AS

dynamic planet glaciers

1. Glacier Formation

a. Properties of Ice

  • Crystal Structure: Ice in glaciers forms a hexagonal crystalline structure, aligning under pressure.

  • Density:

    • Fresh snow: ~0.05–0.2 g/cm³

    • Firn: ~0.4–0.83 g/cm³ (intermediate stage between snow and ice)

    • Glacial ice: ~0.83–0.917 g/cm³ (highly compacted, bubble-trapped ice)

b. Formation of Glacial Ice

  • Snow: Accumulated precipitation starts the process.

  • Névé: Older snow that has survived at least one melt season; partially compacted.

  • Firn: Transitional stage between snow and glacial ice; granular, partially compressed.

  • Glacial Ice: Formed when firn is compacted under pressure over time, expelling air and forming dense ice.

c. Glacial Budget / Mass Balance

  • Ablation: Loss of ice and snow through melting, sublimation, calving.

  • Accumulation: Addition of snow and ice through precipitation and avalanches.

  • Equilibrium Line (ELA): The line on a glacier where accumulation = ablation; above ELA the glacier grows, below it melts.

d. Glacial Flow

  • Basal Sliding: Ice slides over a thin layer of meltwater or deformable sediment at the base.

  • Internal Deformation: Ice deforms and flows plastically under its own weight.

  • Flow Rate Influenced by:

    • Bed conditions (e.g., rock vs. sediment)

    • Slope of glacier bed

    • Ice thickness and temperature

2. Types of Glaciers & Their Geographic Distributions

a. Valley/Alpine Glaciers

  • Form in mountainous regions, flow down valleys.

  • Cirque glaciers: Small glaciers occupying bowl-shaped hollows.

  • Hanging glaciers: Cling to steep mountain sides.

  • Piedmont glaciers: Spread out in a lobe at the base of a mountain.

b. Ice Sheet/Continental Glaciers

  • Ice Sheets: Vast, continental-scale glaciers (>50,000 km²); e.g., Antarctica, Greenland.

  • Ice Streams: Fast-flowing sections of ice sheets.

  • Ice Shelves: Floating extensions of ice sheets over ocean water.

  • Ice Rises: Domes of grounded ice within an ice shelf.

  • Ice Caps: Mini ice sheets; less than 50,000 km².

  • Ice Tongues: Narrow projecting glaciers that extend into the sea.

3. Features in Glacial Ice

  • Crevasses: Deep cracks in glacier surface due to brittle failure.

  • Ogives: Alternating bands of light and dark ice formed at base of icefalls due to seasonal flow variation.

  • Icefalls: Steep sections where glacier ice flows rapidly over a cliff or steep slope, often forming crevasses.

4. Ice Shelves and Related Processes

  • Calving: Breaking off of chunks of ice from glacier terminus into water.

  • Marine Ice Sheet Instability: Occurs when the bedrock beneath an ice sheet slopes downward inland, causing destabilization.

  • Ice Shelf Buttressing: Ice shelves act like a dam, holding back the flow of grounded ice into the ocean.

5. Formation of Landscape Features by Glaciers

a. Erosional Landforms

  • Cirque: Bowl-shaped hollow where glacier originates.

  • U-Shaped Valley: Formed by glacial erosion of river valleys.

  • Hanging Valleys: Smaller valleys left ‘hanging’ above the main U-shaped valley.

  • Arêtes: Sharp ridges between adjacent glacial valleys.

  • Horns: Pyramidal peaks formed by several cirques eroding a mountain (e.g., Matterhorn).

  • Striations: Scratches on bedrock from debris in basal ice.

  • Roche Moutonnée: Asymmetrical rock outcrops smoothed on the up-glacier side, plucked on the lee side.

b. Depositional Landforms

  • Moraines:

    • Terminal: Marks glacier’s furthest advance.

    • Recessional: Left behind as glacier retreats.

    • Lateral: Along the glacier’s sides.

    • Medial: Formed where two glaciers merge.

    • Ground: Blanket of till left under glacier.

  • Drumlins: Elongated hills of glacial till, streamlined in direction of ice flow.

  • Kames: Steep mounds of sand/gravel deposited by meltwater.

  • Eskers: Long, winding ridges formed by subglacial stream deposits.

  • Erratics: Large boulders transported far from their origin.

6. Glacial Lakes

  • Tarns: Small lakes in cirques.

  • Kettle Lakes: Formed by melting of buried ice blocks.

  • Finger Lakes: Long, narrow lakes in glacial valleys.

  • Moraine-dammed Lakes: Formed by meltwater trapped behind moraines.

  • Proglacial Lakes: Formed at glacier margins by meltwater.

7. Periglacial Processes and Landforms

  • Permafrost: Permanently frozen ground.

  • Pingos: Ice-cored hills caused by upward pressure of freezing groundwater.

  • Frost Heave: Soil displacement due to ice growth.

  • Frost Cracks / Ice Wedges: Cracks filled with ice that widen over time.

  • Frazil Ice: Needle-like ice crystals in supercooled turbulent water.

  • Pancake Ice: Circular ice forms in calm water; may raft into thicker layers.

8. Glacial Hydrology

  • Surface Melt: Water flows in streams across glacier surface.

  • Moulins: Vertical shafts connecting surface water to glacier base.

  • Subglacial Drainage: Water channels beneath glaciers influence ice movement.

  • Subglacial Lakes: Liquid water bodies under thick ice sheets (e.g., Lake Vostok).

9. Global Connections to Glaciation

a. Atmosphere

  • Greenhouse gases (CO₂, CH₄) increase melt rates.

  • Aerosols reduce surface albedo, increasing absorption of solar radiation.

b. Oceans

  • Glacial melt raises sea levels.

  • Freshwater influx alters ocean circulation.

c. Lithosphere

  • Isostatic Rebound: Crust rises after glacier retreats.

  • Affects regional uplift and tectonics.

d. Planetary/Orbital Influence

  • Milankovitch Cycles:

    • Eccentricity: Orbit shape (~100,000 years)

    • Obliquity: Axial tilt (~41,000 years)

    • Precession: Axis wobble (~26,000 years)

10. History of Ice on Earth

a. Neoproterozoic Snowball Earth

  • Global glaciation ~700 million years ago.

  • Equatorial dropstones support theory of global ice cover.

b. Late Paleozoic Ice Age

  • Major glaciation during Carboniferous-Permian.

  • Gondwana covered by large ice sheets.

c. Eocene-Oligocene Transition

  • Antarctic glaciation began ~34 million years ago.

  • Triggered by tectonic and ocean current changes.

d. Pleistocene Glaciation

  • Multiple ice ages over 2.6 million years.

  • Laurentide Ice Sheet covered much of North America.

e. Recent Changes

  • Modern glaciers retreating rapidly due to climate change.

  • Collapse of Larsen B, retreat of Thwaites Glacier.

11. Sedimentary Sequences in Glacial Environments

  • Till: Poorly sorted, unlayered sediment.

  • Outwash: Sorted sediment from glacial meltwater.

  • Varves: Annual lake sediment layers (summer = coarse, winter = fine).

  • Dropstones: Ice-rafted debris in fine sediment.

12. Methods of Studying Glaciers

  • Altimetry: Laser/Radar measures surface elevation change.

  • Radar (GPR/SAR): Reveals ice thickness and layering.

  • Optical Imagery: Monitors glacier retreat.

  • Seismology: Detects ice quakes and basal movement.

  • Gravimetry (GRACE): Tracks mass changes in ice sheets.

  • Ice Cores: Contain climate data (gases, isotopes, volcanic ash).

13. Glacial Hazards

  • Ice Avalanches: Large masses of ice fall rapidly; deadly in mountains.

  • Glacial Lake Outburst Floods (GLOFs): Sudden release of water from moraine/ice-dammed lakes.

  • Calving: Ice breaks off glaciers/ice shelves into water bodies, sometimes causing tsunamis.