Plucking, in the sense relating to glaciers, is when a glacier erodes away chunks of bedrock to be later deposited as erratics. Glacial plucking exploits pre-existing fractures in bedrock made before the glacier arrives. When the ice comes into contact with a joint, the friction of the ice caused through resistance results in some of the ice to melt. This plays a key role in opening and creating new fractures but has only provided small segments of loose material. This is then followed by the entrainment of the loosened rock by the ice. The process of entrainment process refers to loose rock material being frozen onto the base of the glacier and therefore being incorporated into the glacier ice. Plucking may also be known as quarrying. Aletsch glacier, Switzerland A glacier is a large, long-lasting river of ice that is formed on land and moves in response to gravity. ... An erratic is a fragment of glacial till carried by ice, sometimes for hundreds of miles, and deposited on rocks of a different geologic composition. ...

References

• David Anderson, Glacial and Periglacial Environments (Access to Geography S.) (Hodder Education, 2004) A comprehensive A-Level Geography textbook to the subject through such topics as distribution, formation, landscapes, processes and effects on the physical environment...