The Glaciers of the Alps: Being a narrative of excursions and ascents, an account of the origin and phenomena of glaciers and an exposition of the physical principles to which they are relatedTyndall, John
Science
The Glaciers of the Alps: Being a narrative of excursions and ascents, an account of the origin and phenomena of glaciers and an exposition of the physical principles to which they are related
Tyndall, John
Alps -- Description and travel; Glaciers -- Alps
Cases occur, wherein moraines, after having been engulfed, and hidden
for a time, are again entirely disgorged by the glacier. Two moraines
run along the basin of the Talefre, one from the Jardin, the other from
an adjacent promontory, proceeding parallel to each other towards the
summit of the great ice-fall. Here the ice is riven, and profound chasms
are formed, in which the blocks and shingle of the moraines disappear.
Throughout the entire ice-fall the only trace of the moraines is a broad
dirt-streak, which the eye may follow along the centre of the fall, with
perhaps here and there a stone which has managed to rise from its frozen
sepulchre. But the ice wastes, and at the base of the fall large masses
of stone begin to reappear; these become more numerous as we descend;
the smaller debris also appears, and finally, at some distance below the
fall, the moraine is completely restored, and begins to exercise its
protecting influence; it rises upon its ridge of ice, and dominates as
before over the surface of the glacier.
[Sidenote: TRANSPARENCY OF ICE UNDER THE MORAINES.]
The ice under the moraines and sand-cones is of a different appearance
from that of the surrounding glacier, and the principles we have laid
down enable us to explain the difference. The sun's rays, striking upon
the unprotected surface of the glacier, enter the ice to a considerable
depth; and the consequence is, that the ice near the surface of the
glacier is always disintegrated, being cut up with minute fissures and
cavities, filled with water and air, which, for reasons already
assigned, cause the glacier, when it is clean, to appear white and
opaque. The ice under the moraines, on the contrary, is usually dark and
transparent; I have sometimes seen it as black as pitch, the blackness
being a proof of its great transparency, which prevents the reflection
of light from its interior.
The ice under the moraines cannot be assailed in its depths by the solar
heat, because this heat becomes _obscure_ before it reaches the ice, and
as such it lacks the power of penetrating the substance. It is also
communicated in great part by way of contact instead of by radiation. A
thin film at the surface of the moraine-ice engages all the heat that
acts upon it, its deeper portions remaining intact and transparent.
GLACIER MOTION.
PRELIMINARY.
(9.)
[Sidenote: NEVE AND GLACIER.]
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