GLACIAL EROSION AND DEPOSITION

GLACIAL EROSION

As glaciers travel over land, glacial ice can erode the underlying bedrock.

This erosion can happen by: Plucking

Abrasion

PLUCKING

This occurs when melt water at the base of the glacier freezes in cracks and fractures the underlying bedrock.

The fractured materials are then pulled away from the bedrock.

The weathered material then becomes incorporated into the glacial ice and undergoes transportation as the glacier moves.

Glacial ice also picks up loose boulders , pebbles, and sand from the underlying surface as it moves.

ABRASION

This is the grinding or scouring of exposed rock surfaces by rock fragments embedded in the base of the glacier.

Think of this a being the sandpaper effect

The dislodged pieces of rock become part of the glacial ice.

The abraded bedrock surfaces generally show a polished look and display striations or grooves caused by the sediment embedded in glacial ice.

The abraded material can become pulverized to yield a fine clay or silt material called rock flour

CONTOURS

Continental glaciers only erode on the bottom, and just flatten out the topography

Valley glaciers erode along their sides and on the bottom.

The shape of the valley as the glacier moves downhill is that of a U-shape or glacial trough.

These valley glacier give us many unique features based on the size and location.

Fjords Hanging valleys Cirques Horns Arêtes

Fjords

Glacial formed valleys filled with seawater.

Hanging valleys

A U-shaped valley not as deep as the main valley.

Cirques

A three sided bowl shaped depression where valley

glaciers begin.

Horns

A sharp mountain peak formed adjoining cirques

Arêtes

Sharp ridges which join adjacent horns and adjacent cirques

DEPOSITION

The material moved by a glacier eventually is deposited as the glacier melts.

All sediment that is deposited by a glacier is termed glacial drift.

There are two types of glacial drift: Till, and Outwash

TILL

This is the material that is deposited directly by glacial ice and is a mix of sediment particles of various sizes.

Large boulders of drift that are moved far from their bedrock source are called erratics.

As a valley glacier moves downhill, it erodes material at the glacier’s sides and base and forms distinct features made of till. These features are called moraines.

End Moraine – contains the glacial till at the toe of a glacier

Ground Moraine – are a term for a moraine at the base of the glacier

Lateral Moraines – are the deposited till along the sides of a glacier.

When two glacier with lateral moraines merge their lateral moraines join in the center of the merged glacier to form medial moraines in the central portion of the glacier

Till deposited at the base of a glacier can be reshaped by successive glacial movements into streamlined mounds of till called drumlins.

OUTWASH

This is material that deposited by melt water from a glacier and is similar to a stream deposit, with larger fragments deposited by waters flowing with greater velocity and finer fragments deposited by slower moving water.

During warm weather or periods of retreat, glaciers discharge melt water at their toe or terminus. The area created by the deposition of sediment from flowing melt water from a glacier is called the outwash plain.

Melt water can form a meandering streams at the base of a glacier. These streams create sinuous ridges of sediment called eskers.

During a retreat a large chunk of ice remains behind which depresses the land and melts to form a kettle lake.

Esker located in SW Nova Scotia

Kettle lakes