Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 1 - By Alexander Von Humboldt And Aime Bonpland.
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This Structure Is As Varied As The Volcanic
Phenomena Themselves; And In Order To Raise Ourselves To Geological
Conceptions Worthy Of The Greatness Of Nature, We Must Set Aside
The Idea That All Volcanoes Are Formed After The Model Of Vesuvius,
Stromboli, And Etna.
The external edges of the Caldera are almost perpendicular.
Their
appearance is somewhat like the Somma, seen from the Atrio dei
Cavalli. We descended to the bottom of the crater on a train of
broken lava, from the eastern breach of the enclosure. The heat was
perceptible only in a few crevices, which gave vent to aqueous
vapours with a peculiar buzzing noise. Some of these funnels or
crevices are on the outside of the enclosure, on the external brink
of the parapet that surrounds the crater. We plunged the
thermometer into them, and saw it rise rapidly to 68 and 75
degrees. It no doubt indicated a higher temperature, but we could
not observe the instrument till we had drawn it up, lest we should
burn our hands. M. Cordier found several crevices, the heat of
which was that of boiling water. It might be thought that these
vapours, which are emitted in gusts, contain muriatic or sulphurous
acid; but when condensed, they have no particular taste; and
experiments, which have been made with re-agents, prove that the
chimneys of the peak exhale only pure water. This phenomenon,
analogous to that which I observed in the crater of Jorullo,
deserves the more attention, as muriatic acid abounds in the
greater part of volcanoes, and as M. Vauquelin has discovered it
even in the porphyritic lavas of Sarcouy in Auvergne.
I sketched on the spot a view of the interior edge of the crater,
as it presented itself in the descent by the eastern break. Nothing
is more striking than the manner in which these strata of lava are
piled on one another, exhibiting the sinuosities of the calcareous
rock of the higher Alps. These enormous ledges, sometimes
horizontal, sometimes inclined and undulating, are indicative of
the ancient fluidity of the whole mass, and of the combination of
several deranging causes, which have determined the direction of
each flow. The top of the circular wall exhibits those curious
ramifications which we find in coke. The northern edge is most
elevated. Towards the south-west the enclosure is considerably sunk
and an enormous mass of scorious lava seems glued to the extremity
of the brink. On the west the rock is perforated; and a large
opening gives a view of the horizon of the sea. The force of the
elastic vapours perhaps formed this natural aperture, at the time
of some inundation of lava thrown out from the crater.
The inside of this funnel indicates a volcano, which for thousands
of years has vomited no fire but from its sides. This conclusion is
not founded on the absence of great openings, which might be
expected in the bottom of the Caldera. Those whose experience is
founded on personal observation, know that several volcanoes, in
the intervals of an eruption, appear filled up, and almost
extinguished; but that in these same mountains, the crater of the
volcano exhibits layers of scoriae, rough, sonorous, and shining.
We observe hillocks and intumescences caused by the action of the
elastic vapours, cones of broken scoriae and ashes which cover the
funnels.
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