![]() Plucking of bedrock also occurs in steep upland rivers, and shares a number of similarities with glacial examples. Glacial plucking is most significant where the rock surface is well jointed or fractured or where it contains exposed bed planes, as this allows meltwater and clasts to penetrate more easily. Glacial plucking both exploits pre-existing fractures in the bedrock and requires continued fracturing to maintain the cycle of erosion. Plucking also leads to chatter marks, wedge shaped indentations left on the bedrock or other rock surfaces. These entrained rock fragments can also cause abrasion along the subsequent bedrock and walls. Joint blocks up to three meters have been "plucked" and transported. Rocks of all sizes can become trapped in the bottom of the glacier. In this way, plucking has been linked to regelation. Eventually these joint blocks come loose and become trapped in the glacier. This produces large pieces of rock called joint blocks. The freezing and thawing action of the ice enlarges, widens, or causes further cracks in the bedrock as it changes volume across the ice/water phase transition (a form of hydraulic wedging), gradually loosening the rock between the joints. As a glacier moves down a valley, friction causes the basal ice of the glacier to melt and infiltrate joints (cracks) in the bedrock. ![]() This occurs in a type of glacier called a "valley glacier". Plucking, also referred to as quarrying, is a glacial phenomenon that is responsible for the weathering and erosion of pieces of bedrock, especially large "joint blocks". Glacial erosion of bedrock Zone of plucking in the formation of tarns and cirques Glacially-plucked granitic bedrock near Mariehamn, Ă…land ![]()
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