Glaciers and Glacial Landforms Notes

GEOG 4700: Geomorphology - Glaciers and Glacial Landforms Homework Notes

I. Glaciers

  • Formation of Glacier Ice

    • A newly deposited snowflake undergoes several stages before becoming glacier ice:
    • Snowflake Stage: Intricate form of the snowflake is preserved initially.
    • Granular Snow Stage: Snow transforms as it gets buried and compacted, leading to decreased porosity and increased density.
    • Firn Stage: Snow experiences slight diameter increase as it continues to compact.
    • Glacier Ice Stage: Final transformation into solid and dense glacier ice.

  • Glacial Advance and Retreat

    • Mass Balance: The relationship between mass gains and losses determines glacier thickness.
    • Advance: Occurs when mass gains (e.g., wind drifting, snowfall, avalanching) exceed losses.
    • Retreat: Happens when mass losses (e.g., sublimation, evaporation, calving) exceed gains, leading to thinning.

  • Glacier Movement

    • Ice Creep: Slow internal deformation of ice ensures gradual movement.
    • Basal Sliding: Involves sliding at the bed-ice interface, enhancing glacier flow.
    • Deformation of a Mobile Bed: Glacier movement over slowly deforming sediment beneath the ice.

  • Cold-based vs. Warm-based Glaciers

    • Cold-based Glaciers:
    • Remain frozen to their base, causing slower movement at the bed and faster at the top.
    • Do not erode underlying sediment.
    • Warm-based Glaciers:
    • Not frozen to the bed, allowing sliding and more dynamic movement (ice creep).
    • Greater erosion capacity, actively removing sediment.

II. Glacial Landforms

  • Eskers

    • Elongate, sinuous ridges composed of sorted sediment deposited by water, often capped and underlain by glacial till.

  • Kettles

    • Circular depressions near former ice margins resulting from sediment subsidence after buried ice melted.

  • Outwash Plains

    • Gently sloping surfaces formed by glacial meltwater streams, often pitted with kettles and underlain by sand and gravel.

  • Kames

    • Mounds of sediment, roughly circular, deposited from depressions on the glacier’s surface when melted.

  • Drumlins

    • Streamlined, elongated hills pointing in the direction of ice flow, may consist entirely of sediment or have a rock core.

  • Terminal Moraines

    • Piles of glacial till deposited at the glacier's distal end, resulting from melting in the ablation zone.

  • Lateral Moraines

    • Deposits along the sides of the ablation zone of alpine glaciers, formed from debris rolling off or melting out of ice.

  • Medial Moraines

    • Formed by merging lateral moraines of two tributary glaciers into a singular concentration of debris.

  • Till Plains

    • Featureless surfaces underlain by glacial till, created when ice melts too rapidly, preventing the formation of defined moraines.

  • Dropstones

    • Large rocks found in fine-grained sediment of glacial lakes, which sank after the floating ice that carried them melted away.