Cryosphere Flashcards
What is the Equilibrium Line Altitude
The line where accumulation equals ablation; accumulation generally happens higher on the glacier and lower there is more ablation.
What is the Mass Balance of a glacier
Mass Balance = Surface Mass Balance (accumulation - ablation) - Discharge (icebergs etc.)
What is Rheology and the Constitutive Relation?
Rheology of a material is the properties related to its flow. The constitutive relation refers to the relationship between stress and strain.
How does the constitutive relationship vary?
For elastic materials, strain is proportional to stress.
For plastic materials, the strain rate is 0 until a critical yield stress.
For viscous material, the strain rate is nonlinearly proportional to stress. Some index n of stress is proportional to the derivative of strain. For Newtonian viscous materials, n=1; for ice n=3
How does basal sliding work?
Must have water to lubricate - this can come through crevasses, hydrofractures (draining lakes) etc.
Subglacial water pressure allows quicker basal sliding as cavities grow.
What is the Grounding Line?
The grounding line is where the ice last contacts the bed. Past this, it either becomes a shelf or calves as icebergs. It also begins to contribute to global sea level.
Ice flux across the grounding line is non-linearly proportional to ice sheet thickness at the grounding line:
What is the Marine Ice Sheet Instability?
a positive feedback loop with retreat.
If the bed topography is sloping towards the interior, the ground line retreats, the grounding line thickness increases, seaward ice flux increases which then causes further retreat.
What is BUTTRESSING?
Buttressing is when features on the sea floor or lateral boundaries past the grounding line interrupt the shelf. These provide significant drag, and so a resistive stress that opposes the ice flow.
Glaciers accelerate if the ice-shelf thins due to loss of this resistive buttressing.
How can past ice sheets be mapped?
Looking at isostatic rebound and glacial features like moraines, lineations, erratics and eskers.
What influences long-term glacial growth?
periods of weak summer insolation, caused by:
- Precession - how rotation of the Earth tilts
- Eccentricity - how elliptical the orbit is
- Obliquity - how tilted the Earth is
What is SEA SURFACE HEIGHT
Distance from sea surface to ellipsoid
What is RELATIVE SEA LEVEL
Distance from sea surface to crustal height
What is DYNAMIC TOPOGRAPHY
Distance from sea surface to geoid.
