Surging Exam Flashcards
What are surges?
(Meier and Post, 1969)
Surges are a dramatic glacier advance
They have a long quiescent phase of normal velocity…and then a short surge phase glacier 10-10,000 x faster
Period (10-100 years)
Only 1% of glaciers on the globe
What is the morphology of a surge?
(Jiskoot et al., 2010)
They have a wave like bulge because the top part of the glacier is flowing so much faster than the lower part of the glacier.
How can we tell if a glacier has surged or not?
(Sharp, 1988)
Amalgamation of features…
Large push moraines
Folded medial moraines
Lateral moraines
Concertina eskers
Hummocky outwash areas
Rigid bed model
(Kamb et al., 1985)
This is because there is a build up of high water pressure in the basal water system.
This leads to increased basal sliding- these cavities become linked and the surge front advances as it destroys the tunnel system, and the higher water pressure makes the cavities.
Deforming bed model
(Clark et al., 1984)
The front of the glacier is frozen and the rest is warm based- the surge bulge forms at this boundary.
The subglacial water is flowing through the till
There is a barrier to sliding (frozen toe) stopping the water flowing through the till.
Water pressure builds up and suddenly passes through threshold and glacier shoots forward.
Pressure melting point model
(Murray et al., 2003)
At the start of the cycle, the glacier is cold based (polythermal).
Ice builds up in surge front causing thickening until pmp is reached in part of the glacier- turned into warmbased.
Basal meltwater is produced, which leads to high pore water pressures and weakening of the till.
Accelerated deformation of the till produces frictional heating, more melting, sliding
This causes the ice to thin, causing refreezing and the surge ends.
Glacier velocity is never constant…but it can be divided into two types.
Continuous
Discontinuous
What is a continuous glacier?
One which is travelling at a similar speed most of the time.
Slow- cold based glacier- <30 m/a
Fast- warm based glacier- 50-100 m/a
What is a discontinuous glacier?
Discontinuous- change their speed dramatically
Surging glaciers >10,000 m/a
Ice streams >400 m/a
What are short term speed up events?
These are usually melt water driven but sometimes tidal driven.
Often called stick slip motion- small thing that happens everyday- Tidal modulated twice per day.
Englacial water storage model
(Lingle and Fatland, 2003)
Water is stored englacially, these can be observed as ‘bulls eye zones’ using INSAE observation, if this large storage all goes to the bed at once = glacial surge.
