Surging

Question 1

What are the 2 surging mechanisms?

Answer 1

Hydrological switch - hard bed

Thermal switch - soft bed

Question 2

What is the hydrological switch?

Answer 2

Hard bed. High accumulation forms bulge and pinch point.
Glacier initially has discrete, efficient channels.
High deformation causes increased water pressure in channels, causing leakage. Efficient to inefficient. Water at base lifts glacier off bed causing surge. Positive feedback.
During summer, increased melt causes return to discrete, efficient channel.

Question 3

What is the thermal switch?

Answer 3

High accumulation causes bulge and pinch point to form. Increased pressure causes basal melt as pmp is reached. Water reaches the bed and thaws the frozen sediment at base. Glacier moves along on wet sediment.
Positive feedback - faster flow = frictional heating = more meltwater.

Question 4

Case Study for Hydrological switch?

Answer 4

Hard bed = Kamb (1985) or Clarke (1987).
Variegated Glacier, Alaska.

One of the only glaciers to have primary data on surging.
Post surge - multiple crevasses, thinner.

Question 5

Case Study for Thermal switch?

Answer 5

Soft bed = Clarke (1984)
Trapridge, Yukon.

Only slight increase in velocity when surged.

Quiescent phase = 10-100s years.
Active phase = 1-10 years.

Question 6

Other causes:

Answer 6

Landslides - add weight on the ice and cause ablation to shut off as it insulates glacier. But pressure increases pmp, water at base and then surges.

Case Study: frans josef, Waiho loop. (Tovar).

Mining:
Kyrgyzstan, 150m of debris dumped on glacier. Surged 1-3km.

Question 7

What is a surging glacier?

Answer 7

Multi-year oscillations between extended periods of normal motion and brief periods of fast motion (Raymond 1987).