Drumlin

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A drumlin – from the Gaelic word droimnín ("little ridge"), first recorded in 1833 – is an elongated whale-shaped hill formed by glacial ice acting on underlying unconsolidated till or ground moraine.

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Drumlin formation

Drumlins and drumlin clusters are glacial landforms which have been extensively studied. Geologists have proposed several theories about their origin. They are formed a short distance within the receding glacier ice and record the final direction of ice movement.[1] Drumlins occur in symmetric, spindle, parabolic, and transverse asymmetrical forms. Drumlins are commonly found with other major glacially-formed features and are related on a regional scale to these landforms. The large-scale patterns of these features exhibit spatial organisation of the drumlin-forming flows with related tunnel valleys, eskers, scours, and exposed bedrock erosion (scalloping and sichelwannen).[2]

Although one formation theory originally proposed since the 1980s by John Shaw and collaborators postulates drumlin creation by a catastrophic flooding release of highly pressurized water flowing underneath the glacial ice,[3] the recent retreat of a marginal outlet glacier of Hofsjökull in Iceland[4] provided the opportunity for direct study of a drumlin field with formation of >50 drumlins ranging from 90–320 m in length, 30–105 m in width, and 5–10 m in height. This, when combined with drumlin formation identified through imaging beneath the West Antarctica ice, resulted in a significant step in geomorphologic understanding. The Hofsjökull marginal drumlins formed through a progression of subglacial depositional and erosional processes with each horizontal till bed within the drumlin created by an individual surge of the glacier.[5] Erosion under the glacier in the immediate vicinity of the drumlin can be on the order of a meter's depth of sediment per year, with the eroded sediment forming a drumlin as it is repositioned and deposited.[6]

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