Clark 2010 (5)

Question 1

What are subglacial bedrooms?

Answer 1

Subglacial bedforms are a range of landforms (10–105 m long) shaped mostly in glacial sediments and generated by the activity of overriding ice flow.

Question 2

A rheological model, based on till dilatancy (shear thickening)

Boulton and Jones, 1979; Alley and others, 1986). They proposed the basic conditions necessary for the formation of drumlins in the following words:

Answer 2

i) The glacier–terrain relationship [which we now call ice– bed coupling] . . . was such that at the base of the glacier the terrain material was being continuously deformed. Some of this terrain material [now called the deforming bed] … was carried along by the glacier so that shear deformation occurred within the terrain material.
ii) The deformed layer was composed of a concentrated dispersion of boulders and large rock particles in a dense clay–water system … For drumlins to form, the large particles in this till layer had to form a dilatant system. (Smalley and Unwin, 1968, p. 378)

Question 3

Drumlin formation by subglacial sediment deformation

Answer 3

A mobile and deforming bed that thickens in places to produce bumps that then become streamlined into drumlins.
There appear to be two basic mechanisms for thickening the till layer into such bumps…

• Erosional shaping by streaming till
• Agglomeration at obstacles- obstacles in the path of the flow may become foci for deposition.

Question 4

Numerous explanations for their generation, especially of drumlins, have been proposed. Rather than viewing them as resulting from erosion or deposition directly by ice, Smalley and Unwin (1968) proposed…

Answer 4

that both might occur simultaneously if, beneath the glacier, a layer of lubricating sediment existed and ‘flowed’, conducting geomorphic work (erosion, deposition, shaping) of its own.

Question 5

What does the author conclude?

Answer 5

Subglacial bedforms are emergent phenomena arising from self-organization in the coupled flow of ice, sediment and water.

Question 6

A problem for the instability theory is…

Answer 6

an apparent mismatch between predicted and observed sedimentological properties of bedform.