Topical Guide 568

Mark Dorset

Geographical Features: Drumlin

Where Do You Stop? Chapter 2:

     The hill was actually a mound created by the builder of our house. Before construction began he had scraped the lot bare and flat, plowing all the scrub pine and scrub oak into a mound that ran along the rear property line like a drumlin deposited by a retreating glacier.

Chris D. Clark, “Emergent drumlins and their clones: from till dilatancy to flow instabilities,” in Journal of Glaciology:

Subglacial bedforms are a range of landforms (10-10⁵m long) shaped mostly in glacial sediments and generated by the activity of overriding ice flow. They are abundant on beds of ice sheets dating from the last glaciation, and have recently been observed beneath the Antarctic ice sheet […]. Bedform production by ice sheets seems inevitable, and yields bumps of the order of 10m of relief. Positive elements of this relief have been classified and named according to their size and shape. Flutes are narrow and tens of metres in length […], drumlins are elliptically shaped hills, hundreds to a few thousands of metres long […], mega-scale glacial lineations […] are ridge-groove structures up to 100 km long, and ribbed or Rogen moraines […] are ridges transverse to flow, but are poorly named because they are not actually moraines. Subglacial ribs might be a better term for these latter features.

Mobile till may encounter bedrock knobs and steps, and much like any other mobile medium (wind or water, say) that encounters obstacles, these may become foci for attachment or deposition. Here we name these as obstacle drumlins. Note that while some obstacle drumlins are likely to exist in the bedforms shown in Figure 2, it is improbable that they can all be explained in such a manner. Copyright © 1987. From Boulton, G.S. A theory of drumlin formation by subglacial sediment deformation. In Menzies, J. and J. Rose, eds. Drumlin Symposium. Reproduced by permission of Taylor and Francis Group, LLC, a division of Informa plc. (Via Chris D. Clark, “Emergent drumlins and their clones: from till dilatancy to flow instabilities,” in Journal of Glaciology)

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