Glaciation

Glaciation

A glacier is an accumulation of ice, 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 valley glacier.

Causes of glaciation periods?In Antarctica, glaciers occur because the continent is located in a polar region. In the Rocky Mountains glaciers are caused by the coolness of the atmosphere at higher altitudes.The Milankovitch Theory (100,000 year cycles), suggests that Ice Ages were caused by variations in the Earth's orbit. This theory considers:

Eccentricity - The variance of the Earth's orbit from nearly circular to ellipticalThe Inclination of the Earth's axis - how tilted the Earth is with respect to the sunPrecession of the Equinoxes - Sometimes, the wobbling of the Earth as it moves around the sun can cause winter to occur at different times of the year.

Types of glaciersContinental Glaciers - Continental glaciers evolved during the Ice Ages. These glaciers are large sheets of ice, which cover vast areas and are unconfined by topography. For example, during the last Ice Age, ice covered all of Canada, and even parts of New York. Alpine (Valley) Glaciers - These glaciers form and flow within mountain valleys. They are especially common in high altitudes areas such as the Rocky Mountains.

How do glaciers move?One of the unique properties of glaciers is the way in which they move: their weight causes them to flow like a very slow moving river. When a glacier becomes thick enough (about 18 meters thick), it becomes so heavy that it begins to deform. The weight of the glacier, as well as gravity, causes the glaciers to flow very slowly. When flowing, the underside of the glacier is slowed by friction (due to contact with the ground beneath), while the surface of the glacier moves much faster. This causes a conveyor belt like motion down a slope.Glaciers can advance or retreat but the actual ice is always moving down slope.

Glaciation - mechanismsaccumulation - material added to the mass of the glacier or ice sheet (snow, rain).

accumulation zone - the area of the glacier or ice sheet where material is only added; no mass is lost. Usually this area is near the top of the glacier or ice sheet.

ablation - the process of removing material from the glacier or ice sheet (melting at the surface or the base, evaporation, calving). In Antarctica, most ablation occurs by calving ice off the ice sheet and ice shelf edges.

ablation zone - the area of the glacier or ice sheet where more mass is being lost than gained. In Antarctica, the ablation zone on most glaciers is small or at the edge of the ice.

Glaciation - mechanismshttp://www.glacier.rice.edu/land/

5_whatisaglacier.html

http://www.glacier.rice.edu/land/5_iceofallshapes.html#anchor609724

5

Glaciation - mechanisms

Calving!

Glaciation – Erosional landformsErosional subglacial features are those features created beneath the ice by the glacier removing rock material and transporting it away.They can be large scale, such as glacial valleys carved through the mountains, or small scale, such as the tiny striations engraved in pebbles!

Glaciation – Terms

Abrasion - mechanical grinding or wearing away of material.Striations - Grooves or scratches cut in the bedrock by the bottom of the glacierTill - Material picked up and carried by the glacier before being directly deposited from the ice. Erratics -Transported boulders of a different rock type than the bedrock.

Terms - AlpineCirques are the bowl shaped depressions found at the head of glacial valleys. For most alpine glaciers, cirques are the areas in the alpine valleys where snow first accumulated and was modified into glacial ice. Horns are pyramidal peaks that form when several cirques chisel a mountain from three or more sides. The most famous horn is the Matterhorn found in the Swiss Alps. Arêtes are the narrow serrated ridges found in glaciated alpine areas. Arêtes form when two opposing cirques back erode a mountain ridge.

Terms - ContinentalMoraines are ridges of sediment that are deposited perpendicular to glacier flow near the terminus of a glacier. Eskers are sinuous ridges of sand and gravel deposited in or under ice in a meltwater tunnel. Kames are hills of sediment that are commonly found near kettles. Kettles are depressions that were formed when a buried ice block melts

http://www.glacier.rice.edu/land/5_glaciallandforms.html#anchor8437

09

Glaciation – erosional landforms

Roches Moutonnees have a smooth side where the ice abraded and a jagged or rough side where the ice plucked the rock as it flowed over the obstacle. Roches moutonnees are excellent glacial flow directional indicators.

A moulin or glacier mill is a narrow, tubular chute, hole or crevasse through which water enters a glacier from the surface. They can be up to 10 meters wide and are typically found at a flat area of a glacier in a region of transverse crevasses

Glaciation – depositional landformsDepositional features are features created by the glacier depositing or releasing sediment. They vary in scale from thin ground cover to huge terminal moraines such as Cape Cod.Depositional features include landforms directly created by ice, but also include features that are created by glaciation indirectly, such as deltas and fans.

.

http://www.glacier.rice.edu/land/5_glaciallandforms.html#anchor8437

09

Glaciation – depositional landforms

Subglacial Moraines Moraines are accumulations of glacial material (till) that have surface expression. Based on that broad definition, there are several different types of moraines. Subglacial moraines, made of till, take on several shapes.

.

Glaciation – depositional landforms

Lateral Moraines and Medial Moraines Lateral moraines and medial moraines are not subglacial features, but they form in the glacial environment. They occur next to the glacier, and are in contact with the ice.

.

Glaciation – depositional landformsMoraines Moraines are accumulations of glacial material (usually till) shaped by the ice. Some moraines form under the ice, others form in front of the ice.

.

http://www.science.uottawa.ca/~users/clark/quat2333/Morin/

pres.html

Glaciation – depositional landformsMoraines con’t

Terminal or end moraines can be quite large. They are the result of all the material carried by the glacier to the glacier front, much as a bulldozer pushes and scrapes material into a pile. Terminal moraines mark the position of the ice where it was most extensive.Interlobate moraines are formed between two lobes of ice – such as the Oak Ridges Moraine in Southern Ontario

.

Alpine features

Continental Features

http://www.glacier.rice.edu/land/5_warmice.html

Glaciation – Where Are Glaciers Today?

In general, glaciers exist where ever the accumulation of frozen material is greater than the ablation (or loss) of frozen material. Most of us probably think of cold places, such as Greenland or Antarctica when we think of glaciers. But glaciers also exist in warmer places, such as New Zealand, Chile, and even pretty close to the equator in Africa!

.

http://www.glacier.rice.edu/land/5_iceofallshapes.html

Glaciation: What does the Future hold?

.