Glacier Formation Process:
Snowfall accumulates in cold regions and persists year-round.
Repeated melting, refreezing, and compaction transform snow into neve (granular snow) and then firn (densely packed snow).
Over decades, firn compacts into glacial ice through pressure and recrystallization.
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).
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.
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.
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.
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.
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.
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.
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.
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.
Permafrost: Permanently frozen ground.
Pingos: Ice-cored hills formed by groundwater freezing.
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.
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.
Greenhouse Gases: CO₂ and CH₄ release from melting ice enhances warming.
Albedo Effect: Loss of reflective ice accelerates melting.
Sea Level Change: Ice sheet growth lowers sea level; melting raises it.
Thermohaline Circulation: Affected by freshwater influx from ice melt.
Isostatic Rebound: Land rises after glaciers melt.
Milankovitch Cycles: Orbital changes affect solar insolation, driving glacial cycles.
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.
Varves: Annual layers of sediment deposited in glacial lakes.
Outwash: Sorted sediments from glacial meltwater.
Till: Unsorted, unstratified debris deposited directly by 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.
Ice Cores:
Contain gases (CO₂, CH₄) and aerosols that indicate past climates.
Stable isotope ratios (e.g., O¹⁸/O¹⁶) reveal temperature history.
Ice Avalanches: Sudden ice fall from glaciers.
Glacial Lake Outburst Floods (GLOFs): Catastrophic draining of dammed glacial lakes.