Erosion by GlaciersErosion by Glaciers

A A glacierglacier is is Any large mass of ice that moves slowly over land

Think of it as a moving river of ice and snow

This is a glacier. Actually, it’s

several glaciers coming

together to form a larger one.

The glaciers are hundreds offeet thick. They have enormousmass. They flow downhill dueto the FORCE OF GRAVITY.

Glaciers form in areas where:Glaciers form in areas where:

The temperature is close The temperature is close to or below freezing most to or below freezing most of the year.of the year.

More snow falls than melts More snow falls than melts • Snow continues to fall on top of snow that is Snow continues to fall on top of snow that is

already on the ground, creating a layer of ice at already on the ground, creating a layer of ice at the bottom.the bottom.

What are 2 types of What are 2 types of glaciers?glaciers?

Valley GlaciersValley Glaciers Continental GlaciersContinental Glaciers

Continental & Valley GlaciersContinental & Valley Glaciers

SimilaritiesSimilarities Large masses of iceLarge masses of ice Move slowly on landMove slowly on land

Shape the landShape the land

Valley GlaciersValley GlaciersDef’nDef’n: : A long narrow glacier that

forms when snow and ice builds up in a mountain valley

Where are they located today?Where are they located today? Held in by sides of mountains.

Where were they located in the past?Where were they located in the past? U-shaped valleys U-shaped valleys show where show where

Valley glaciers once slid down Valley glaciers once slid down slowly slowly from a mountain.from a mountain.

Continental GlaciersContinental Glaciers

Def’nDef’n: : A glacier that covers much of a continent

Where are these located today?Where are these located today? Cover 10% of Earth Greenland & Antarctica

Where were they located in the past?Where were they located in the past? Ice Ages Ice Ages – when large parts of Earth – when large parts of Earth

were covered with Continental glacierswere covered with Continental glaciers

How fast do glaciers move?How fast do glaciers move?

From a few cm to 3000 cm per dayFrom a few cm to 3000 cm per day

Ice AgesIce Ages

An Ice Age is a period of very cold An Ice Age is a period of very cold temperatures.temperatures.• This causes glaciers to grow and spread.This causes glaciers to grow and spread.

The last Ice Age on Earth ended about The last Ice Age on Earth ended about 8,000 to 15,000 years ago.8,000 to 15,000 years ago.

During the last Ice Age, the sheet of During the last Ice Age, the sheet of ice around the North Pole expanded ice around the North Pole expanded to eventually cover most of North to eventually cover most of North America. America.

Cool Fact!Cool Fact!

Antarctica has the largest continental Antarctica has the largest continental ice sheet in the world: 1 and a half ice sheet in the world: 1 and a half times the size of the U.S. and in times the size of the U.S. and in some places 4,000 meters deep! some places 4,000 meters deep!

Cool Fact!Cool Fact!

If Greenland and Antarctica ice If Greenland and Antarctica ice sheets were to melt, the sea level sheets were to melt, the sea level would rise to 60 meters! would rise to 60 meters!

Glaciers are an endangered species. This is the Muir glacier in Glacier Bay, Alaska photographed in 2007.

The Muir Glacier is retreating rapidly. Ice is melting fasterthan new ice can replace it. The arrows show where the glacier was just a few years ago. As it melts it exposesrock that appears lighter because it hasn’t had time toweather.

These views show how the Muir Glacier has changed in just over half a century. In that time it has retreated over 20 km and it continues to get smaller every year.

People may debate the causes of global warming but the evidence is clear. The Earth IS warming.

How are glaciers different from How are glaciers different from icebergs?icebergs?

An An IcebergIceberg a large piece of a glacier a large piece of a glacier that has broken off and floated away that has broken off and floated away after a glacier reached the ocean.after a glacier reached the ocean.

Large amount of sediment may be Large amount of sediment may be frozen in an icebergfrozen in an iceberg

As it melts, the sediments sink to the As it melts, the sediments sink to the bottom.bottom.

Did you know?!?Did you know?!?

Only a small part of the iceberg is Only a small part of the iceberg is visible from above the water’s visible from above the water’s surfacesurface

Approximately 90% is below the Approximately 90% is below the water.water.

How do glaciers How do glaciers shape the land?shape the land?

Glaciers move due to the Glaciers move due to the force force of gravityof gravity..

AbrasionAbrasion Gravel and pieces of Gravel and pieces of rock are frozen into the ice rock are frozen into the ice at the bottom and sides of at the bottom and sides of

a glacier.a glacier. As a glacier moves, small As a glacier moves, small

pieces of bedrock are pieces of bedrock are scraped away.scraped away.

PluckingPlucking

The process by which a The process by which a glacier picks up rocks as it glacier picks up rocks as it

flows across the land. flows across the land.

U-Shaped ValleysU-Shaped Valleys

As a glacier scrapes away the floor As a glacier scrapes away the floor and sides of a valley, it becomes and sides of a valley, it becomes U-U-shaped.shaped.

Sometimes small side glaciers flow Sometimes small side glaciers flow into a main glacier into a main glacier When the side When the side glaciers melt, they leave small glaciers melt, they leave small glacier valleys, called glacier valleys, called hanging hanging valleys.valleys.

Which of these was formed by a Which of these was formed by a glacier? Which by running water?glacier? Which by running water?

TillTill DepositsDeposits of sediments of sediments

left behind as a glacier left behind as a glacier melts (clay, silt, sand, melts (clay, silt, sand,

gravel, boulders)gravel, boulders)

ErraticsErratics

A A boulder boulder left behind by a retreating left behind by a retreating glacier.glacier.

Did you know?!?Did you know?!?

New York City has many erratics in New York City has many erratics in Central Park!Central Park!

Brainpop on Glaciers and Ice AgesBrainpop on Glaciers and Ice Ages

http://www.brainpop.com/science/earthsystem/glaciers/