The earth is made up of several layers. The thin, outermost layer, called the crust is the area that we walk on and is about 18 miles thick. The innermost piece of the earth is called the core and it contains boiling gases, magma and iron. The middle of the earth, in between the outer and inner parts, is called the mantle. This part of the earth contains mostly rock. The Earth’s crust is made up of huge slabs called tectonic plates, which fit together like a jigsaw puzzle.
When two plates collide, one section slides on top of the other, the one beneath is pushed down. These plates sometimes move. Between the earth’s crust and the mantle is a substance called magma, made of molten rock and gases, which then gets squeezed up between the two plates.
As pressure in the Magma builds up deep inside the mountain, it needs to escape somewhere. So it forces its way up “fissures” which are narrow cracks in the earth’s crust and erupts through the volcano mouth. The magma that flows out of a volcano is called lava. Fresh lava ranges from 700° to 1,200° C in temperature and glows red hot to white hot as it flows.
Depending on their nature, volcanoes are classified as ‘active’, ‘dormant’ and ‘extinct’. There are around
1510 ‘active’ volcanoes in the world. Over half of the world’s volcanoes arise in a belt around the Pacific Ocean called the ‘Ring of Fire’. Eighty or more volcanoes are also deep under the oceans. Under-ocean volcanoes are also known to cause Tsunamis and seaquakes.
Some symptoms often precede a volcanic eruption. Steam-blast eruptions could occur with little or no warning, Magmatic eruptions involving the rise of magma toward the surface, which also generate earthquakes and may deform the ground surface might occur. They also tend to cause excessive heat flow or changes in the temperature and chemistry of the ground and spring waters. Both the frequency of occurrence and intensity of felt earthquakes commonly increase before eruptions begin. New or enlarged areas of hot ground may be witnessed.
Since many changes preceding volcanoes are faint, the most effective means of monitoring them are by scientific instruments. However, the nature, exact timing of a volcanic eruption or even its certainty still cannot be pinpointed.
A volcano’s explosion can send debris over an area of up to twenty miles around itself, destroying houses, towns, crops and also cause mudslides and rock-slides, killing many. In fact, the entire ecosystem of an area can be altered by a single volcano eruption. The impact from an eruption can jar the surface of the earth itself, especially if the eruption occurs along the edge of a tectonic plate. If disturbances still exist underground, they can cause anything from large earthquakes to storms and killer waves.
On the other hand, in some cases, volcanic eruptions have been known to be good. In areas with unbalanced ecosystems, volcanoes help restore balance because of the “cleansing” that they bring. Like a forest fire, the volcano destroys an unhealthy ecosystem and gives it the chance to start anew.
Volcanoes create an almost infinite variety of landforms and terrain.However, geologists have noticed patterns when studying these different terrains that allow them to group them into categories, based on how they are the same, and how they are different.These four landform types are called lava flows, volcanic peaks, calderas, and volcanic necks.
FAMOUS VOLCANOES
Mt. Vesuvius – Italy: It is one of the earliest of the most deadly volcanoes. It last erupted in 79 A.D. destroying the cities of Pomeii and Herculaneum.Mt. Tambora - Indonesia : The Mt. Tambora eruption is the most powerful one recorded in history. It last erupted in the year 1815, killing over 71000 people.
Mt. Krakatoa - Indonesia : Mt. Krakatoa exploded in 1883, creating one of the largest eruptions in recorded history.
Mt. Fuji - Japan : Mt. Fuji, a volcanic mountain, is the tallest mountain in Japan. It last erupted in
November 1707
Mt. Pinatubo - Philippines: Mt. Pinatubo, which last erupted in 1991, was the second most powerful volcanic eruption of the 20th Century.
Mt. St. Helens - U.S.A. : Mt. St. Helens last erupted in May 1980, killing 57 people. It is considered the worst volcanic eruption in U.S. history.
Do You Know?
Volcanoes are usually located where tectonic plates meet. This is especially true for the Pacific Ring of Fire, an area around the Pacific Ocean where over 75% of the volcanoes on Earth are found.
While most volcanoes form near tectonic boundaries, they can also form in areas that contain abnormally hot rock inside the Earth. Known as mantle plumes, these hot-spots are found at a number of locations around the globe with the most notable being in Hawaii.
There are also volcanoes found on the ocean floor and even under ice-caps, such as those found in Iceland.
While we certainly have some big volcanoes here on Earth, the biggest known volcano in our solar system is actually on Mars. Its name is Olympus Mons and it measures an astounding 600km (373 miles) wide and 21km (13 miles) high.
Most people think of volcanoes as large cone shaped mountains but that is just one type, others feature wide plateaus, fissure vents (cracks were lava emerges) and bulging dome shapes.
Pumice is a unique volcanic rock that can float in water. It can also be used as an abrasive and is sometimes used in beauty salons and homes for removing dry skin.
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