Lecture 3 Part 1 - Glacial Landscapes (with audio lecture)

Lecture 3: Glacial Landscapes

Overview

  • Focus on glacial landscapes and their historical context.

Geological Timeline

  • Era: Major divisions of geological time.

  • Period: Specific durations within an era.

  • Epoch: Smaller divisions within a period.

Key Geological Timeframes

  • Cenozoic Era: Age of mammals.

    • Tertiary Period: Pliocene, Miocene, Oligocene, Eocene, Paleocene.

    • Quaternary Period: Holocene (Recent), Pleistocene.

  • Mesozoic Era: Age of reptiles.

    • Jurassic, Triassic, Permian.

  • Paleozoic Era: Early life forms.

    • Mississippian, Devonian, Silurian, etc.

Ice Ages

  • Quaternary Glaciation: 2.75 million years ago to present.

  • Five notable glacial periods throughout geological history:

    • Huronian (2.4 to 2.1 billion years ago).

    • Andean-Saharan (460 to 420 million years ago).

    • Karoo Ice Age (360 to 260 million years ago).

    • Cryogenian (850 to 630 million years ago).

The Last Ice Age: The Pleistocene Epoch

  • Definition: Began approximately 2.6 million years ago, ending about 11,700 years ago.

  • Extent: Covered nearly a third of Earth’s surface; a significant habitat for early Homo sapiens, who spread across the globe during this time.

Ice Sheets in North America

  • Three Major Ice Sheets during the Pleistocene:

    • Greenland Ice Sheet

    • Laurentide Ice Sheet

    • Cordilleran Ice Sheet

Characteristics of Snow

  • Each snowflake is unique and varies by temperature and humidity.

  • Snow can accumulate or melt upon contact with the Earth's surface and forms layers like sedimentary rock.

From Snow to Glacial Ice

  • Snowline: Minimum elevation with year-round snow retention.

    • Examples: Equatorial 5000 m, Mid-latitude 2700 m, Southern Greenland 600 m.

  • Formation: Glaciers form when snow recrystallizes into ice under its own weight.

Glacial Ice: Mineral and Rock

  • Defined as both a mineral (inorganic natural compound) and a rock (mass of minerals).

  • Recrystallization: Forms metamorphic rock; progression:

    • Snow → Firn (granular snow) → Ice.

Deserts of Antarctica and the Arctic

  • Definition of a Desert: Regions with annual precipitation below 250 mm (10 inches).

  • Glacial ice can take up to 1000 years to develop.

Types of Glaciers

  • Glaciers: Large ice masses moving under their weight.

    • Two Main Types:

      • Alpine Glaciers: Found in mountainous regions.

      • Continental Ice Sheets: Large ice masses on a continental scale.

Alpine Glaciers

  • Different forms of alpine glaciers:

    • Valley Glaciers: Flow within valleys.

    • Cirque Glaciers: Identify at valley heads.

    • Piedmont Glaciers: Result from the coalescence of multiple valley glaciers.

Continental Ice Sheets

  • Cover large land areas; all Earth's glacial ice mostly held here.

  • Comprise 81% of Greenland and 90% of Antarctica; can be up to 2-3 km thick.

Ice Caps and Ice Fields

  • Ice Caps: Smaller than ice sheets, roughly circular, often atop volcanoes.

  • Ice Fields: Elongated ice formations over mountainous regions (e.g., Kluane Icefield).

Glacial Areas in Canada

  • Divided into three regions:

    • Coastal - Beginning from the Pacific.

    • Arctic - Including North Canada's vast lands.

    • Rocky Mountain - Heavily glaciated regions.

Mechanics of Glacial Movement

  • Movement driven by mass; continual motion.

  • Glacial Equilibrium: Balance between incoming snow and melting rate.

  • Terminus: Edge of glaciers, notable for expansion or retreat.

Mass Balance of Glaciers

  • Mass Balance: Calculates gain/loss of glacier ice.

    • Negative Balance: More loss leads to retreat.

    • Positive Balance: Gains indicate expansion.

    • Equilibrium: Balance between gains and losses.

Understanding Equilibrium Line Altitude

  • Accumulation Zone: Area with net gains.

  • Ablation Zone: Area with net losses; marks the equilibrium line altitude where accumulation equals ablation.

Ablation: Loss of Glacier Mass

  • Methods of ablation:

    • Melting (surface, internal, basal)

    • Deflation by wind

    • Calving of ice blocks

    • Sublimation directly from solid to vapor.

Anatomy of a Glacier

  • Structure:

    • Rigid at the top, pliable at the base.

    • Flow via internal fracture and basal slip.

  • Notable phenomena: formation of crevasses.

Glacial Erosion Processes

  • Debris Functionality: Glaciers pick up debris through melting and refreezing.

  • Processes: abrasion (smooths and polishes landscape) and glacial plucking (removes bedrock).

Depositional Landforms

  • Glacial Erratics: Large boulders left behind post-glacier retreat, e.g., Okotoks Erratic (16,500 tons).

  • Formed as part of geological features like moraines and kettle lakes.

Types of Deposits

  • Moraines: Accumulation of debris from glaciers.

    • Types include terminal, lateral, and medial moraines.

  • Till Plain: Unsorted sediment deposits behind glaciers.

  • Drumlins: Teardrop shapes formed by glacial movement, pointing to the ice flow direction.

  • Outwash Plains: Formed from glacier melt, consisting of sediment stratification.

Specific Canadian Features

  • The Peterborough Drumlin Field contains >2000 drumlins, the largest in central Canada.

  • Formation of the Oak Ridges Moraine post-Ice Age has geological significance in Ontario.

Shorelines and National Features

  • Glacial Lake Iroquois: Old shorelines of this ancient lake marked by physical features like the Scarborough Bluffs.

  • Erosion of the Canadian Shield impacts surrounding regions and contributes to sediment deposition.

Implications of Melting Glaciers

  • Antarctic Ice Sheet: Melting drives a positive feedback loop affecting global temperatures and water levels.

  • Global Concerns: More than 1/6 of the global population relies on glacier-fed rivers for freshwater; melting glaciers threaten this supply.