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Surface Processes
Published in F.G.H. Blyth, M. H. de Freitas, A Geology for Engineers, 2017
F.G.H. Blyth, M. H. de Freitas
‘Plucking’ is thought to occur when rocks, which become lodged in or frozen to the base of the glacier, are separated from their parent mass by glacier movement. A similar plucking action may occur behind the randkluft (Fig. 3.38) on the rock wall at the head of a valley glacier, and in time a steep backed hollow, or corrie is excavated (also called a cirque or cwm). Later this is often occupied by a lake (see Fig. 3.39) as at Glaslyn on Snowdon, in Wales.
Study on three-body abrasive wear behavior of functionally graded Al/TiB2 composite using response surface methodology
Published in Particulate Science and Technology, 2018
The surface plot for distance with respect to speed and load on wear rate is shown in Figures 6 and 7, respectively. The wear rate increases for increasing distance from the outer periphery of the casting at all speeds (Figure 6) and is found reduced at the speed of 75 and 175 rpm on the surface at the distance of 10 mm. The surface at the distance of 1 mm from the outer periphery of the casting has the high reinforced region (Figure 3a). This region is capable to bear the abrasion caused by the silica sand particles, as there is no removal or plucking out of the reinforcement particles due to good bonding between the reinforcement particles and the matrix. This high hard surface thereby reduces the contact area of the matrix with the counter face and results in less wear, where the same phenomenon is observed (Ramesh, Swamy, and Chandrashekar 2012).
Rock fracturing by subglacial hydraulic jacking in basement rocks, eastern Sweden: the role of beam failure
Published in GFF, 2021
Maarten Krabbendam, Romesh Palamakumbura, Christian Arnhardt, Adrian Hall
Hydraulic jacking followed by beam failure and the generation of new vertical fractures can create a dense fracture network in the shallow bedrock. This process represents a form of mechanical weathering, operating subglacially. The jacking and fracturing will thus lower the rock mass strength of the shallow bedrock, so that it is easier to erode, be it by plucking or by glacial ripping (Hall et al. 2020). The jacking and fracturing also greatly increases in hydraulic conductivity of the upper rock mass.
Origin of the Baltic Sea basin by Pleistocene glacial erosion
Published in GFF, 2020
Adrian Hall, Mikis van Boeckel
The present marine basins of the Bothnian, Åland and Baltic Seas fill depressions overdeepened after erosion by the FIS. Overdeepening exploited differences in rock resistance between basement and the sedimentary infill of intra-cratonic basins in the Bothnian and Åland Seas (Amantov et al. 2011). The contributions of different processes of glacial erosion also differed across the two substrates. Abrasion, plucking and ripping were dominant on the basement rocks (Hall et al. in Press); thrusting, rafting and tunnelling were much more significant on sedimentary rocks. The main deeps in the BSB are developed in sedimentary rocks, with 100–200 m high fault-line scarps at basement-sedimentary contacts (Fig. 4). The present submarine Baltic klints are of similar height and stand at similar depths to the BSB deeps. Hence the present-day Baltic klints cannot be inherited pre-glacial structural landforms, modified by glacial erosion (Puura et al. 2003; Tuuling & Flodén 2016), as the bases of the klints lie at depths of up to −150 m below sea level in the East Gotland Basin, far below the reach of fluvial erosion. Instead, the klints are largely glacial features (Amantov et al. 2011), formed as the FIS moved against prominent edges developed in the more massive Ordovician and Silurian sedimentary units in the Early Palaeozoic sequence, as documented by Tuuling & Flodén (2016). On land in northern Estonia, glacitectonic thrusting acting on the Baltic klint led to extensive and deep deformation and faulting, and to the detachment and transport of large rafts of limestone (Rattas & Kalm 2004). That similar processes likely operated beneath the FIS in the present offshore area of the BSB is consistent with widespread evidence for glacitectonic disturbance of pre-existing faults across the scarp and dip slopes of the submerged Baltic and Silurian klints (Tuuling & Flodén 2001). Across wide areas further S on the bed of the Baltic Sea, fault movements occurred in response to regional stress fields and ice loading (Al Hseinat & Hübscher 2017). Here the sub Quaternary surface generally lies >100 m below sea level, a depth that can be attributed to the removal of Palaeozoic to Palaeogene strata by Pleistocene glacial erosion (Uscinowicz 2003).