Glacial Erosion: Processes
The wearing away of the landscape by glaciers is called Glacial erosion. In the UK, the results of glacial erosion during the last ice age can be seen in many of the upland areas such as north Wales, highland Scotland and the Lake District.
There are three main processes that cause glacial erosion. These processes may work together or on their own, depending on conditions at the time:
Freeze-thaw can only work where day time temperatures allow water to melt, and it is cold enough at night for the water to freeze again. It works on cracks, weaknesses and hollows in rock. It goes like this...
Plucking happens when rocks and stones around the glacier become frozen to the base or sides of the ice. They are then attached to the ground (that doesnt move) and the glacier (which is moving). One of two things will happen; EITHER the rock is so strongly attached to the ground that the ice breaks off it as the glacier moves, OR the ice pulls or plucks the rock out of the ground. When the ice wins, plucking has occurred.
Abrasion is wearing something down by rubbing it against something else. Glasspaper and kitchen scouring pads work by abrasion.
In glaciers abrasion occurs then rocks and stones are picked up by the glacier (by plucking or from moraine that falls onto the surface of the glacier and works its way down to the bottom), and are rubbed against the bedrock at the bottom and side of the glacier as it moves. This turns the ice from a smooth surface into something like a gigantic scouring pad. As the glacier moves the rocks scour the bedrock and erode it away. Scratch marks, or striations, show where rocks have been scraped over the surface.
Photo of a section of rock once covered by a glacier that eroded by abrasion. You can see the flattened surface left behind, and the striations (scratches) created as chunks of rock were dragged over it by the glacier