Chapter 8 Erosional
Forces
Section 8-2 Glaciers
Note Guide
How Glaciers Move and Form
► Snow
remains on the ground year-round in
some areas of the world.
► As snow piles up, the weight increases and
it compresses the lower layers into ice.
► The pressure makes the ice plastic like, so
the mass begins to flow and move away
from its source.
► A large mass of ice and snow moving on
land under its own weight is a glacier.
An Advancing Glacier!
A glacier that has retreated!
Ice Eroding Rock
► Glaciers
are agents of Erosion.
► As glaciers move along the surface of the
Earth, they pick up eroded material and
deposit it somewhere else.
► When glacial ice melts, water flows into the
cracks of rocks. When the water freezes, it
expands and fractures the rock.
► The pieces of rock are lifted out by the ice.
This process is called plucking.
Ice Eroding Rock
►
►
►
Plucking results in boulders, gravel, and sand being added
to the bottom of glaciers.
Plucked rock fragments and sand at the bottom of a glacier
scrape and scour the soil and bedrock on Earth’s surface
and erode the ground.
 Deep, long, parallel scars called grooves are left behind
by rock fragments.
 Shallower marks on the bedrock are called striations
Both of these indicate the direction the glacier moved.
Plucking!
Striations
Ice Depositing Sediment
► When
glaciers begin to melt, they deposit
sediment on land.
► When a glacier melts and shrinks back, it is
said to retreat.
► As it retreats, it leaves a jumble of
boulders, sand, silt and clay behind.
► This is called glacial till.
Ice Depositing Sediment
► Till
is also deposited at the end of a glacier
when it is not moving.
► Rocks and soil are moved to the end of the
glacier and piles up in a big ridge.
► This ridge is called a moraine.
 Moraines are also deposited along the sides of a
glacier.
Moraine
Till
Outwash and Till
Ice Depositing Sediment
► In
a melting glacier, meltwater forms a
stream within the ice.
► This river carries sand and gravel and
deposits them within its channel.
► When the glacier melts, a winding ridge of
sand and gravel is left behind.
► This is called an esker.
Esker!
2 Types of Glaciers
► Continental
glaciers cover 10% of the
Earth, mostly near Antarctica and
Greenland.
► The continental glaciers are huge masses
of Ice and snow, and are thicker than some
Mountain ranges.
 In the past, continental glaciers covered as
much as 28 % of Earth. The periods of
widespread glaciations are known as Ice ages.
2 Types of Glaciers
► Valley glaciers occur today in high mountains
where the average temperature is low enough to
prevent snow from melting in the summer
 Evidence that valley glaciers existed in the
mountains includes striations or evidence of
plucking from the top of a mountain where the
glacier was in contact with solid rock.
 Valley glaciers erode curved, bowl- shaped
basins, called cirques into the sides of
mountains.
2 Types of Glaciers
 If two valley glaciers side by side erode a
mountain, then a long ridge called an Arête
forms between them.
 If valley glaciers erode a mountain from several
directions, a horn might form.
2 Types of Glaciers
►
►
►
To tell the difference between valleys that have been
eroded by glaciers or those that have been eroded by
streams:
Valleys that have been eroded by glaciers are U -shaped.
 Valleys that have been eroded by streams are V shaped.
Glaciers are important because they change the Earth’s
surface and they have left behind sediments that are
important resources.
Valley Glacier
Valley Glacier Erosion
Glacier Coverage!