Plucking (glaciation)

Plucking, also referred to as quarrying, is a glacial phenomenon that is responsible for the erosion and transportation of bedrock, especially large "joint blocks". This occurs in a type of glacier called a "valley glacier". As a glacier moves down a valley, friction causes the basal ice of the glacier to melt and infiltrate joints (cracks) in the bedrock. 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. This produces large pieces of rock called joint blocks. Eventually these joint blocks come loose and become trapped in the glacier.

In this way, plucking has been linked to regelation. Rocks of all sizes can become trapped in the bottom of the glacier. Joint blocks up to three meters have been "plucked" and transported. These entrained rock fragments can also cause abrasion along the subsequent bedrock and walls. Plucking also leads to chatter marks, wedge shaped indentations left on the bedrock or other rock surfaces. Glacial plucking both exploits pre-existing fractures in the bedrock and requires continued fracturing to maintain the cycle of erosion. 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 period

A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate between glacial periods. The last glacial period ended about 15,000 years ago. The Holocene epoch is the current interglacial. A time when there are no glaciers on Earth is considered a greenhouse climate state.

Quaternary ice age

Within the Quaternary glaciation (2.58 Ma to present), there have been a number of glacials and interglacials.

Last glacial period

The last glacial period was the most recent glacial period within the current ice age, occurring in the Pleistocene epoch, which began about 110,000 years ago and ended about 15,000 years ago. The glaciations that occurred during this glacial period covered many areas of the Northern Hemisphere and have different names, depending on their geographic distributions: Wisconsin (in North America), Devensian (in Great Britain), Midlandian (in Ireland), Würm (in the Alps), Weichsel (in northern central Europe), and Llanquihue in Chile. The glacial advance reached its maximum extent about 18,000 BP. In Europe, the ice sheet reached northern Germany.