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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It Was Eight In The
Morning, And We Suffered Severely From The Cold, Though The
Thermometer Kept A Little Above Freezing Point.
For a long time we
had been accustomed to a very high temperature, and the dry wind
increased the feeling of cold, because it carried off every moment
the small atmosphere of warm and humid air, which was formed around
us from the effect of cutaneous perspiration.
The brink of the crater of the peak bears no resemblance to those
of most of the other volcanoes which I have visited: for instance,
the craters of Vesuvius, Jorullo, and Pichincha. In these the Piton
preserves its conic figure to the very summit: the whole of their
declivity is inclined the same number of degrees, and uniformly
covered with a layer of pumice-stone very minutely divided; when we
reach the top of these volcanoes, nothing obstructs the view of the
bottom of the crater. The peaks of Teneriffe and Cotopaxi, on the
contrary, are of very different construction. At their summit a
circular wall surrounds the crater; which wall, at a distance, has
the appearance of a small cylinder placed on a truncated cone. On
Cotopaxi this peculiar construction is visible to the naked eye at
more than 2000 toises distance; and no person has ever reached the
crater of that volcano. On the peak of Teneriffe, the wall, which
surrounds the crater like a parapet, is so high, that it would be
impossible to reach the Caldera, if, on the eastern side, there was
not a breach, which seems to have been the effect of a flowing of
very old lava. We descended through this breach toward the bottom
of the funnel, the figure of which is elliptic. Its greater axis
has a direction from north-west to south-east, nearly north 35
degrees west. The greatest breadth of the mouth appeared to us to
be 300 feet, the smallest 200 feet, which numbers agree very nearly
with the measurement of MM. Verguin, Varela, and Borda.
It is easy to conceive, that the size of a crater does not depend
solely on the height and mass of the mountain, of which it forms
the principal air-vent. This opening is indeed seldom in direct
ratio with the intensity of the volcanic fire, or with the activity
of the volcano. At Vesuvius, which is but a hill compared with the
Peak of Teneriffe, the diameter of the crater is five times
greater. When we reflect, that very lofty volcanoes throw out less
matter from their summits than from lateral openings, we should be
led to think, that the lower the volcanoes, their force and
activity being the same, the more considerable ought to be their
craters. In fact, there are immense volcanoes in the Andes, which
have but very small openings; and we might establish as a
geological principle, that the most colossal mountains have craters
of little extent at the summits, if the Cordilleras did not present
many instances to the contrary.* (* The great volcanoes of Cotopaxi
and Rucupichincha have craters, the diameters of which, according
to my measurements, exceed 400 and 700 toises.) I shall have
occasion, in the progress of this work, to cite a number of facts,
which will throw some light on what may be called the external
structure of volcanoes.
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