. As glaciers move across the land, they loosen and pick up rocks along the way, dragging them across the earth's surface and creating striations, which are just large scratches that are formed in the direction of glacial movement.

A glacier may move in two ways. Internal flow is when the pressure and gravity on the ice in a glacier cause it to move downhill. This movement is like pushing a deck of cards from one side. As you push the deck of cards, the base of the deck moves very little, because it is in contact with the table, and there is more friction here. Conversely, the cards at the top of the deck move faster, because there's less friction. Basal sliding is when an entire glacier moves because its base is slightly melted. Instead of mostly internal movement, the bottom of the glacier slides downhill as well. This makes the glacier able to move much like an ice cube is able to glide across a table if it is pushed.

Even though glaciers are moving, trying to watch this movement would be like trying to watch grass grow. Most move only a few feet or inches each day, though some glaciers have been known to move as fast as 50 meters in a single day; this is about 160 feet, or about the equivalent in length of 16 minivans.

The Two Types of Glaciers

Continental glaciers are also known as ice sheets because they envelop everything in sight with a layer of - you guessed it - ice. These are the kind of massive, all-consuming glaciers that might bring to mind images of ice ages and polar bears, and they currently cover the earth's poles and very cold places, like Greenland. Because they are so massive, continental glaciers smooth the earth's surface as they move. The markings they leave behind are not very obvious, but since continental glaciers cover such large pieces of land, scientists can use the striations left behind to study how continents used to be linked together.

Alpine glaciers are created from the densely packed snow and ice found on top of mountains as well as in the valleys between them. Once alpine glaciers begin their downhill descent, they start their slow-moving havoc on the terrain around them.

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