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Few persons who have not visited Alpine
countries, have a correct idea o f an avalanche.
It is not, as frequently described,
snow set in motion, and accumulated by
rolling, for the noise cannot be produced
by snow rolling over snow. An avalanche
is a mass of snow, sliding from the upper
part of a mountain, and falling over a precipice,
and then striking against the base of
the mountain, or upon the rocks below.
To compare great objects with small, the
snow falling from the roof of a house upon
the pavement, is an avalanche on a small
scale : judge, then, o f the effect, when
many tons, or hundreds of tons of snow
fall from the height of several thousand feet
upon the solid ground. The snow on the
Alps is much consolidated, being partly
changed into ice, by partial thawing and
repeated freezing.
The reason why avalanches are so frequent
from the western side of the Jungfrau,
the Silver Horn, and the Eiger, is,
that the snowy summits of these mountains
slope down rapidly towards the deep chasm
or valley of Trumletenthal, which lies between
them and the Wengen Alp ; the
sides of this chasm are perpendicular, forming
precipices many thousand feet deep.
When the warmth of the afternoon-sun
has thawed a portion of the snow, near the
edge of the precipice, large masses fall over
it into the valley, and one part giving way,
occasions the snow behind to slide down
also, and shoot over the rocks in a continued
stream. As this process is going on,
along a line of five miles in extent, the
avalanches often follow each other in
rapid succession. The snow near the summits
of these mountains is probably more
than 300 feet in depth, so that the diminution
of it, by avalanches, cannot be perceived.
It may be briefly stated, that a sloping
bed of snow, over a precipice, like the
roof of a building above a wall, are essential
conditions for an avalanche, or, at
least, for producing an avalanche which
will be attended with those loud and appalling
sounds, that break in on the silence
of Alpine regions. There may be, and
often is a sliding down of snow, from the
upper to the lower part of the mountains,
without the snow falling over a precipice
; but such avalanches can produce
but little noise.