Drumlin

A drumlin, from the Irish word droimnín ("little ridge"), first recorded in 1833, in the classical sense is an elongated hill in the shape of an inverted spoon or half-buried egg[1][2] formed by glacial ice acting on underlying unconsolidated till or ground moraine.

They form near the margin of glacial systems, and within zones of fast flow deep within ice sheets, and are commonly found with other major glacially-formed features (including tunnel valleys, eskers, scours, and exposed bedrock erosion).

[13] This field surrounds the current lobe of the glacier and provide a view into the past, showing the previous extent and motion of the ice.

[citation needed] Drumlins may comprise layers of clay, silt, sand, gravel and boulders in various proportions; perhaps indicating that material was repeatedly added to a core, which may be of rock or glacial till.

Thus, accretion and erosion of soft sediment by processes of subglacial deformation do not present unifying theories for all drumlins—some are composed of residual bedrock.

[16] The first, constructional, suggests that they form as sediment is deposited from subglacial waterways laden with till including gravel, clay, silt, and sand.

This hypothesis requires huge, subglacial meltwater floods, each of which would raise sea level by tens of centimeters in a few weeks.

Studies of erosional forms in bedrock at French River, Ontario, Canada, provide evidence for such floods.

These 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.

[15] Furthermore, hairpin scours around many drumlins are best explained by the erosive action of horseshoe vortices around obstacles in a turbulent boundary layer.

[8] A major drumlin field extends on both sides of the Strait of Magellan covering the surroundings of Punta Arenas' Carlos Ibáñez del Campo Airport, Isabel Island and an area south of Gente Grande Bay in Tierra del Fuego Island.