Only a few spectacular eruptions are so violent that they blown the mountain apart. People for thousands of years have been fascinated by the spectacle of volcanic eruptions and terrified of their power. Some of these eruptions have caused some of the worst disasters in history, by wiping out entire towns and killing thousands of people. The word volcano comes from the term Vulcan, which was a name the ancient Romans gave their god of fire. Volcanoes played a role in the religious life of some of these people, and they believed that god lived beneath a volcanic island off the Italian coast.
Powerful forces within in the earth’s surface cause the formation of volcanoes. Volcanoes begin as magma, deep inside the earth, which is caused by the extreme heat within the earth’s interior. Magma develops from 15 to 100 miles beneath the earth’s surface, where it is melted and releases gas. Gradually the magma rises toward the earth’s surface because it is lighter than the solid rock around it. As the magma rises, it melts gaps in the surrounding rock and forms a large chamber two miles from the surface.
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An eruption takes place when the gas-filled magma under ground is under read pressure from the solid rock around it and this pressure causes the magma to blast, or melt a conduit in a weakened part of the rock. The magma moves through the conduit toward the surface and when it reaches the surface, the gas and magma are released. When magma and gas reach the surface, they get blown out an opening called the central went. This is the main site where most of the volcanic eruption takes place. As the magma gradually builds up over time, it forms a volcanic mountain or volcano.
Once a volcano is formed, many different situations can occur. Most of the magma in further eruptions does not reach the surface through the central vent. Most Of the magma is sent out through conduit walls, and form small channels of lava, while some just stay below the surface walls. Only a small fraction of the time will the volcano blow out of its main vent again. There are three basic kinds of materials that are erupted from a volcano, lava, rock fragments, and gas. This material depends chiefly on how sticky or how fluidly a volcano’s magma is. Lava is the name for magma, which has been released upon the earth’s surface.
It is red hot and has a temperature of more than 2012 degrees Fahrenheit. Highly fluid lava flows more rapidly while sticky lave flows slowly. As lava cools it forms many different formations, ranging from smooth folded sheets to jagged sheets. Rock fragments are formed from sticky magma, that is so sticky that its gas cannot easily escape when the magma approaches the surface or central vent. The trapped gas builds up so much pressure that it blasts the magma into fragments. These fragments can be as small as volcanic dust, or can be as big as chunks of rock.
During most eruptions large quantities of gas are let out into the air. A few of these gases include carbon dioxide, nitrogen, and sulfur dioxide. The combination of gas and volcanic dust make the air look like it has black smoke. There are many volcanoes in the world today. Most are in or around the Pacific Ocean, forming a ” Ring of Fire. ” They are formed here because of the continental drift, which is a theory that says the Earth’s crust is divided into thin moving plates. As these plates move, the new land pushes the thin plates causing their movements, which results in a volcano.
Volcanic activity also occurs in such places as Hawaii, Iceland, and southern Europe. Another way volcanoes can be formed is when plates move. When two plates collide, one is forced under the other. As the plate sinks, friction and the earth’s heat cause part of it to melt. The melted part then rises as magma, and then when it reaches the surface it forms a volcano. Volcanic activity also occurs when two plates spread apart, which usually happens on the ocean floor. As the plates move apart, magma below the crust moves up between the plates and pour onto the ocean floor.
There are typically four different types of volcanoes: Cinder, Shield, Composite, and Lava Domes. Cinder Cones are the simplest type of volcano. They are build from blobs of lava and ejected through a single vent. As the lava is blown into the air, it breaks up into small fragments and solidifies. Most cinder cones have a bowl-shaped crater at the summit and rarely rise more than a thousand feet above their surroundings. These are numerous in western North America as well as throughout other volcanic terrains of the world. The picture below is of Parasitic in western Mexico.
In began in 1943, hen a crack opened in the ground Of a cornfield. It grew to be 1,345 feet high, before it erupted in 1952. Shield volcanoes are made of slow lava flows, which can travel far. The resulting volcanic landforms as a broad base and very gentle slope, which looks much like a warrior’s inverted shield. This photo is from a lava flow in the upper northeast rift zone of Manna Lola. Composite Volcano’s are generally steep-sided, symmetrical cones of large dimension built of alternating layers of lava flow, volcanic ash, cinders, blocks, and bombs and may rise as much as 8,000 feet above their bases.