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1

Continental glacier

As this glacier grows it collapses down and outward moving the sediment at its base.

- the rock fragment has been eroded (set in motion by the moving ice)

- as ice moves across the bed rock it has little affect. If there is friction the ice melts. This rock fragment, however will scrape against the bedrock

- as a result of this abrasion both the rock fragment and the bedrock are ground down and small pieces of rock are created.

- as a result of the two weathering processes -- frost action and abrasion -- sediment is created that has two distinct sizes - large and small.

- it also means that scratches or striations occur in bedrock and the large rock fragments have a number of flat surfaces.

- multiple flat surfaces occur as this rock is reowrked at the base of a glacier

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Weathering processes that occur in a glacier

Frost Action and Abrasion

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What happens when there are "bumps" in the bedrock beneath a glacier?

At A, on the up-ice side of this bedrock protrusion, the ice slows down as it encounters this obstacle.
With increased pressure and friction the ice melts.

The ice also bends and flows around the obstacles. n

4

What happens when there are "bumps" in the bedrock beneath a glacier?

- At A, on the up-ice side of this bedrock protrusion, the ice slows down as it encounters the obstacle.
With increased pressure and friction the ice melts.

-The ice also bends and flows around the obstacles. If there is any sediment at the base of the ice it will start to grind away, smooth and polish the bed rock.

- ar B the solid ice and meltwater have moved around the obstacle where there is less pressure. On this down-ice side meltwater refreezes

- as a result the bedrock is physically weathered by frost action

- the end result is a change in the shape of the bedrock obstacle into an asymmetrical hill with smooth, more gentle sloping up-ice and a jagged down-ice side.

- ROCHE MOUTONNEE

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ROCHE MOUTONEE

An erosion bedrock glacial feature.

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Glacial Weathering

1. Frost Action
2. Abrasion

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Abrasion

The grinding of one rock against another.

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Glacial weathering FROST ACTION end result

Large Pieces

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Glacial weathering ABRASION end result

Small Pieces

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Glacial Erosion

Sediment is set in motion by moving ice, and to a lesser degree melt water.

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Glacial Transport

(3)

1. Supra-glacial (on the ice)
2. Englacial (in the ice)
3. Subglacial (beneath the ice)

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how does sediment get into the ice?

- buried by snow
- ice and sediment at the base was deflected upwards as the glacier moved

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How/When does Glacial Deposition occur? Where?

This occurs most often when the ice melts. It may also occur when sediment beneath the moving ice becomes detached and is left behind by the ice.

This can happen in:
- Hollows in the bedrock
- Behind obstructions
- when the sediment becomes too thick/heavy to move
- When sediment is frozen to the underlying bedrock.

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Glacial deposition

This happens when sediment is left behind by the glacier, often beneath it, or when the ice melts.

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Till (4)

- A poorly sorted, coarse sediment
- often with a bi-modal grain size distribution
- and a massive structure
- that is deposited in contact with a glacier - underneath it or next to it.

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Bi-modal grain size distribution (TILL)

Means that it has two sizes.

1. large (result of frost action)
2. small (result of abrasion)

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Massive structure (TILL)

all the grain sizes are uniformly mixed.

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What happens when till is deposited?

It forms a number of landforms

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Ablation till

Till deposited at the edge of a glacier

- Not compressed
- May show signs of having been reworked by running water

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Lodgment till

Till deposited beneath a glacier.

- It is compressed
- may be deformed by the ice passing over the top of it
- langara is built on lodgement till

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Glacial Landforms

- horns
- cirques
- u-shaped valley
- moraine
- truncated spur
- spur
- hanging valley
- drumlin
- col
- arete

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Moraines

Long linear ridges composed of till and deposited at the edge of a glacier.

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Types of moraine (4)

- lateral
- terminal
- recessional
- medial

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Terminal

Marks the furthest advance of the glacier.

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Recessional moraine

Marks the position of the front of the glacier during its retreat.

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Medial moraine

Form when two lateral moraines merge. Medial moraines are found "within" the glacier when two other glaciers merge.

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Moraines can be found in what settings? Differences?

Continental glacial and alpine glacial settings. In continental settings, moraines can be quite big.

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Moraines in continental settings

There are large till plains instead of well defined ridges that form moraines.

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Till plains

Area of land covered in till. They often have irregular or hummocky topography.

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Hummocky topography

Defined by many closely spaced highs and lows.

Result of different rates of deposition.