Glacial Processes and Landforms Flashcards
How much of the world’s freshwater is stored in the global cryosphere?
- 75 percent
- Short time scales in snow, rivers and lake ice, sea ice
- Short and long time scales in glaciers and ice caps, frozen ground
- Short to long timescales in ice sheet margins to ice shelves to ice sheets
How much would global sea level rise if all of the ice in Antarctica melted? Greenland?
- Antarctica: 58m
- Greenland: 7m
Thermal expansion and mountain glacier melt (not greenland/antarctica) explain how much of the observed sea level rise since 1971?
- 75 percent
- Thermal expansion will be the biggest contributor to SLR, followed by mountain glacier melt
Percent of global land surface from most to least for ice on land
- Seasonally frozen ground 33
- Terrestrial permafrost 9-12
- Antarctica 8.3
- Greenland 1.2
- Northern hemisphere freshwater (lake/river) ice 1.1
- Glaciers 0.5
- Snow cover 1.3-30.6 (highly variable
In all climate change scenarios, what is the largest contributor to SLR projections? Which one gets the press?
- Thermal expansion is largest contributor
- But melting glaciers gets all the press b/c is more visually spectacular even though it only comes in second
Glacier size and reaction times
- Ice sheets, 1000m thick, 100km long, reaction time 1000yrs
- Valley glaciers, 100m thick, 10km long, 100yr reaction time
- Cirque glaciers, 10m thick, 0.1km long, 10yr reaction time
What are the 2 criteria for a glacier?
- Perennial accumulation of snow and ice
- Flows under it’s own weight
How are glaciers classified by?
- Morphology (size)
- Flow dynamics
- Thermal properties
Snow to ice density
- Increases in density w/ depth in glacier
- Fluffy snow 0.05-0.2 g/cm3
- Firn 0.4-0.8 g/cm3
- Glacial ice 0.8-0.9 g/cm3
- Pure ice 0.917 g/cm3
Mass Balance, Bm
- Glacier’s chequebook
- Balance btwn inputs/accumulation and outputs/ablation of snow, ice, water and vapour
- Most of world’s glaciers are negative, but only few are monitored
- If Bm > 0, glacier grows, advances terminus
- If Bm <0, glacier shrinks, terminus retreats
How many glaciers are there worldwide?
- 170,000
- Even in Africa on Mt Kiliminjaro (16 ice fields) and 2 other Mnts
How is the Mass Balance accounted for?
- Whole year gives balance, mean water equivalent
- Can’t look at just summer b/c negative or winter b/c positive
Equilibrium line altitude (ELA)
- Elevation where no net gains or losses of water occurs
- Connected to local climate (change)
- Same as firn line in late summer/early fall
- Controlled by temp and precip
Thermal classification of glaciers
- Ice temp important to control flow
- Polar/cold glaciers
- Temperate/warm glaciers
- Subpolar/polythermal glaciers
Pressure melting point, PMP
- Water melts/freezes at 0C at 1 atm pressure
- But PMP decreases w/ increasing pressure
- i.e. Melts at a lower temperature than 0C at higher pressure
- Declines by 1C for every 14MPa
- ex. 20MPa = PMP approx. -1.6C
Polar/cold glaciers
- Temp «_space;PMP
- Frozen to bed (at least at margins)
Temperate/warm glaciers
- Temp at approx. PMP throughout
- Water at bed
Subpolar/polythermal glaciers
- Parts of glacier at PMP temp and other parts not
- Most pleistocene ice sheets were polythermal
Continental size/morphology classification
- Ice sheet, > 50,000 km2 that buries landscape
- Ice cap, < 50,000 km2 that buries landscape
- Ice shelf, floating ice anchored to land mass
Transitional size/morphology classification
- Outlet glacier, bounded by ice-free ground at margins
- Ice stream, bounded by ice at margins
- Piedmont glacier, valley glacier that exits mountain onto flat ground
Alpine size/morphology classification
- Ice field, not domed like cap or shelf
- Valley glacier, ice flowing down valley
- Cirque glacier, ice occupying hollow in bedrock that it formed
- Niche glacier, ice occupying hollow in bedrock that it didn’t form
- Surge-type glacier, sub-category which move very rapidly for short periods of time
Pemberton icefield
300km2
Columbia icefield
325km2
Jakobshavn Isbrae, Greenland
- Outlet glacier fed by ice stream
- Flowing up to 15km/yr, in rapid retreat
- Fastest glacier in the world
- Accounts for approx. 4 percent of avg. 20th century rate of SLR
- Warmer conditions increase melt and lubrication at base, increase speed
- Warmer winders allow iceberg calving and high flow rates to continue
Glacier flow mechanisms
- Internal deformation
- Basal sliding, if warm based
- Subglacial bed deformation
- Top part of glacier is passive, not contributing to flow, goes along for the ride
