The Geography of the Region about Devil's Lake and the Dalles of the Wisconsin

The Geography of the Region about Devil's Lake and the Dalles of the Wisconsin

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Excerpt: compression would be regarded as ice. 2. Water arising from the melting of the surface snow by the sun's heat, would percolate through the superficial layers of snow, and, freezing below, take the form of ice. 3. On standing, even without pressure or partial melting, snow appears to undergo changes of crystallization which render it more compact. In these and perhaps other ways, a snow-field becomes an ice-field, the snow being restricted to its surface. Eventually the increase in the depth of the snow and ice in a snow-field will give rise to new phenomena. Let a snow and ice field be assumed in which the depth of snow and ice is greatest at the center, with diminution toward its edges. The field of snow, if resting on a level base, would have some such cross-section as that represented in the diagram, Fig. 27 . When the thickness of the ice has become considerable, it is evident that the pressure upon its lower and marginal parts will be great. We Pg 75 are wont to think of ice as a brittle solid. If in its place there were some plastic substance which would yield to pressure, the weight of the ice would cause the marginal parts to extend themselves in all directions by a sort of flowing motion. Fig. 27. -- Diagrammatic cross-section of a field of ice and snow (C) resting on a level base A-B. See larger image Under great pressure, many substances which otherwise appear to be solid, exhibit the characteristics of plastic bodies. Among the substances exhibiting this property, ice is perhaps best known. Brittle and resistant as it seems, it may yet be molded into almost any desirable form if subjected to sufficient pressure, steadily applied through long intervals of time. The changes of form thus produced in ice are brought about without visible fracture. Concerning the exact nature of the movement, physicists are not agreed; but the result appears to be essentially such as would be brought about if the ice were capable of flowing, with extreme...
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Product details

  • Paperback | 56 pages
  • 189 x 246 x 3mm | 118g
  • United States
  • English
  • black & white illustrations
  • 1236719417
  • 9781236719416