Erosion



	Glacial Erosion Three Types: Abrasion Images 1. Abrasion Crushing and fracture Cracks, how to make them - pushing down Stress how to set it up with a moving system (Fig. 1) (same as 5.13B in Benn and Evans)/ Micro chatter marks (Plate 7.2 Menzies) Abrasion Rate A=alpha, C, u, F alpha is hardness and bed geometry, C clast concentration, u clast velocity, F effective contact force. How to estimate these last two are the subject of much debate. Example of measurement in Fig. 4. Erosion to Deposition (Fig. 2) Erosion in general 2. Quarrying Facture again in the correct location Figures 7.6 and 7.8 in Menzies are important here. Can you find examples in the images? Role of cavities, when are they present? Once you break it then what? 3. By Water Activity -Mechanical - wear again Abrasion Cavitation -Chemical, Dissolution




		Figure 1. Distribution of normal stress over a bed undulation under sliding conditions (after Boulton, 1974).
						Figure 3. Grain-size distribution per Phi-interval of bedrock and till samples.



		Figure 2. Abrasion of a sinusoidal undulation as a function of effective normal stress according to Boulton theory. Low normal stresses generate a downglacier asymmetric profile with the production of stepped forms and with an associated basin on the downglacier flank. High normal stresses induce lodgement of till (see Chapter 9) on the upgiacier side and an upglacier asymmetry is produced (after Boulton, 1974).				Figure 4. Measured abrasion rates at three experimental locations beneath Breidamerkurjokuli, Iceland. Platens of different material characteristics were used (see key) and of the following hardnesses: marble = 450-510 kg mm-2; basalt = 865-905 kg mm -2; slate = 605-660 kg mm -2; limestone = 180-215 kg mm -2; aluminium = 50-60 kg mm-2. Abrasion rate predicted by Boulton theory is shown as the solid line (after Boulton, 1979).

Glacial Erosion