Erosion by Glaciers

Index

Types of GlaciersFeatures

DepositionFormation of Long Island

Types of Glaciers

•Glaciers that form on Large areas of the Continents are called Continental Ice Sheets

•World Map of Ice Sheets

•Glaciers that form in the valleys of mountains in high elevations are called Alpine Glaciers.

•Alpine Glacier

Continental Ice Sheets

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Alpine Glacier

What is a Glacier?A glacier is an accumulation of ice, air,

water, and rock debris or sediment. It is a large enough quantity of ice to flow

with gravity due to its own mass. Glaciers flow very slowly, from tens of meters to thousands of meters per year.The ice can be as large as a continent,

such as the ice sheet covering Antarctica. Or it can fill a small valley

between two mountains; a alpine (valley) glacier.

How does a Glacier Weather and Erode?

• Glaciers can weather rocks by bedrock crushing, chemical hydrolysis, and abrasion.– Abrasion Produces glacial striations

• Rocks and Sediment can be carried on top of, within or under a moving glacier.

• Glacial erosion produces specific features including, U shaped valleys, fjords, arêtes and horns.

• Glacial Depositional features include, till, moraines, erratics, kettle lakes and drumlins.

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Striations

Glacial Striations

• glacial striations Glacial striations are scratches and grooves on rock surfaces resulting from the gouging action of debris trapped in a moving ice sheet. The striations are oriented in the same direction as the movement of the ice.

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Glacial Erosion Features

The Matterhorn in Switzerland

Glacial Deposition• Glacial Till

– sediment deposited in contact with a glacier. It contains material that was picked up and carried by the ice. Often the pebbles in the till are poorly sorted, striated, and have broken edges. Till may be very hard, compacted by the weight of the overlying ice.

• Moraines– Sediment left by a moving glacier. Terminal and Lateral.

• Erratics– Large boulders that seem “out of place”

• Kettle Lakes– Kettle lakes form when a piece of glacier ice breaks off and becomes buried by glacial

till or moraine deposits. Over time the ice melts, leaving a small depression in the land, filled with water. Kettle lakes are usually very small, and are more like ponds than lakes.

• Drumlins– Tear shaped mounds of till, deposited by a receding glacier

Glacial Till

Moraines

Erratics

Glacial Lakes

Gifts of GlaciersGreat Lakes of North America

Finger Lakes of New York State

The Great Lakes

New York’s Finger Lakes

How the Great Lakes Formed

• Thousands of years ago, the melting mile-thick glaciers of the Wisconsin Ice Age left the North American continent a magnificent gift: five fantastic freshwater seas collectively known today as the Great Lakes -- Lake Superior, Lake Huron, Lake Michigan,  Lake Erie and Lake Ontario.

• The Great Lakes today hold an estimated six quadrillion gallons of water -- a fifth, or 20 percent, of all the drinkable water on the surface of Earth.

• If all the water in the Great Lakes were spread evenly over the continental U.S., the 48 states would be flooded under more than nine feet of water!

• Almost all of the Great Lakes' waters are a legacy of the glacier age with less than one percent renewed annually by precipitation and run off.

Drumlins• Tear shaped mounds of sediment left by a

receding glacier.

• Many found in New York State. Just look at a topographic map of Central New York.

Drumlins

Formation of Long Island

• Long Island formed from 2 Terminal Moraines. The Harbor hill Moraine and the Ronkonkoma Moraine.

• Approximately 20,000 years ago, glacial advances and retreats helped construct the hills and plains of Long Island. Acting like a giant bulldozer, it pushed sediment toward the South dumping its load to form a moraine that runs through central Long Island and extends to the south fork. This is the Ronkonkoma moraine. Another advance (from either the same glacier or another) created a moraine on the north shore known as the Harbor Hill moraine. The sediment in these moraines is typical glacial till, composed of unsorted material. Meltwaters running over the moraines deposited finer sediment called outwash. The outwash created the plains of Long Island.

Glaciers

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