Glaciers and Glaciation

Glaciers are thick ice masses that originate on land from the accumulation, compaction, and recrystallization of snow. Glaciers are part of the hydrologic cycle. Glaciers account for 2% of the world’s water.

Glacier Types 1. Valley (Alpine) Are confined to mountain valleys. They are smaller than ice sheets, and only cover a small region.

Alpine Glaciers Not in notes.

2. Ice sheets (Continental glacier) Glacier Types 2. Ice sheets (Continental glacier) Are large scale. They are not confined to valleys. They cover 10% of Earth’s land and can be 1 500 m or more thick! Greenland – 1.7 million km2 Antarctica – 15.5 million km2

Continental Glaciers Some parts are more than 25 000 years old. Not in notes.

Continental Glaciers If all of Antarctica’s ice melted then: sea level would rise 60 to 70 m it would provide enough water to feed the Amazon River for 5 000 years and all of the world’s rivers for 750 years. Not in notes.

Formation of Glacial Ice From Snow From fluffy snow to crystallized grains.

Formation of Glacial Ice From Snow A change in shape of snowflakes occurs. They become smaller, thicker, and more spherical as a result of evaporation and condensation. As a result, air space decreases and the snow recrystallizes into a more dense mass of small grains called firn.

As more snow is added the pressure increases causing compaction. When the thickness exceeds 50 m, firn is fused into a solid mass of interlocking ice crystals.

Not in notes.

Glacier Movement Two types: 1. Plastic Flow. Normally ice behaves as a brittle solid. But when it is 50 m or more thick it behaves as a plastic material. Layers within the ice slide past each other.

2. Basal Slip. When the entire ice mass slips along the ground. Meltwater is thought to act as a lubricant helping ice flow over rock. As pressure increases, melting point decreases, so there can be liquid water at temperatures below 0°C

The rate of movement is not uniform throughout. Frictional drag slows the movement. Friction is greatest at the base of the glacier. Friction is also high along valley walls.

Glacier Movement

Glacier Movement The uppermost zone of ice (< 50 m deep) remains brittle. This is the zone of fracture. Ice here is carried by movement below. Tension forces can cause cracking and the formation of crevasses up to 50 m deep.

Pollution Sampling

Even though the ice front was retreating, the ice within the glacier was still advancing! Glacier Movement Not in notes. Rhode Glacier, Switzerland

Glacier Budget In Out Zone of accumulation: - Snow Ablation – loss of ice or snow : - Melting - Calving - icebergs

Glacier Budget

glacier “budget” snowline zone of wastage calving Balance between accumulation at upper end & loss (“ablation”) at lower end Lower limit of “zone of accumulation” Net loss (melting) Large ice pieces break off Not in notes.

Large ice pieces break off calving

Glacier Erosion Occurs in two ways: Plucking – the loosening and lifting blocks of rock and incorporating them into the ice (frost wedging plays a major part) Abrasion – ice and its load act like sandpaper scraping the bedrock surface (resulting grit is called rock flour)

plucking

Glacier Erosion Striations – grooves can result from debris that is carried by the ice scratching into the bedrock. Striations show the direction of ice movement. Rock polishing – can result from the movement of fine grit over bedrock

abrasion - glacier+rock fragments scrape over bedrock Not in notes.

Rate of Erosion Depends on: Rate of glacial movement Thickness of ice Shape, abundance, and hardness of rock fragments carried Susceptibility of surface to erosion

Glacial Landforms Valley Glaciers – tend to accentuate the landscape. Ice Sheets – tend to subdue the landscape. Glaciers take the path of least resistance by following existing stream valleys.

V-shaped river valleys become U-shaped glacial troughs. Pater noster lakes Or rock basin lakes

Main glaciers cut deeper than tributary glaciers because they are thicker. When the glaciers recede, hanging valleys are formed.

As ice flows around sharp curves, spurs of land extending into the valley are removed forming truncated spurs. Truncated spurs – are eroded triangular- shaped cliffs in previously glaciated valleys.

Arete – is a narrow , knifelike ridge separating two adjacent glaciated valleys.

Cirque – an amphitheatre-shaped basin at the head of a glaciated valley. It is the area of snow accumulation and ice formation. Tarn – a small lake in a cirque.

Horn – a pyramid-like peak formed by glacial action in three or more cirques surrounding a mountain summit. Matterhorn in the Swiss Alps

Valley Glaciers Not in notes.

Glacial Deposits The bedrock in many areas is buried under tens or even hundreds of metres of till from past continental glaciation. Glacial deposits are largely mechanically weathered rock rubble. Little chemical weathering prior to deposition would have occurred.

Two distinct types Till – material deposited directly by the glacier. It consists of unsorted sediment. Sorted Sediments – material laid down by glacial meltwater

Till Deposits Moraine - a pile of debris that has been transported and deposited by a glacier Erratics – are boulders left on the surface after the ice has melted

end moraine: ridge of till at the end of stable glacier recessional moraine: all other end moraines other than the terminal moraine lateral moraine: debris on the sides of glacier medial moraine: forms where two lateral moraines join

Not in notes.

Terminal Moraine – is the furthest reaching debris that is pushed along in front of the glacier Ground Moraine - debris accumulated under the glacier A kettle lake forms when a depression left by a chunk of ice fills with water.

Ground moraine has a leveling effect – filling in low spots, clogging stream channels, and causing a destruction of any existing drainage system. Ground Moraine

Formation of a Terminal Moraine Not in notes.

What type of moraine is this? Not in notes.

What type of moraine is this? Not in notes.

What is this feature called? Not in notes.

Drumlins Smooth elongated parallel hills formed from continental ice sheets. They occur in clusters called drumlin fields. Thought to be formed in the plastic zone from the reshaping of previously deposited glacial till.

Not in notes.

Sorted Sediment Deposits Kettles (can also occur in till deposits) Outwash plains Kames Eskers

Kettle Lakes

Outwash Plain – As meltwater leaves a glacier and moves to flatter ground, velocity decreases and sediment is dropped. Braided channels eventually form.

Not in notes.

Kame – mound of well-sorted till

Esker – long, narrow, sinuous ridge of sorted sand and gravel deposited by meltwater rivers flowing in confined channels within, on top of, and beneath a mass of motionless ice.

Not in notes.

How would you know that this valley was not carved by the river which flows in it today?