Glacial Systems (AQA AS Geography): Revision Note

Systems Approach to Glaciers

• Glaciers are defined as:

• Glaciers are open systems with inputs and outputs to external systems, including fluvial and atmospheric systems

• There are flows of energy, ice, water and sediments between stores

Inputs

• Kinetic energy from wind and moving glacier

• Thermal energy from the Sun

• Geothermal energy from the Earth

• Rock debris from weathering and transportation

• Atmospheric inputs from:

  • Snow from precipitation, avalanche or blown-in

  • Condensation of water vapour

  • Sublimation of vapour directly to ice crystals

Outputs

• Energy through evaporation and sublimation

• Water vapour through sublimation of ice and snow 

• Meltwater

• Icebergs and ice blocks

• Glacial and fluvio-glacial sediments

• Snow is blown away

Stores

• Accumulated debris from weathering, erosional and depositional processes

• Ice from the glacier itself

• Meltwater is stored on and within the glacier (supraglacial lakes are on top of a glacier)

• Potential energy stored from movement of glacier

Flows

• Debris flow through glaciers from surface storage to landforms

• Kinetic energy from movement of glacier

• Meltwater flow

• Glacial movement/flow through gravity

• A glacial system has positive and negative feedback loops to keep it in dynamic equilibrium

  • E.g., sediment on the glacier absorbs insolation and begins heating

  • This leads to the melting of the ice 

  • Exposing more sediment and increasing the rate of insolation absorption 

  • This is a positive feedback loop 

• Output through ablation (melting) is balanced by glacial input of accumulation (usually snow)

• Equilibrium of the glacier is maintained when input and output are balanced – neither a gain nor loss of ice and the glacier remains the same size

• All these factors combined, create the distinctive glacial landscape, that is made from a range of erosional and depositional landforms

Characteristics of Glacial Landscapes

• The glacial system are the processes of erosion, deposition and flow of material (ice, water and debris) across the Earth's surface

• These processes produce erosional and depositional features that, overall, produce the glacial landscape

• A glaciated landscape has distinctive characteristics that include:

  • Glaciers

  • Sharp mountain peaks 

  • Steep mountainsides and upper lakes

  • Deep U-shaped valleys or troughs

  • Features of deposition and erosion, such as striations left behind on rocks, tell the direction of ice travel

  • Outwash plains and braided rivers, etc. 

• Glaciated landscapes can be divided into an active (current) or relict (past) landscapes

• Glaciated landscapes vary, dependent on location – polar, glacial, periglacial and alpine

• Geology influences the nature of a glaciated landscape

  • Igneous rock is harder to erode and often make up the high mountains with steep sides and hollows
    

    • Large amounts of poorly sorted sand, gravel, and boulders are plucked and pried from the surface and mountains

    • As the glacier flow over bedrock, the sediments trapped in the ice, are ground into a fine powder called rock flour

    • Rock flour acts as sandpaper, that polishes the surface of exposed rock to a smooth finish called glacial polish

    • Larger rock pieces scrape over the surface, creating grooves called glacial striations

  • Sedimentary and metamorphic rocks are found mainly in low-lying areas (already eroded from the uplands) and easier to erode
    

    • During the last Ice Age, the advancing ice sheet moved chalk, boulder clay, etc. into the south and east of England 

Types of glaciers

• There are two groups of glaciers:

  • Constrained are glaciers that do not have a dome-like structure, so the flow and shape of the glacier is influenced by its surroundings, such as valley, piedmont and cirque glaciers

  • Unconstrained are glaciers that remain unaffected by their surroundings, such as ice sheets, shelves, and caps

    • They all have the basic shape of a broad, slowly moving, central dome, with channels of faster-moving ice that flow to its margins

Unconstrained 

• Continental glaciers or ice sheets

  • Continuous masses of ice, that cover areas greater than 50,000 km³ 

  • With no surrounding mountains or features to contain them, continental glaciers spread out and cover the surface

  • They spread out from the centre and can cover whole valleys, plains and mountain ranges with ice

  • Sometimes only the tips of mountain peaks show above the ice, called nunataks

  • In 2009, Antarctic scientists found a mountain range, as large as the European Alps, hidden under 2.5 miles (4 km) of ice 

• Ice caps

  • Cover areas of less than 50,000km³

  • Usually centred on a mountain's high point (called a massif), the ice flows flow in multiple directions to form a cap

  • This flow of ice feeds into a series of glaciers at its edges

  • Polar ice caps are not strictly 'caps', as they are greater than 50,000 km³

• Ice shelves

  • These are thick, floating slabs of ice, permanently attached to a land mass

  • Found where ice flows down to the coast and out onto the ocean's surface

  • Only found in Greenland, Northern Canada, Antarctica and the Russian Arctic

Constrained 

• Piedmont glaciers

  • Found at the foot of mountains, where a mass of ice has flowed downslope and fans out, forming lobes of continuous ice

• Valley glacier

  • Ice is surrounded by high mountains and fills the valley

  • They are usually ribbon-shaped and vary in length from a few kilometres to over 100km 

  • They can be a single feature or made up of multiple glacial tributaries from surrounding valleys

  • Most begin as mountain glaciers and spread/flow to gorges, basins and across the valley floor

  • Examples include the Andes, Himalayas and European Alps

• Cirque glaciers

  • The most common type of glacier is found in nearly all areas where snow and ice accumulate – e.g., alpine regions

  • Confined to either the upper parts of a glacial trough or within the hollowed, cirque basin itself

  • It is the basin that dictates the size, shape and flow of the glacier

  • Niche glaciers are smaller versions of cirque glaciers