GEOL101: Glaciers

How do glaciers form?

From accumulation, compaction, and recrystallization of snow into ice over time.

Where are glaciers found today?

Polar regions (Antarctica, Greenland) and high mountains worldwide.

What is the common characteristic of where glaciers are found?

Cold climate or high elevation where snow persists year

About how much of Earth's surface is covered by glaciers today?

~10%.

In what direction does the ice flow when a glacier is advancing?

Forward, extending beyond its previous position.

In what direction does the ice flow when a glacier is retreating?

Ice still flows forward, but melting exceeds accumulation, so the terminus moves back.

In what direction does the ice flow when a glacier is neither advancing nor retreating?

Ice flows forward at the same rate as melting; terminus is stationary.

What landscape features are created by glaciers?

• U-shaped valleys

• Cirques

• Fjords

• Moraines

• Drumlins

• Eskers

What do glacier-carved valleys look like

U-shaped (steep sides, flat bottom)

What are glacial striations?

Scratches or grooves on bedrock caused by rocks embedded in moving ice.

Which type of glacial deposits are well sorted and which are poorly sorted?

Well-sorted: Outwash plains (sorted by meltwater)

Poorly-sorted: Till (directly deposited by ice)

Glaciers

• Thick ice masses

• Originate from snow

• Form on land

• Move slowly

• Part of the hydrologic cycle

  • 10% of earth’s land surface

• Significant water reservoirs

Types of glaciers

Valley (alpine), ice caps, ice sheets.

Valley glaciers

High altitudes, bounded by rock walls, flow down-valley

Ice caps

• Large, dome-shaped glacier

• Move (flow) outward in all directions from one or more snow-accumulation centers

Ice sheets

• Continent-scale mounds of ice

• Exist today only at high latitudes

  • Greenland

  • Antarctica

• Move (flow) outward in all directions from one or more snow-accumulation centers

• EX: greenland ice sheet flow

Glacier formation

• Form in regions where snow accumulates faster than lost, compacts, recrystallizes into ice

• ice grains compact as new snow added

Terminus

• Forward end of glacier

• can advance, retreat, or remain stationary.

Most valley glaciers

Currently retreating; some advancing or stationary.

Glacier always move _____ even when fronts (termini) are retreating

forward

Erosion by glaciers

Effective erosion agents; carry huge blocks of material.

Entrainment

Erosion of sediment & large debris.

Plucking

Loosening & lifting fractured rock.

Abrasion

Scraping by ice & rock fragments.

Landforms created from erosion by valley glaciers

• Glacial valleys

  • Hanging valleys

• U-shaped valleys

  • Cirques

    • Bowl-shaped depression w/ steep sides

• Horns

  • Sharp-edged pyramids

• Aretes

  • Sharp-edged ridges

• Fiords (fjords)

  • Glacial valleys flooded w/ sea water

Landforms created from erosion by ice sheet/ice cap glaciers

• Drumlins

  • Elongated hills

  • Usually composed of sediment

• Roche Moutonnee

  • Small, streamlined bed rock hill

Erosion by glaciers

• Other signatures of erosion by glaciers

  • Glacial striations

  • Grooves

2 ways glacial materials can be transported

• By the glacier

• By glacial meltwater

Glacial transport

By glacier & meltwater.

Glacial till

• Materials transported and deposited directly by glacier

• Poorly sorted

• Sometimes show scratch marks

• Different names are used for till deposits based on “how” and “where” of deposition

  • Lateral moraines

  • Medial moraines

  • End moraines

  • Ground moraines

Stratified drift

• Materials transported and deposited by glacial meltwater

  • Outwash plains

    • Sediment deposited by meltwater from ice sheet

  • Valley trains

    • Sediment deposited by meltwater from valley glacier

  • Eskers

    • Sinuous ridges of sand and gravel

  • Kames

    • Hills of sand and gravel

Kettles

Depressions formed when ice block buried in sediment melts.

2 categories of glacial deposits

• glacial till

• stratified drift

Glacier fronts (termini) depend on 

• Net gain, or

• Net loss, or

• Balance btw gain and loss

• Of ice at termini