Glaciation

Glaciation

"What causes ice sheets to expand and contract? Are the present ice sheets growing or shrinking? How will global warming impact the ice sheets? How do the ice sheets impact the global system? Glacial geologists study the present glacial environment to understand "ice ages" of the past. Come and explore the ever-changing nature of the glacial setting; the ice, the changes it creates in the landscape, and its response to changes in the environment!".

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.

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 - mechanisms

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

http://www.glacier.rice.edu/land/5_iceofallshapes.html#anchor6097245

Glaciation - mechanisms

http://sts.gsc.nrcan.gc.ca/page1/landf/ne/baffin/bylot/2crev.htm

Glaciation - landforms

Glaciers change the landscape in many ways. They erode the landscape, carving valleys, wearing away rock, and stripping soil from the ground. Glaciers also add to the landscape by depositing materials. Often the features left by glaciers, erosional or depositional, provide clues that tell the glacial geologist about the type and size of glacier!

Glaciation – erosional landforms

Erosional 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 – erosional landformsBecause subglacial features are formed under the ice, less is known about the processes that form them than is known about the features and processes in other glacial environments. It is rather difficult to go under an ice sheet to see what is happening!

For the most part, abrasion, plucking, and meltwater processes are the dominant activities at the ice base. Subglacial features provide a clue about the direction of ice flow, the nature of the base of the ice, and in some cases, the thickness of the ice.

Glaciation – erosional landforms

abrasion - mechanical grinding or wearing away of material.

http://www.glacier.rice.edu/land/5_glaciallandforms.html#anchor843709

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.

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.

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http://www.glacier.rice.edu/land/5_glaciallandforms.html#anchor843709

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.

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Glaciation – depositional landforms

EskersEskers are long linear depositional features that represent water flow in channels under the glacier (or within or even on top of the glacier). Meltwater in the glacier can form a network of tunnels that eventually reach the glacier front.

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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.

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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.

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

Glaciation – depositional landformsMoraines 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

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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!

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

Glaciation

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