CHAPTER 9: GLACIAL PROCESSES, PATTERNS AND LANDFORMS
Over time, after a greatweight of ice has accumulated (about 30 m), so much air has been removed by compression that the ice turns hard and blue. It takes 30–40 years for snow to form this dense glacier ice. Blue glacier ice is so hard that when armed with embedded rock fragments, it can bulldoze through rock and soil, completely reshaping the landscape. Whether a glaciermoves forward or retreats back up
the valley depends on the balance between accumulation and melting. If more snow is added than is lost through melting, the glacier will move forward.
Fig. 4 Blue glacier ice 9.3 How glaciers move
Ice moves downhill because of the force of gravity upon the ice. The movement of glaciers involves the processes of:
Crevasse zone – ice splits as it moves over steep slope on leaving its corrie
Plastic flow in body of ice
Plastic flow in body of ice
Basal flow Rock outcrop
Plastic flow Plastic flow
Basal flow Basal flow Fig. 5 The movement of glaciers 1. Sliding (basal flow)
The greatweight of ice and pressure at its basewill cause it tomeltwhich allows the ice to slide along the valley floor and sides. The same effect is used in ice skating.
2. Plastic flow If the glaciermeets a large object in its path, such as a rock outcrop, icewillmelt close to the object because of the increased pressure. This creates meltwater which allows the glacier to mould its way over and around the object.
3. Rotational slip
Ice can also move when the ice slips around a central point, much like a child on a slide when they reach the bottom of the steep bit. Rotational slip is very important in the creation of corries.
The longest glacier in the world is in Antarctica. It is the Lambert-Fisher Glacier and is over 700 km long and 64 km wide.