Debris-Influenced Sliding Laws and Basal Debris Balance

Abstract

ABSTRACT. In order to determine the effect of basal debris drag as a component in a sliding law, it is necessary to know the basal debris concentration. Does, for example, this debris concentration exhibit uniformity, in an average sense, across a valley? What effect does a localized region of high Quarryability have on basal debris concentration down-stream? The analysis presented here suggests that, for the case of sparse debris, debris concentration tends to be uniform over the entire bed. Consequently, the debris-drag term in a sliding law will also tend to be uniform.In order to reach the above conclusions, it is necessary to consider debris balance, the balance of the Quarrying, abrasion, and debris-flushing rates. This entails proposing and testing Quarrying and flushing laws, since these laws have not been previously proposed. It is concluded that the Quarrying, flushing, and erosion rates depend weakly on the sliding velocity. Furthermore, the abrasion rate is negligible compared to the Quarrying rate. (This conclusion depends partially on the definition of abrasion.) The Quarrying rate also depends on otht'r factors such as the effective pressure-pressure-fluctuation mechanism; the cross-valley dependency of this mechanism is investigated. The flushing rate is found to depend on the ratio, N-channel area/ bed area, and on average N-channel diameter.

Influence of glacier hydrology on the dynamics of a large Quaternary ice sheet

“…Consideration of the manner in which flow processes within the ice sheet adjust to changing subglacial hydrological conditions through time may provide insight into the likely nature of the erosional record left by the ice sheet. It has been argued that the rate of subglacial abrasion scales with the square of the sliding velocity (Hallet, 1979, 19811, while the rate of erosion by quarrying scales directly with the sliding velocity (Shoemaker, 1986). Since different parts of the area covered by the ice sheet had different sliding velocity histories, they might also be expected to exhibit erosional landforms that reflect flow at different stages of the ice sheet's history.…”

Laboratory Simulations Of Glacial Abrasion: Comparison With Theory

“…Field studies (Boulton, 1974; Boulton and others, 1979; Anderson and others, 1982), hampered by the inaccessibility of glacier beds and the logistical difficulty of measuring important parameters in the subglacial environment, have provided insufficient information to evaluate theoretical predictions. Boulton and others (1979) successfully measured fragment-bed contact stresses beneath Glacier d'Argentière, but did not measure the rate of ice convergence toward the bed, a critical variable in most models of abrasion and debris-influenced basal drag (Hallet, 1979, 1981, paper in preparation; Shoemaker, 1986, 1988). In laboratory simulations of abrasion (Lister and others, 1968; Mathews, 1979), neither fragment-bed contact stresses nor rates of ice convergence toward the bed were measured.…”

Cylindrical Flow in and Over Channels of Irregular Shape

“…The inverse technique exhibited here was developed by the author primarily for use in obtaining exact solutions where a sliding law is included, an extension of Shoemaker (in press). In the form exhibited here, the technique is applicable to cold-based glaciers.…”

“…The ratio of the half width of the glacier valley to the depth of valley at the thalweg is w/2h = 2/0.295 ≃ 7, a value which is well within the range of actual glacier valleys. (Shoemaker (in press) presents w/2h values for various glacier and fjord valleys which correspond to the range 1 ≤ w/2h ≤ 10).…”