Topic 2 - Glaciation: EQ2 Flashcards
What is the accumulation zone?
Where there is a net gain of ice over the course of a year. Here, inputs exceed outputs
What is the ablation zone?
Where there is a net loss of ice during a year. Here, outputs exceed inputs
When is ablation at its highest?
During the summer (due to rapid melting of the ice)
When is accumulation at its highest?
During the winter (high amounts of snowfall and limited melting)
What is mass balance?
The year-to-year change between accumulation and ablation
What happens when accumulation exceeds ablation?
A positive mass balance occurs, the glacier’s mass increased and it advances
What happens when ablation exceeds accumulation?
A negative mass balance occurs, the glacier’s mass decreases and it retreats
What are the inputs in a glacial system?
Precipitation
Avalanches
Wind Deposition
What are the outputs in a glacial system?
Sublimation
Calving
Water
What is dynamic equilibrium?
The boundary between the accumulation zone and the ablation zone
What are the flows/transfers in a glacial system?
Evaporation
Sublimation
Meltwater Flow
Internal deformation
Basal Sliding
What are negative feedback loops?
Negative feedback loops regulate systems to establish balance and equilibrium
What is an example of a negative feedback loop?
The presence of ice decreases the albedo effect
When the temperature increases, ice melts and this increases the albedo and lowers the temperature, refreshing the water back into ice
What is an example of a positive feedback loop?
The Albedo affect
Snow reflects the sun’s rays, reducing ground temperature, leading to a decrease in temperature
What processes can a warm-based glacier move by?
Basal slip
Internal deformation
What processes can a cold-based glacier move by?
Internal Deformation only
What is Basal slip?
When the base of the glacier is at PMP, and meltwater present (lubricant) allows the glacier to slide at a quicker pace over the bedrock
What is internal deformation?
When the weight of the glacier ice and gravity causes the ice crystals to deform, so that the glacier moves downslope very slowly
What are the 3 types of basal slip?
Enhanced basal creep and regelation creep
Extensional and compressional flow
Surges
What is enhanced basal creep?
Whereby basal ice deforms around irregularities on the underlying bedrock surface
Objects are greater than 1m
What is regelation creep?
Basal ice deforms under pressure when encountering obstructions such as rock steps.
As the pressure increases, the ice reforms in a plastic state as a result of PMP.
Once it’s flowed over the obstruction, the pressure is lowered and the meltwater refreezes
What is extensional flow?
Over steep slopes, the rate of basal slip will increase and the ice will accelerate and thin
What is compressional flow?
Over shallower slopes, basal slip slows and the ice decelerates and thickens
What are Surges?
Short-lived events where a glacier can advance substantially, moving up to 100times faster than normal.
One cause are volcanic eruptions (especially in iceland) where the glacier turns into a toothpaste-like substance and can move 300-400m
What are the 2 types of internal deformation?
Intra-granular flow
Internal-granular flow
What is intra-granular flow?
Individual ice crystals fracture or deform due to the intense stresses within the ice. The mass of the ice will gradually deform and move downhill
What is inter-granular flow?
Individual ice crystals will slip and slide over each other, causing the mass of the ice to deform
What factors control the rate of movement?
Altitude
Slope
Lithology
Precipitation
Ice temperature
How does lithology affect the rate of movement?
If a glacier sits on permeable rock, some of the meltwater created by PMP will percolate through the rocks. This means that it won’t be kept in a glacial system and a decrease in meltwater and glacial movement
How does slope affect the rate of flow?
If a glacier sits in a steeper gradient, the rate of movement will increase due to more gravitational force
How does rates of ablation affect the rate of movement?
The more meltwater there is, the faster the movement as basal slippage increases
How does precipitation affect the rate of movement?
Higher snowfall leads to greater accumulation and faster movement
How does ice temperature affect the rate of movement?
In some environments, ice is so cold that it’s frozen to the bedrock which means that it will move much more slowly
How does altitude affect the rate of movement?
The greater the precipitation and lower the temperature, the greater the chance of supply of snow and ice, and an increase sim mass balance
What are the 4 types of crevasse?
Transverse crevasse
Longitudinal crevasse
Radial crevasse
Marginal crevasse
What is a transverse crevasse?
Cut across the glacier at approximately 90 degree angles
What is a longitudinal crevasse?
Oriented parallel to the flow direction of the ice
What is a radial crevasse?
Form in a splayed pattern at the snout of the glacier
What is a marginal crevasse?
Form near sides of glaciers
