DYNAMIC PLANET

Glacier Formation

• Glacier Formation Process:

  1. Snowfall accumulates in cold regions and persists year-round.

  2. Repeated melting, refreezing, and compaction transform snow into neve (granular snow) and then firn (densely packed snow).

  3. Over decades, firn compacts into glacial ice through pressure and recrystallization.

2. Properties of Ice

• Crystal Structure:

  • Ice forms hexagonal crystals.

  • Arrangement determines strength, flow characteristics, and transparency.

• Density:

  • Snow: ~50–300 kg/m³

  • Firn: ~550 kg/m³

  • Glacial Ice: ~830–917 kg/m³ (density increases with compaction).

3. Glacial Budget or Mass Balance

• Key Terms:

  • Accumulation: Addition of snow and ice (precipitation, avalanches, rime ice).

  • Ablation: Loss of ice via melting, sublimation, calving, or wind erosion.

  • Equilibrium Line Altitude (ELA): Marks the boundary where accumulation equals ablation.

• Positive Budget: Glacier advances.

• Negative Budget: Glacier retreats.

4. Glacial Flow

• Types of Flow:

  • Internal Deformation: Ice crystals slide past each other under pressure.

  • Basal Sliding: Glacier moves over a lubricated bed of meltwater.

• Relation to Elevation and Slope:

  • Steeper slopes and higher elevations lead to faster glacial flow.

  • Flow is fastest at the surface and center due to reduced friction.

5. Types of Glaciers and Geographic Distributions

• Valley/Alpine Glaciers:

  • Found in mountainous regions.

  • Types:

    • Cirque Glaciers: Occupy bowl-shaped depressions.

    • Hanging Glaciers: End at steep cliffs.

    • Piedmont Glaciers: Spread out at the base of mountains.

• Ice Sheets/Continental Glaciers:

  • Cover large areas (e.g., Antarctica, Greenland).

  • Associated Features:

    • Ice Streams: Fast-moving channels within ice sheets.

    • Ice Shelves: Floating extensions of glaciers.

    • Ice Caps: Smaller than ice sheets, dome-shaped.

    • Ice Tongues: Glaciers extending into the ocean.

6. Features in Glacial Ice

• Crevices: Deep cracks in the brittle surface of glaciers caused by stress.

• Ogives: Alternating bands of light and dark ice; linked to seasonal flow.

• Ice Falls: Regions of steep glacier descent resembling frozen waterfalls.

7. Shelves and Related Processes

• Calving: Icebergs break off from ice shelves into the ocean.

• Marine Ice Sheet Instability: Ocean warming causes basal melting, destabilizing the ice sheet.

• Ice Shelf Buttressing: Ice shelves stabilize inland glaciers by acting as a barrier to flow.

8. Formation of Landscape Features by Glaciers

Erosional Features:

• Cirques: Bowl-shaped hollows carved by glaciers.

• U-Shaped Valleys: Formed as glaciers erode valley walls.

• Hanging Valleys: Tributary valleys left "hanging" above the main valley.

• Aretes: Sharp ridges between adjacent glacial valleys.

• Horns: Pointed peaks formed by glacial erosion on all sides (e.g., Matterhorn).

• Striations: Grooves in bedrock made by rocks embedded in ice.

• Roche Moutonnée: Smooth, asymmetrical bedrock features shaped by glaciers.

Depositional Features:

• Moraines:

  • Lateral: Along glacier sides.

  • Medial: At the intersection of two glaciers.

  • Terminal: At the glacier's furthest extent.

  • Recessional: Formed as a glacier retreats.

  • Ground: Deposits left under a glacier.

• Kames: Mounds of sediment deposited by meltwater.

• Drumlins: Streamlined hills of till shaped by glacier movement.

• Eskers: Long, winding ridges of sediment from subglacial rivers.

• Erratics: Large boulders transported by glaciers.

Glacial Lakes:

• Tarns: Small lakes in cirques.

• Great Lakes & Finger Lakes: Glacially carved basins filled with water.

• Kettles: Depressions left by melting ice blocks.

• Moraine-Dammed Lakes: Formed when moraines block drainage.

• Proglacial Lakes: Formed in front of glaciers by meltwater.

9. Periglacial Processes and Landforms

• Permafrost: Permanently frozen ground.

• Pingos: Ice-cored hills formed by groundwater freezing.

10. Sea Ice

• Types:

  • Frazil Ice: Needle-like crystals forming in calm water.

  • Pancake Ice: Circular slabs formed in turbulent water.

• Key Features:

  • Draft vs. Freeboard: Submerged vs. above-water portions.

  • Pressure Ridges: Formed by ice collision and deformation.

11. Glacial Hydrology

• Surface Melt and Lakes: Seasonal melting forms supraglacial lakes.

• Moulins: Vertical shafts transporting meltwater to the glacier base.

• Subglacial Lakes: Lakes beneath glaciers, such as Lake Vostok.

12. Global Connections of Glaciation

Atmosphere:

• Greenhouse Gases: CO₂ and CH₄ release from melting ice enhances warming.

• Albedo Effect: Loss of reflective ice accelerates melting.

Oceans:

• Sea Level Change: Ice sheet growth lowers sea level; melting raises it.

• Thermohaline Circulation: Affected by freshwater influx from ice melt.

Lithosphere:

• Isostatic Rebound: Land rises after glaciers melt.

Planetary and Orbital Influence:

• Milankovitch Cycles: Orbital changes affect solar insolation, driving glacial cycles.

13. History of Ice on Earth

• Neoproterozoic (Snowball Earth): Evidence of global glaciation (~720–635 Ma).

• Late Paleozoic Ice Ages: Linked to supercontinent formation (e.g., Gondwana).

• Eocene-Oligocene Transition: Cooling due to Drake Passage opening (~34 Ma).

• Pleistocene Glaciation: Laurentide Ice Sheet dominated North America; retreat began ~20,000 years ago.

14. Sedimentary Sequences in Glacial Environments

• Varves: Annual layers of sediment deposited in glacial lakes.

• Outwash: Sorted sediments from glacial meltwater.

• Till: Unsorted, unstratified debris deposited directly by glaciers.

15. Methods of Studying Glaciers

• Altimetry: Measures ice surface height changes.

• Radar: Reveals ice thickness and subglacial topography.

• Optical Imagery: Tracks glacier movement via satellite photos.

• Seismology: Detects subglacial processes like icequakes.

• Gravimetry: Maps variations in Earth's gravity to estimate ice mass.

16. Glaciers as Archives of Past Environments

• Ice Cores:

  • Contain gases (CO₂, CH₄) and aerosols that indicate past climates.

  • Stable isotope ratios (e.g., O¹⁸/O¹⁶) reveal temperature history.

17. Glacial Hazards

• Ice Avalanches: Sudden ice fall from glaciers.

• Glacial Lake Outburst Floods (GLOFs): Catastrophic draining of dammed glacial lakes.