Stromboli is the principal of the cluster of small islands, lying to the
north of Sicily, named the Lipari isles, the whole of which contain
volcanoes. At a distance, its form appears to be that of an exact cone,
but on a closer examination it is found to be a mountain having two
summits of different hights, the sides of which have been torn and
shattered by craters. The most elevated summit, inclining to the
south-west, is, agreeably to Spallanzani, about a mile in hight.
In this volcanic mountain, the effects of a constantly active fire are
everywhere visible, heaping up, destroying, changing, and overturning
every instant what itself has produced, and incessantly varying in its
operations. At the distance of one hundred miles, the flames it emits
are visible, whence it has been aptly denominated the light-house of
that part of the Mediterranean sea.
From the more elevated summit, all the inner part of the burning crater,
and the mode of its eruption, may be seen. It is placed about half-way
up, on the north-west side of the mountain, and has a diameter not
exceeding two hundred and fifty feet. Burning stones are thrown up at
regular intervals of seven or eight minutes, ascending in somewhat
diverging rays. While a portion of them roll down toward the sea, the
greater part fall back into the crater; and these being again cast out
by a subsequent eruption, are thus tossed about until they are broken
and reduced to ashes. The volcano, however, constantly supplies others,
and seems inexhaustible in this species of productions. Spallanzani
affirms that, in the more violent eruptions, the ejected matter rises to
the hight of half a mile, or even higher, many of the ignited stones
being thrown above the highest summit of the mountain.
The erupted stones, which appear black in the day-time, have at night a
deep red color, and sparkle like fire-works. Each explosion is
accompanied by flames or smoke, the latter resembling clouds, in the
lower part black, in the upper white and shining, and separating into
globular and irregular forms. In particularly high winds from the south
or south-east, the smoke spreads over every part of the island.
Spallanzani observed this volcano on a particular night, when the latter
of these winds blew with great violence. The clear sky exhibited the
appearance of a beautiful aurora borealis over that part of the mountain
on which the volcano is situated, and which from time to time became
more red and brilliant, in proportion as the ignited stones were thrown
to a greater hight. The violence of the convulsions depends on that of
the wind.
The present crater has burned for more than a century, without any
apparent change having taken place in its situation. The side from which
the showers of ignited matter fall into the sea, is almost
perpendicular, about half a mile broad at the bottom, and a mile in
length, terminating above in a point. In rolling down, the lava raises
the fine sand like a cloud of dust. While this was observed by
Spallanzani, the volcano suddenly made an eruption. Numerous pieces of
lava of a dark red color, and enveloped in smoke, were ejected from the
top of the precipice, and thrown high into the air. A part of them fell
on the declivity, and rolled down, the smaller preceded by the greater;
after a few bounds, dashing into the sea, giving out a sharp hissing
sound. The more minute fragments, from their lightness, and the
hindrance of the sand, rolled slowly down, and striking against each
other, produced nearly the same sound as hail-stones falling on a roof.
In a few minutes another explosion followed, without any sensible noise;
and two minutes after a third eruption took place, with a much louder
explosion than the first, and a far more copious ejection of lava. The
eruptions, which were almost innumerable during the time Spallanzani
remained there, all exhibited the same appearances.
On the night following the one above described, the volcano raged with
still greater violence, and rapidly hurled to a great hight, thousands
of red-hot stones, forming diverging rays in the air. Those which rolled
down the precipice, produced a hail of streaming fire, which illuminated
the steep descent. Independently of these ignited stones, there was in
the air which hovered over the volcano, a vivid light, which was not
extinguished when that was at rest. It was not properly flame, but real
light reverberated by the atmosphere, impregnated by extraneous
particles, and more especially by the ascending smoke. Besides varying
in intensity, it appeared constantly in motion, ascending, descending,
dilating and contracting, but always remaining perpendicular over the
mouth of the volcano, which showed that it was occasioned by the
conflagration within the crater. The detonations in the greater
eruptions resembled the roaring of distant thunder, and in the lesser
ones, the explosions of a mine. In the smallest they were scarcely
audible. Each was some seconds later than the ejection.
Near the mouth of the volcano is a small cavern, a projection above
which secures it from the entrance of the ignited stones. From this
cavern Spallanzani was enabled to look down into the very bowels of the
volcano. He describes the edges of the crater as of a circular form, and
not more than three hundred and forty feet in circumference, the
internal sides contracting as they descend, and assuming the shape of a
truncated inverted cone. The crater itself, to a certain hight, is
filled with a liquid red-hot matter, resembling melted brass. This is
the fluid lava, which appears to be agitated by two distinct motions,
the one intestine, whirling and tumultuous, and the other that by which
it is impelled upward. This liquid matter is raised, sometimes with
more, and sometimes with less rapidity, within the crater; and when it
has reached within twenty-five or thirty feet of the upper edge, a sound
is heard not unlike a short clap of thunder, while at the same moment a
portion of the lava, separated into a thousand pieces, is thrown up with
indescribable swiftness, accompanied by a copious eruption of smoke,
ashes and sand. A few moments before the report, the superficies of the
lava is inflated and covered with large bubbles, some of which are
several feet in diameter; on the bursting of these the detonation and
fiery shower take place. After the explosion, the lava within the crater
sinks, but soon rises again as before, and new bubbles appear, which
again burst and produce new explosions. When the lava sinks, it gives
little or no sound; but when it rises, and particularly when it begins
to be inflated with bubbles, it is accompanied by a noise similar, in
proportion to the difference of magnitude, to that of liquor boiling
vehemently in a caldron.