The great height of Etna has exerted a remarkable influence on its
general conformation: for the volcanic forces have rarely been of
sufficient energy to throw the lava quite up to the crater at the
summit. The consequence has been, that numerous subsidiary craters and
cones have been formed all around the flanks of the mountain, so that it
has become rather a cluster of volcanoes than a single volcanic cone.
The eruptions of this mountain have been numerous, records of them
extending back to several centuries before the Christian era, while
unrecorded ones doubtless took place much further back. After the
beginning of the Christian era, and more especially after the breaking
forth of Vesuvius in 79 A. D., Etna enjoyed longer intervals of repose.
Its eruptions since that time have nevertheless been numerous--more
especially during the intervals when Vesuvius was inactive--there being
a sort of alternation between the periods of great activity of the two
mountains; although there are not a few instances of their having been
both in action at the same time.
SIMILARITY IN ETNA'S ERUPTIONS
There is a great similarity in the character of the eruptions of Etna.
Earthquakes presage the outburst, loud explosions follow, rifts and
bocche del fuoco open in the sides of the mountain; smoke, sand, ashes
and scoriae are discharged, the action localizes itself in one or more
craters, cinders are thrown up and accumulate around the crater and
cone, ultimately lava rises and frequently breaks down one side of the
cone where the resistance is least; then the eruption is at an end.
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