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.