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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
Figure 8.30 shows a cross section of an alpine glacier. For alpine glaciers, snow accumulation is most significant at high elevations near the glacier’s head, in a region called the accumulation zone. For continental glaciers, snow accumulation is generally greatest in cold climate regions closest to the north or south poles. As snow accumulates, fresh snow compacts the snow beneath it. In both continental and alpine glaciers compaction, crushing, recrystallization, some melting, and refreezing eventually transform snow into firn, an intermediate product, and eventually into glacial ice. Layers of snow, firn, and ice are highlighted in Figure 8.30. As snow becomes ice, porosity decreases from more than 80% to nothing over one to several years, and consequently glacial ice is much denser than the snow from which it forms. Glacial ice, the snow, and firn riding on it, and suspended material within it flow downhill under the influence of gravity or outward from polar origins. Typically, flow rates are on the order of meters/day for alpine glaciers but range from less than a meter/year to as much as 30 meters/day. Continental ice sheets, by comparison, flow much slower.
The glacier sedimentary system
Published in Richard J. Chorley, Stanley A. Schumm, David E. Sugden, Geomorphology, 2019
Richard J. Chorley, Stanley A. Schumm, David E. Sugden
Snow in the accumulation zone undergoes a series of changes which transform it to glacier ice. The term firn is generally applied to snow which has survived a summer melt season and has begun this transformation. It consists of loosely consolidated, randomly oriented ice crystals with interconnecting air passages and a density generally greater than 0.4 mg/m3. Transformation involves the regrowth of ice crystals and the elimination of air passages. When consolidation has proceeded sufficiently to isolate the air into separate bubbles, the firn becomes glacier ice. This change to ice takes place at densities of between 0.8 and 0.85 kg/m3. At higher temperatures, and especially in the presence of water, transformation to ice can take place within one year. In cold subzero environments, such as on the Antarctic ice sheet, transformation may take several thousand years.
Dynamic behaviour of miniature laser textured skis
Published in Surface Engineering, 2020
Francesco Ripamonti, Valentina Furlan, Alessandro Savio, Ali Gökhan Demir, Federico Cheli, Paolo Ossi, Barbara Previtali
Scientific investigations of ice/snow friction began around the mid-nineteenth century. M. Faraday studied the contact between two ice cubes. His conclusions were clear: ice surface is covered by a liquid-like layer [12], entirely governing the friction mechanism. This result was the starting point for further researches. About 80 years later, Bowden and Hughes suggested that frictional heating, leading to ice melting, was the main contribution to ice friction problems [7]. This approach is nowadays the generally accepted theory to explain friction not only on ice but also on snow. This is not surprising once we keep into account that snow, after being deposited, is a highly porous, sintered material made of continuous ice skeleton and a continuously connected pore space, that kept together constitute the snow microstructure [13]. The time elapsing snow metamorphism leads to material densification, formation of firn and later to ice. Not surprisingly, the exhaustive review on snow friction provided by Colbeck [8], shows that many similarities exist between snow and ice friction [14]. Experiments on ice are preferred because, given its structural and mechanical stability, its behaviour is less complex [7,9,15-18]. The sliding friction on ice is determined by many factors, such as temperature [9-11,15,19-25], sliding velocity [20,26-31], normal force [15,20,30], apparent contact area [7,17,21], roughness [24,32-34], surface wettability [16,34,35], surface morphology that is commonly known as ‘texture’ [24,34], relative humidity [27] and thermal conductivity [24,28]. All these factors affect the thickness and continuity of the liquid-like layer at the interface between the sliding body and the cold ice surface. This layer is generated by the heating associated with friction that melts part of the ice on the surface [9,14]. However, it is not always easy, nor is it convenient, to investigate the effect of a single parameter without considering its interdependence with other factors. For instance, in this context, the effect of wettability is often investigated in combination with other material parameters, such as roughness, texture and thermal conductivity [16,34,35]. Concerning this, many studies [36-43] show that friction on ice is lower for surfaces presenting a hydrophobic behaviour. Benefits are expected, especially close to the ice melting point [9,16,18,34,35], but also at lower temperatures where the melted liquid-like layer is lacking [9].