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Sediments and Sedimentary Rocks
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
Sometimes, moving glacial ice reworks (modifies) previously deposited glacial material. When glaciers advance over older till, for example, they can produce drumlins such as the ones shown in Figure 8.36. Drumlins are elongated, asymmetrical, oval hills of glacial debris that formed under moving ice. These streamlined mounds have a steep slope on their front face (down and to the left in the photo) that records the direction of glacial flow and may be up to 2 kilometers (1.25 miles) long. Drumlins are often found in groups called drumlin fields. Some spectacular drumlin fields are found in the Great Lakes region of North America, including the field in Wisconsin shown in Figure 8.36. The largest Great Lakes drumlin field is in western New York, where more than 10,000 drumlins are associated with the glacially scoured Finger Lakes. These drumlins formed during an ice age about 18,000 years ago, near the terminus of a continental ice sheet that covered Canada and the northernmost United States.
Superficial deposits
Published in A.C. McLean, C. D. Gribble, Geology for Civil Engineers, 2017
The formation of drumlins (see Fig. 3.16) is described elsewhere (Section 3.5.5). They typically occur in a swarm, and any ground between individual drumlins is left poorly drained and possibly ponded. A typical drumlin is 0.5-1.0 km in length in the direction of ice flow, and half that in maximum width. Its height lies in the range 50-100 m. Its blunter, steeper end was formed on the upstream side of the ice flow, and its tail in the lee. The hill is formed mainly, or entirely, of till. Some drumlins have a small rock core, seldom more than a fraction of the size of the drumlin, which may have encouraged deposition from the ice. Others are simply mounds of till on an irregular glaciated surface, and the height of the drumlin is a measure of the thickness of the superficial deposit. There is no certain way of discriminating between these two extreme possibilities from the form of the drumlin.
Glacial geology
Published in Barry G. Clarke, Engineering of Glacial Deposits, 2017
Drumlins can occur on their own or in fields of several thousands. Their height varies from 10 to 50 m and their length from 50 m to 20 km. They are typically smooth oval or elliptical shaped with the major to minor axis varying between 1.5 and 4.1 (Hambrey, 1994). They can be formed of lodgement till, bedrock, mixtures of glacial soils and sands and gravels. There are several suggestions as to how drumlins are formed including products of subglacial deformation, subglacial lodgement, fluvial infills, remnants of subglacial floods, or products of melting of debris-rich ice. Boulton (1987) suggested that subglacial deformation (Figure 2.19) is the most likely with drumlins forming around some obstacle as the ice erodes the softer material adjacent to the obstacle and deforms the obstacle. Figure 2.20 shows possible drumlin formation because of changes in the bedrock surface, which leads to the subglacial deforming till rising over the bedrock obstruction to create a drumlin. Figure 2.21 is the suggestion that drumlin formation is a consequence of a fold generated in the lower deforming zone and around glaciofluvial deposits formed during the last ice retreat. A deforming basal layer moving across pro-glacial meltwater streams, which have deposited gravel (Figure 2.22), can also lead to drumlins. These four models, based on excavations, depend on the characteristics of the surface, the ice and the deforming substrate. It is difficult to prove these models because observations beneath glaciers are difficult.
Production and preservation of the smallest drumlins
Published in GFF, 2018
J. K. Hillier, Í. Ö. Benediktsson, T. P. F. Dowling, A. Schomacker
Drumlins are subglacial bedforms aligned parallel to ice flow, created by interactions in the ice–sediment–water system underneath glaciers or ice-sheets (e.g., Menzies 1979; Clark et al. 2009; Benn & Evans 2010). Their mode of formation remains enigmatic and debated (Smalley & Unwin 1968; Menzies 1979; Shaw 1983; Boulton & Hindmarsh 1987; Hindmarsh 1998; Fowler 2000), primarily because the bases of modern ice sheets are inaccessible, which results in few direct observations (King et al. 2007; Smith & Murray 2009). Mapped morphometrics of the numerous (i.e., >>10 000) drumlins formed during past glaciations (e.g., Hättestrand et al. 2004; Storrar & Stokes 2007; MacLachlan & Eyles 2013) are therefore key to understanding the subglacial interface, despite less readily yielding secure conclusions about the dynamics and mechanics of former ice sheets.
Drumlin formation: a mystery or not?
Published in GFF, 2018
Anders Schomacker, Mark D. Johnson, Per Möller
This special issue of GFF is devoted to drumlins, surely the most-studied glacial landform that exists (Fig. 1). Drumlins have caught the attention of geoscientists because of their elegant shape, their demonstrated orderliness, and their clear relationship to the flow of glaciers. Perhaps it is also their usually “manageable size” (both physically and psychologically) that have made them the subject of such considerable research. In recent years, during which glacial geology and geomorphology have been better integrated with glaciology and palaeoglaciology, drumlins have become even more of interest as they can give us insight into bed conditions and bed processes of former and current glaciers. The recent availability of high-resolution digital elevation models also play a key role in stimulating new and recent drumlin research (e.g., Allaart et al. 2018; Hillier et al. 2018; Möller & Dowling 2018; Sookhan et al. 2018).
Drumlins in the Nordenskiöldbreen forefield, Svalbard
Published in GFF, 2018
Lis Allaart, Nina Friis, Ólafur Ingólfsson, Lena Håkansson, Riko Noormets, Wesley R. Farnsworth, Jordan Mertes, Anders Schomacker
The subglacial landform drumlin has received far more attention than any other subglacial landform (Menzies & Rose 1987; Stokes et al. 2011). Drumlins are observed both in marine and terrestrial settings, and their origin has challenged glacial geologists for decades (Wright Jr 1957; Menzies & Rose 1987; Fader et al. 1997; Greenwood & Clark 2009; Benn & Evans 2010). The quest for a unifying theory of drumlin formation, composition and shape has been one strong focus of drumlin research, and has resulted in numerous publications of varying conceptual and theoretical models for drumlin formation (e.g., Smalley & Unwin 1968; Shaw 1983; Boulton 1987; Menzies & Rose 1987; Hart 1997; Stokes et al. 2011; Spagnolo et al. 2012; Dowling 2016; Iverson et al. 2017). The morphology of a drumlin is classically described as a smooth, oval, half egg-shaped hill with a blunt stoss side and a tapering lee side (Menzies 1979). The landform is thought to be part of a larger array of subglacial bedforms: drumlins, drumlinoids, crag-and-tails, flutes, glacial lineations, mega-flutes and mega-scale glacial lineations (MSGL), and they form parallel to ice flow direction as a result of dynamic interaction between glaciers and their substratum (Benn & Evans 2010). Drumlins often appear in swarms of tens to thousands of landforms (Wright Jr 1957; Smalley & Unwin 1968; Glückert 1973; Menzies 1979; Dardis et al. 1984; Shaw & Kvill 1984; Krüger 1987; Piotrowski 1987; Rose 1987; Fader et al. 1997; Kjær et al. 2003; Briner 2007; Clark et al. 2009; Hughes et al. 2010; Johnson et al. 2010; McCracken et al. 2016; Möller & Dowling 2016).