World Geography Unit 1: Land and Water Forms Glaciers as Agents of Erosion

Glaciers

What Are Glaciers? Glacier: Large sheet of ice that flows like a river under the influence of gravity. Today 1/10 of Earth’s land surface is covered by ice years ago it was nearly 1/3 Thus ice has had a huge impact on the physical world we see today

Types of Glaciers The glaciers that we see today are of two different types. –Alpine Glaciers: Glaciers that form high in mountain valleys above the snowline. –Continental Glaciers: Large sheets of ice that cover portions of the continental land mass.

Differences Continental and Alpine Glaciers differ in two ways: –Location: Alpine glaciers are only found on mountains whereas continental glaciers are only found and the earth’s poles regardless of elevation –Size: Alpine glaciers are smaller compared to continental glaciers.

Similarities They both move and cause erosion Both types change the features of the landscape Both developed in the same way; bodies of water subjected to constantly cold temperatures below freezing for very long periods of time.

The Last Ice Age

Ice Cover Today

How Do Glaciers Grow? Glaciers can be seen as an open system –Input – Snow –Output – Ice, meltwater, and water vapor At its upper end the glacier is fed by snow this area is known as the accumulation zone If a Glacier receives more input than it loses in output the glacier grows. Accumulation Zone: where a glacier grows Ablation Zone: Where a glacier loses mass

How Does a Glacier Move? The movement of a glacier has much to do with the properties of the ice that makes up the glacier At different depths glacial ice has different properties, and behaves in different ways At the top it is solid, much like ice in a freezer, however deep within the glacier the ice is plastic, more like a frozen jelly This plastic ice distorts itself, and flows in response to the upper layers of ice, and the slope of the land

Glacial Mass and Balance

Depositional Glacier Terms Depositional Glacier Terms The following is a list of terms that are useful in talking about glaciers –Outwash plain –Terminal Moraine –Erratic –Drumlin –Esker

Outwash Plain Outwash plain: Glacial stream deposits of stratified drift or melt-water fed, braided and overloaded streams; occurs beyond a glaciers moraine deposits.

Terminal Moraine Terminal Moraine: Eroded debris that is dropped at a glacier’s farthest extent; forming a ridge like structure

Erratic Erratic: a piece of rock that deviates from the size and type of rock native to the area in which it rests. These rock are carried by glaciers and deposited when they melt.

Erratic A piece of rock that is left behind by a glacier, that is obviously not like the surrounding rocks. As glaciers move they pick up large chunks of rock, as they melt the rocks are left behind.

Drumlin Drumlin: A depositional landform related to glaciation that is composed of till (unstratifeid, unsorted eroded material) and is streamlined in the direction of continental ice movement; blunt end upstream and tapered end down stream with a rounded top.

Drumlin

Esker Esker: A curving, snakelike, narrow deposit of coarse gravel that forms along a melt-water stream channel developing in a tunnel beneath a glacier.

Esker

Evidence of Movement There are three things to look for when trying to determine the direction of movement of a glacier: –The gently sloped end of drumlins point in the direction of glacier movement –The terminal moraine marks the furthest edge of the glacier –The layers of silt in an outwash plain can indicate the direction of glacier movement. Fine particles would be at the leading edge while larger particles would have been closer to the glacier.

Erosional Landforms Alpine glaciers create spectacular, dramatic landforms that bring to mind the Canadian Rockies. Some of these features include; –Cirque –Arête –U-Shaped valley –Hanging valley –Terminal Moraine

Cirque Cirque: A scooped-out, amphitheater- shaped basin at the head of an alpine glacier valley.

Arête Arête: A sharp ridge that divides two cirque basin. Derived from “knife edge” in French, these form sawtooth and serrated ridges in glaciated mountains.

U-Shaped Valley U-Shaped Valley: Large deep valley created by the main glacier in a flow gouging down deep into the bedrock

Hanging Valley Hanging Valley: Like a tributary to a river a hanging valley consists of a smaller ice flow that runs into the main glacier. It gets its name because it does not carve as deep into the ground, resulting in a valley at a higher altitude

Terminal or End Moraine Terminal moraine: Eroded debris that is dropped at a glacier’s farthest extent

Lateral Moraine Lateral Moraine: Debris transported by a glacier that accumulates along the sides of the glacier and is deposited along the margins.

Fjords Fjord: A drowned glacial valley near the coastline Formation –A large glacier erodes troughs and valleys in mountains extending to the coast –Carving a large U shaped valley –When the Glacier melts seawater floods the valley