Ch 17 Glacial Landscapes slides

Chapter 17: Glacial and Periglacial Landscapes

Introduction to Glacial Landscapes

  • Dome Glacier in fore field, Columbia Icefield (Photo taken during UFV Adventures in Geography trip June 2019).

Learning Objectives

  • Explain how snow transforms into glacial ice.

  • Differentiate between alpine glaciers and continental ice sheets; describe ice caps and ice fields.

  • Describe the mechanics of glacial movement.

  • Identify unique erosional and depositional landforms created by glaciation.

  • Discuss landscapes from the Pleistocene ice age epoch and ongoing changes in polar regions.

Overview of Glaciers

  • Cover 11% of Earth's surface currently; can cover up to 30% during glacial periods.

  • Pleistocene ice sheets extended significantly 18,000 years ago in the Northern Hemisphere.

Importance of Glaciers

  • Comprise approximately 77% of Earth's freshwater.

  • Formed by accumulation, compaction, and recrystallization of snow over thousands of years.

  • Can flow similar to streams; important for climate indication and erosion.

Formation of Glacial Ice

  1. Stage 1: Snow survives summer.

  2. Stage 2: In winter, old snow compressed into firn (granular texture).

  3. Stage 3: Over time, snow/firn → glacial ice (recrystallization and metamorphism).

  • Glaciers form in locations with more snow accumulation than melting.

Types of Glaciers

1. Alpine Glaciers

  • Situated in mountain ranges, varied lengths.

  • Subtypes Include:

    • Cirque Glacier: Bowl-shaped recess occupying valley heads.

    • Valley Glacier: Extends from cirque glaciers into existing valleys.

    • Piedmont Glacier: Spreads out from valley into lowlands.

    • Tidewater Glaciers: End in sea bodies influenced by tides.

2. Continental Glaciers

  • Larger than alpine glaciers; Ice Sheet: Mass covering >50,000 km² (Antarctic, Greenland).

  • Dome-shaped with ice flowing in all directions from accumulation areas.

  • Associated features include ice caps (circular, <50,000 km²) and ice fields (elongated).

Glacial Mass Balance

  • Two Zones:

    • Accumulation Zone: Inputs > Outputs (ice formation area).

    • Ablation Zone: Outputs > Inputs (ice loss via melting).

  • Equilibrium Line: Where accumulation equals ablation.

  • Important for monitoring climate change; positive mass balance leads to glacier advancement.

Mechanics of Glacial Movement

  • Movement due to:

    • Internal Deformation: Ice deforms under pressure (plastic flow).

    • Basal Flow: Ice slides on underlying rock, aided by meltwater.

    • Variations in movement speed (faster in glacier center due to friction).

Glacial Erosion

  • Methods:

    • Plucking: Lifts and removes rock blocks from bedrock.

    • Abrasion: Sandpaper effect smooths surfaces; creates glacial polish, striations.

    • Transports debris in several ways (on surface, internally).

Erosional Landforms

  • Transformation of V-shaped valleys into U-shaped troughs.

  • Formation of features such as:

    • Cirques: Bowl-shaped depressions.

    • Arêtes: Sharp ridges between cirques.

    • Fjords: Submerged U-shaped valleys.

    • Rochelle Moutonnée: Asymmetrical hills formed by glacial action.

Depositional Landforms

  • Types of Sediment Deposits:

    • Till: Unsorted, unstratified sediments.

    • Glacial Erratics: Large rocks transported and left by glaciers.

  • Moraines: Till landforms indicating glacier extent.

    • Types: Lateral, medial, terminal, and recessional moraines.

Glaciation Comparisons

  • Erosional and depositional features differ between alpine and continental glaciers:

    • Glaciers create unique landforms like striations, cirques (both common in alpine), while U-shaped valleys are typical of alpine glaciers and rare for continental.

The Pleistocene Epoch

  • Spanned approximately 2.6 million years ago to 10,000 years ago; defined by glaciation periods.

  • Glacial advances altered landscapes and soil composition significantly in regions like Canada.

Causes of Glaciations

  • Astronomical changes influencing climate (Milankovitch cycles):

    • Eccentricity: Variations in Earth's orbit.

    • Precession: Axis wobbling affecting seasonal distribution.

    • Obliquity: Variations in axial tilt impacting seasonal climate.

Modern Polar Changes

  • Current trends show decreasing ice extent and increased melt, influencing ecosystems and climate.

  • Implications for shipping routes and environmental shifts due to climate change.