Fragments of Science: A Series of Detached Essays, Addresses, and Reviews. V. 1-2Tyndall, John
Science
Fragments of Science: A Series of Detached Essays, Addresses, and Reviews. V. 1-2
Tyndall, John
Chemistry; Physics; Science
This deportment explains an appearance which must strike every
observer who looks upon the Morteratsch from the Piz Languard, or from
the new Bernina Road. A medial moraine runs along the glacier,
commencing as a narrow streak, but towards the end the moraine
extending in width, until finally it quite covers the terminal portion
of the glacier. The cause of this is revealed by the foregoing
measurements, which prove that a stone on the moraine where it is
crossed by the line A approaches a second stone on the moraine where
it is crossed by the line C with a velocity of twenty-six inches per
one hundred hours. The moraine is in a state of longitudinal
compression. Its materials are more and more squeezed together, and
they must consequently move laterally and render the moraine at the
terminal portion of the glacier wider than above.
The motion of the Morteratsch glacier, then, diminishes as we descend.
The maximum motion of the third line is thirty inches in one hundred
hours, or seven inches a day--a very slow motion; and had we run a
line nearer to the end of the glacier, the motion would have been
slower still. At the end itself it is nearly insensible. [Footnote:
The snout of the Aletsch Glacier has a diurnal motion of less than two
inches, while a mile or so above the snout the velocity is eighteen
inches. The spreading out of the moraine is here very striking.] Now
I submit that this is not the Place to seek for the scooping power of
a glacier. The opinion appears to be prevalent that it is the snout
of a glacier that must act the part of ploughshare; and it is
certainly an erroneous opinion. The scooping power will exert itself
most where the weight and the motion are greatest. A glacier's snout
often rests upon matter which has been scooped from the glacier's bed
higher up. I therefore do not think that the inspection of what the
end of a glacier does or does not accomplish can decide this question.
The snout of a glacier is potent to remove anything against which it
can fairly abut; and this power, notwithstanding the slowness of the
motion, manifests itself at the end of the Morteratsch glacier. A
hillock, bearing pine-trees, was in front of the glacier when Mr.
Hirst and myself inspected its end; and this hillock is being bodily
removed by the thrust of the ice. Several of the trees are
overturned; and in a few years, if the glacier continues its reputed
advance, the mound will certainly be ploughed away.
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