Try taking an ice-cube from the refrigeration and rubbing it against a stone from the garden. You will find that not only does the ice melt where it has been in contact with the warmth of your hand, but that it also quickly melts where you have of our hand, but that it also quickly melts where you have been rubbing it, and it has no effect on the stone. Let’s know can glaciers move mountains?
You might think, then, that this is rather a silly question. Of course, you know that glaciers and icebergs are much bigger than ice-cubes and that it is much colder in their surrounding than in your garden. But even the largest glaciers can only push about a fiftieth as hard as would be necessary to break a piece of granite.
In reality, the movement accompanying processes of a glacier in a valley is much more complicated than that of water. In the warmer regions where larger amounts of ice still occur there may be a lot of water melting from the ice which might trickle into the underlying rock and on freezing again would exert enough pressure to shatter it.
There are many scientists who study glaciers, however, who believe that this cannot happen. In any event, these effects are only important in the top few centimeters of the rock and would not account for the removal of a significant amount of rock.
You know that if you compress a spring and then release it, it springs back into its original shape quite violently. In a similar way, all rocks have forces stored within them like a compressed spring, and by removing the top few inches of surface rock these forces may be released with such vigor, so far as the rock is concerned, that the rock may shatter still further. This allows the ice to pick up and carry away more material.
We have said that rock debris is removed by ice. This occurs because as the ices press upon the fragments of rock, the ice tends to melt forming a cavity. The fragment lodged into the cavity and the ice eventually carries it away.
These suspended stones can also aid the erosive power of the glacier in the manner of a piece of glass or emery paper. If you have built balsawood model aircraft, you know the way in which you smooth and round off the leading edges of the wings by rubbing them with glass-paper.
In a similar way, a glacier may carry a large block of rocks jutting from the valley wall, so that smaller fragments can begin their task of smoothing and polishing the remainder.
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