Volcano
by Roberto Meucci
What is a Volcano? If we wish to make a shaky parallel with dermatology, we could say that in the same way a pimple is the result of a deep inflammatory process, magmatic activity finds outlets through conduits or fissures present in the various strata of the earth's crust to give birth to a volcano.
The earth's crust is formed by various strata, each with different characteristics. Let us examine them from the inside out. First of all, we find the inner nucleus: as we know that seismic waves propagate more rapidly through rigid material, we know that this is solid as opposed to the external nucleus which is liquid and deadens them.
Volcanic eruption
Above this we find the lower mantle or mesosphere, it too composed of solid rock. Then comes the asthenosphere composed of almost plastic rock which absorbs the speed of the seismic waves, deforming without breaking. Finally we reach the lithosphere, the earth's rigid outer crust. And it is precisely the rigidness of this crust to create seismic or volcanic activity in the vicinity of the fault lines: the points of contact of the pieces of this immense puzzle which is the earth's surface.
Volcanoes are the result of magmatic activity, a molten mass composed of silicates, at a pressure that provokes fractures through which the magma can escape either on the earth's crust or below the seas. The Suboceanic Range, or belt of fire, is the world's most imposing mountain range, though invisible to our eyes because almost completely under water. It is an uninterrupted chain of volcanoes about 60,000 km long, 1,000 km wide and 3 km high.
The floor of the Oceans, two-thirds of the earth's surface, is formed by lava, molten rock that has cooled and solidified; reascending magma has provoked its expansion and continental drift. In order to move hundreds of millions of cubic kilometres, by means of the viscosity of magma on which the continental blocks rest, an enormous amount of energy is needed to provoke the fractures and fissures through which the magma finds its way out to the surface, either subaqueous or subaerial, and then cools, making the continents' change of position definite.
To summarise: phenomena of volcanic activity occur when two pieces of the mosaic that forms the earth's surface drift apart sufficiently to allow magma to reascend. Furthermore, an examination of the solidified lava reveal the variation of the Poles in the course of geological eras. The basalts, essential component of the ocean floors, are rocks rich in magnetite (Fe304), an iron oxide whose crystals, contained in lava, assume a magnetic orientation parallel to that of the earth's field, thus indicating the magnetic North of the epoch in which the lava cooled.
Following these indications of the rocks, we know that in the last four million years there have been twenty-two inversions in the polarity of the planet. We can thus say that volcanism is the point of departure for our knowledge of visible lands and ocean floors till now explored.
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