Past & Present Ice Cover (Edexcel A Level Geography)

• The cryosphere is all the frozen regions on Earth and covers 13% of the planet's surface
• The term comes from the Greek word 'kryo', meaning cold
• Ice can be found in
  • High latitudes - Arctic and Antarctic Circles of more than 65° north and south of the equator
  • High altitudes - found in mountain ranges, which can be at any latitude (Drakensberg Mountains, SA is over 3000m high at a latitude of 29° south of the equator)
• Features of the cryosphere include: 
  • Snow
  • Ice (69% of the world's freshwater is stored as ice)
  • Permafrost and frozen ground - not all frozen ground is permafrost
  • Glaciers
  • Ice caps, sheets and shelves
  • Icebergs
  • Sea, river and lake ice

Parts of the cryosphere

• Most of the cryosphere is found in Antarctica (85%) and the Arctic polar region (12%), as ice sheets, shelf ice, and permafrost
  • The largest, single ice mass on Earth is the Antarctic ice sheet, covering 8.3% of the global land surface 
  •  It took millions of years to form; is up to 4.8 km (3 mi) deep in parts; and covers approx. 14 million km² (5.4 million mi²) and contains 30 million km³ of ice
  • If it melted, it could raise sea levels by 58 meters (190 feet) 
• Permafrost areas are significant global carbon stores and help regulate levels of carbon in the atmosphere
• The cryosphere helps regulate Earth’s climate through its high surface albedo effect
• As the climate warms, the cryosphere also changes through feedback mechanisms, which further influences the climate:
  • Increased snow and ice melt, exposes more dark surfaces to insolation
  • Which increases surface absorption of solar radiation, causing further melting and release of stored carbon and methane into the atmosphere, which leads to further atmospheric warming
  • This is a positive feedback loop, which exacerbates the impacts of climate change

• There are two groups of ice masses:
  • Constrained - these do not have a dome-like structure, so the flow and shape of the ice is influenced by its surroundings - valley, piedmont and cirque glaciers
  • Unconstrained - the flow and shape of this ice is not influenced by its surroundings - ice sheets, shelves and caps
    • These have the basic shape of a broad, slowly moving, central dome, with channels of faster-moving ice that flows to, and at, its margins

Unconstrained 

• 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 landmass
  • 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 

• Ice fields
  • Ice that covers a mountain plateau, but does not extend the high-altitude area
  • Not thick enough to bury the topography and covers 5 -1500km³ 
  • Examples include the Himalayas, Rockies, Andes, and the Southern Alps of New Zealand 
• 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 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

Thermal regime of ice masses

• This refers to an ice mass's basal temperature and indicates whether water or ice will be present

Pressure melting point (pmp)

• The temperature at which ice melts at a given pressure is the pressure melting point (pmp)
• The melting point of water depends on air pressure above the ice
• As air pressure increases, the temperature at which ice melts lowers
• At 1 atmosphere pressure, the melting point of ice is 0°C
• At 200 atmospheres, the melting point decreases to -1.85°C

Warm-based glaciers

• Occur in temperate regions such as southern Iceland and western Norway
• They are relatively small and range in width from hundreds of meters to a few kilometres
• Melting occurs during the summer months
• It is this meltwater that 'lubricates' the base and sides of the glacier, which assists movement (called basal sliding) and increases rates of erosion, transportation and deposition
• As such, all ice in these glaciers is at, or close to, the melting point of ice
• Temperatures at the base are, therefore, at or just above the pressure melting point

Cold-based glaciers

• Occur in polar regions such as central Greenland and Antarctica
• They are large, vast sheets and caps of ice covering hundreds of km²
• Temperatures remain below melting point, with low rates of precipitation, resulting in low levels of accumulation 
• Basal temperatures remain below the pmp, therefore, basal sliding does not happen
• This results in little erosion, transportation and deposition
• Any movement is by internal deformation
  • The ice stays frozen to the bedrock and moves slowly at 1-2cm a day
  • Orientation of the ice crystals in the glacier, to the direction of movement, allows the crystals to slide over each other

Polythermal glaciers

• These are glaciers with both warm and cold bases but at different altitudes
• They usually show a cold base in their upper reaches (high altitudes)
• At the lower altitudes, their bases are warm with meltwater

Past glaciation

• The last glacial maximum was 21,000 years BP, where over 30% of the Earth's surface was glaciated
• The polar ice sheets covered much of the UK and major parts of southern Europe were periglacial
• Sea levels dropped, and shorelines extended farther out, creating more land (water was trapped in ice sheets)
• The climate was drier, because most of the water on Earth's surface was ice, resulting in less precipitation
• Earth's average temperature was 6°C (average now is 14-15°C)

Extent of global ice during the Pleistocene epoch

• The present-day distribution of cold environments can be divided into polar, glacial, alpine and periglacial areas
• Polar - considered areas of permanent ice within the northern and southern extremes of the Antarctic and Arctic regions
• They are found in areas of high latitude, with long winters and short summers, with high levels of storms and cold winds
  
  • The Arctic polar environment can be defined either by the Arctic circle at 66° N or by the July isotherm of 10° C
    • Isotherms are areas of the same temperature
    • July is the hottest month and areas north of this line have an average of 10°C or below
    • Winter sea ice is shrinking
  • The Antarctic is much colder than the Arctic, with strong westerly winds, cold oceans and a large landmass
  • Winter sea ice is increasing 
  • Defined by the 10°C January isotherm (January is the hottest month in the southern hemisphere)
• Other examples include Greenland and northern Canada

Distribution of present day cold environments

• Glaciated landscapes vary, dependent on location - polar, glacial, periglacial and alpine
• Glaciated landscapes can be divided into active (current) or relict (past) landscapes
• Geology influences the nature of a glaciated landscape
  • Igneous rock is harder to erode and often makes up 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 flows 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
    • The Highlands of Scotland, the Lake District and Snowdonia (Eryri), North Wales show many relict landscapes from the Pleistocene epoch, including arêtes, erratics, cirques/corries, and corrie lakes
  • Sedimentary and metamorphic rocks are found mainly in low-lying areas (already eroded from the uplands) and are easier to erode
    
    • During the last Ice Age, the advancing ice sheet moved chalk, boulder clay etc. into the south and east of England 

The extent of the UK's glaciation during the last Ice Age