Lecture 2 Flashcards
(31 cards)
What is an ice sheet?
A mass of glacier ice that covers a land area greater than 50 000 km2
What is the largest Ice mass on Earth today?
The Antarctic Ice Sheet.
How much of the Antarcitic continent does the Antarctic Ice Sheet cover?
98%
What is the total ice volume of the Antarctic Ice Sheet?
58 m sea level equivalent
West A. 5 m
East A. 53 m
How much of the fresh water on Earth does the Antarctic Ice Sheet contain?
61%
Why is the Antarctic Ice Sheet mass more or less constant?
Because the mass loss from the West has been compensated by the mass gain of the East
Acculmulation on glaciers?
Precipitation, rain, hail, freezing rain, snow, wind-blown snow, avalanching, hoar frost
Surface ablation/output of glaciers?
Outputs such as wind-blown snow, avalanching, sublimation, surface-meltwater-runoff, subaerial melt, sublimation, calving, subaqueous frontal melt (meltwater, icebergs)
What is the surface mass balance of a glacier?
Accumulation minus Surface ablation
What is the mean ice thickness of the Antarctic Ice Sheet?
2 km
What is the maximum thickness of the grounded ice on the Antarctic Ice Sheet?
5 km
What is the grounding line?
It is the boundary between grounded and floating ice sectors
How much mass has the Antarctic Ice Sheet lost?
Less than 1%
Major players: ocean (mass loss) and precipitation (mass gain)
What causes the mass loss of the Antarctic Ice Sheet?
49 percent due to ice calving
50 percent due to melting under ice shelves
<0,5 percent due to subglacial melting under grounded ice sectors
What is ice flow
The flow of ice sheets through deformation and sliding, which removes the ice from grounded sectors and into the ocean
Where does the ice on an ice sheet flow the slowest?
On the thickest parts
Where does the ice on an ice sheet flow the fastest?
On the ice shelves and the edges where rapidly flowing ice streams and outlet glaciers develop
Where does ice sliding occur?
where the ice
1 melts at the base,
2 sits on top of hydrological systems or
3 is underlain by saturated, deformable sediment
What causes ice flow on the Antarctic ice sheet?
Pressure melting point: Basal ice of ice sheets melts at negative temperatures due to the pressure of the overlying layers.
Geothermal heat warms the base of ice sheets and makes the ice base deform and melt.
Geothermal heat
the heat rising from the deep Earth interior
Topographically constrained flow
When basal sliding occurs, ice erodes subglacial bedrock through plucking and abrasion which forces rapid ice flow, and the locations of ice streams = facilitates further erosion
Sub-shelf melting
Warm ocean currents penetrate under ice shelves and melt from below.
How does ice calving occur?
Weakness and formation of cracks
combined with surface melt promote crack penetration, resulting in a break-off of a part of an ice shelf
Second largest ice mass
The Greenland Ice Sheet
