Subglacial Monitoring Flashcards
What is being spoken about in subglacial properties?
Nature of the bed
Extent of subglacial deformation
Investigate the viscous/plastic debate
What does viscous mean?
Deformation is proportional to applied stress
The more you apply stress the more deforming
What does plastic mean?
Deformation negligible up to a critical stress- the yield stress- then immediate release
You can apply stress to a material but nothing will happen until you pass a yield stress and then it will fail
What kind of behaviour is viscous?
You can have a thick deforming bed (>10cm)
Ductile deformation- things flow not shear
What kind of behaviour is plastic?
You have a thin (1-2 cm) or no deforming layer instead basal sliding
Brittle deformation- something will snap
What methods can you use to see what’s going on subglacially?
Indirect
- geophysical techniques
Direct - margin - bed via hot water drill \+ Borehole video \+ Sampling \+ In situ measurements
What is ground penetrating radar?
An indirect geophysical technique
Great for ice thickness and other subglacial features, such as water channels and the nature of the bed
What is the basal reflection power?
Measures the strength of the reflection
What is seismic?
An explosion on the surface of the glacier which goes down to the bed and back up and you pick up the speed of the return.
E.g using a sledgehammer or sending an explosive signal down a borehole.
What are margin studies?
Measure velocity of debris rich basal ice in marginal positions.
- Strain gauges
- EDM
Not looking underneath the glacier really but still gives you a good idea.
What are direct investigations of the glacier bed by hot water drill?
A giant car wash that takes water from the surface of the glacier, heats it up, squirting down the glacier making a hole with the heat.
Relatively easy
Examine
- Borehole itself (ice properties)
- Water (englacial/subglacial)
- Bed
What’s the issue with till sampling?
Getting it undisturbed
What are some aims of in-situ process studies?
Finding out till thickness, till strength, till velocity
What is a ploughmeter?
Measure sediment strength
Dropped through into the sediment, dragged through- if weak not much pressure, if strong lots of pressure
What is a drag spool?
Measures the amount of deformation/ sliding
Put an anchor in the till using a heavy weight
The anchor remains stationary, the ice moves over and drags out a connected spool, measure the electrical change
