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TEXT STUDY THE ORIGIN OF VOLCANOES


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TEXT STUDY THE ORIGIN OF VOLCANOES

Message non lu par salogo hamed » mer. 23 sept. 2020 14:49

TEXT STUDY :THE ORIGIN OF VOLCANOES

For thousands of years people have tried to understand the causes of volcanoes. The
early Greeks and Romans thought that the forge of the god Vulcan was on a small island in
the Mediterranean Sea. There was a mountain on the island. From the mountain came fire and
loud noises. The Greeks and Romans thought that the fire and noise came from Vulcan’s
anvil; there he hammered out the god’s thunderbolts. People called the island Vulcan. From
that name comes the word “volcano.”
Now we know more about volcanoes. However, we are unable to explain them
completely. Here are some agreed upon-facts. All volcanoes have two things in common: an
opening or openings in the earth and materials which go from the interior of the earth to its
exterior through the opening. The hot, molten materials inside the earth are called “magma”,
the Latin word for dough. These materials form an intrusion. When the magma leaves the vent
or opening in the earth, it exits in the form of gases, lava, liquid or solid materials. The gases,
lava and solid matter are extrusions.
When these materials come out of the earth, they form a cone. At the top or on the
sides of a volcano is a crater or hole. Volcanoes erupt, that is to say, explode, in different
ways. The kind of eruption depends partly on the types of ejected materials.
There are two basic types: basaltic rock lava, which is soft and flows easily and
granitic silica lava, which is hard. Granitic lavas keep gases inside the volcano until the
pressure becomes very great. Then an explosion of gases throws soft and solid materials
violently into air. The particles of matter are of many different sizes, from huge rocks to fine
ash.
There are three stages in the life of a volcano. It may be active, dormant or extinct.
“Dormant” means “sleeping.” That is, the volcano is not active but could become active. An
“extinct” volcano is no longer alive or active. However, dormant volcanoes can become active
very suddenly. That was the case with Mount St Helens in the state of Washington on May
18, 1980.
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