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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.
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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.
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.
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.
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.
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.
