Glaciers: Movement Flashcards
What is internal deformation?
occurs when ice crystals orientate themselves in the direction of the glaciers movement and slide past each other (contributes 1-2cm per day). The deformation of layers of ice or individual ice crystals caused by the pressure of the weight of the ice. Causes some layers to move faster than others, so different parts of the glacier can be faster. As surface ice moves faster, crevasses develop. If the glaciers flows just by internal deformation, then the rate of creep decreases with depth, with fastest ice movement at the surface and slowest (or no) ice movement at the base and sides.
What is basal sliding?
the sliding of a glacier over bedrock, a process usually facilitated by the lubricating effect of meltwater - in warm based glaciers. Meltwater at the base due to overlying pressure of ice and geothermal heat from below. Pressure melting allows the ice to move over obstacles (as increase pressure occurred when meets) and refreezing occurs once the obstacle is overcome. This melting and refreezing is called regelation.
What is compressional flow?
when ice hits a shallow gradient, friction causes the ice to slow down, build up and compress. This causes the ice to get thicker.
What is extensional flow?
when ice meets a steep downhill gradient (usually going over a hill), gravity forces the ice to increase in velocity. Friction causes the ice to thin out and extend, causing deep cracks called crevasses.
What is rotational slip/flow?
compressed ice becomes trapped in a hollow, but gravity causes it to continue to move downwards. Meltwater assists in moving the glacier in a rotational movement, causing it to continually erode the hollow
