Glaciers and Glacial Landforms

Glacier - Mass of ice that persists throughout the year.

• Accumulation and compaction of snow into ice.• Ice deforms and flows outward responding to gravity.• Flow generally from high to low altitude or high to low

latitude.• Ice advance stops where melting equilibrates with flow.• Retreat by melting.• Alpine glaciers - ice fills and flows down valleys.• Ice caps - ice covers mountain peaks.• Ice sheets - ice covers most of continent.

Snow falls

Ice movement in a glacier

Zone of accumulation Zone of wasting

eroded boulders

Ice melts

Snow falls

Ice movement in a glacier

Zone of accumulation Zone of wasting

compacts to ice

Ice melts

Snow falls

Ice movement in a glacier

Zone of accumulation Zone of wasting

compacts to ice

Ice flows

Ice melts

• If rate of accumulation is greater than melting, glacier will advance.

Flowing ice carves the landscape

Glacier advances

Snow falls

Ice movement in a glacier

Zone of accumulation Zone of wasting

Ice flows

Ice melts

• When rate of melting equals rate of accumulation, glacier stops advancing.• Equilibrium

Glacier stops advancing.

Snow falls

Ice movement in a glacier• in equilibrium, glacier does not appear to change position.• ice is always in motion.• ice accumulation equals ice melting.

Zone of accumulation Zone of wasting

terminus

Glacier acts like a conveyor belt, eroding and carrying rock, sediments, and soil to its terminus.

Snow falls

Ice movement in a glacier• If melting increases, glacier will retreat, even though ice is still flowing.• Rate of melting is greater than rate of accumulation.

Zone of accumulation Zone of wasting

moraine

Melting ice deposits rock and sediment.Glacial deposits create distinctive landforms.

Glacier retreats

Ice flows

Snow falls

Ice movement in a glacier• If melting increases, glacier will retreat, even though ice is still flowing.• Rate of melting is greater than rate of accumulation.

Zone of accumulation Zone of wasting

moraine

Melting ice deposits rock and sediment.Glacial deposits create distinctive landforms.

Glacier retreats

Ice flows

Zone of accumulation(more snow falls then melts per year)

Zone of ablation (wastage)(more melting than snowfall)

Glaciers - agents of erosion• Glaciers are highly effective agents of erosion.

• Abrasion - rock debris embedded in base of ice.• Polishing, grooves and striations.

• Plucking / Quarrying - removal of large chunks of rock debris.

Bedrock surface polished by glacial ice.

Glaciers - Erosional Landforms• Cirque - semicircular hollow with steep headwall carved

by glaciers into an alpine valley head.

Glaciers - Erosional Landforms• Arete - steep, knife-edge ridge between glacial valleys.• Col - gap in an arete where two cirques meet.• Horn - steep peak carved out by cirques.

Glaciers - Erosional Landforms• Glacial trough - wide, parabolic valley carved by ice

flow (also called a “U-shaped” valley).

Mountains during glaciation

Mountains after glaciation

Norway Hudson River

Fjiord - glacially carved valley flooded by the sea.

Glacial Striations - linear glacial scratch marks on bedrock.

Glaciers - Agents of Deposition

• Glaciers are highly effective agents of deposition.• Drift - rock debris deposited by glaciers.• Glacial Lake Deposits - pebble, sand, clay and silt

sediments accumulated in meltwater lakes.• Loess - very fine, wind-blown rock flour.

Till - Nonstratified, poorly sorted drift deposited directly from glacial ice.

Stratified drift - sorted, layered sediments deposited by glacial meltwater - outwash.

Glaciers - Depositional Landforms

• Ice contact deposits - sediments melted directly out from the ice.

• Outwash deposits - sediments deposited by meltwater flowing from the ice.

Kame - mound of till released by melting ice.

Esker - Manitoba

Esker - serpentine ridge of stratified drift deposited inside of ice meltwater tunnel.

Drumlin - tear-drop-shaped hill created by ice flow over and around till deposit.

Drumlins - Manitoba

Moraine - linear ridge of till deposited at ice margin.

Glaciers - Depositional Landforms

• Outwash features - deposition by meltwater in the outwash plain (region in front of ice receiving flow of meltwater).

• Erratics - boulder size and larger blocks of rock deposited by melting glacial ice.

Landscape during glaciation

Kettles - depressions formed as stranded ice blocks melt in outwash.

Landscape after glaciation

Kettles - depressions formed as stranded ice blocks melt in outwash.

Outwash plain in front of moraine.

moraines

kettle

kame

outwash

Features of a glacial moraine

Ice Caps and Ice Sheets - unconfined by topography.

• Ice Cap - less than 50,000 km2.• Ice Sheet - cover major portion of a continent.• Ice thicker than topography.• Ice flows in direction of slope of the glacier.• Greenland and Antarctica - 3000 to 4000 m thick (10 -

13 thousand feet or 1.5 to 2 miles!)

Alpine Glaciers - developed on mountain peaks and valleys.

• Cirque glacier - small glacier occupying valley head.• Valley glacier - river-like glacial occupying valley.• Piedmont glacier - valley glacier that flows out onto

the flatlands.• Fjord glacier - valley glacier with base below sea

level.• Ice field - region of interconnected alpine glaciers.

Piedmont Glaciers - lobate lowland glacier fed by alpine glaciers .