Glacial Systems (AQA A Level Geography)

• Glaciers are defined as:

Large rivers (mass) of ice, moving downhill, under the influence of gravity

• 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

Glacial System

Diagram showing the features of an open glacial system

• 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

• 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 - 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 rock 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 - these do not have a dome-like structure, so the flow and shape of the glacier is influenced by its surrounding - valley, piedmont and cirque glaciers
  • Unconstrained - the flow and shape of these glaciers are not influenced by its surroundings - 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 (4km) 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 50,000km³
• 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
  • Most common type of glacier and found in nearly all areas where snow and ice accumulates - 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