What is a Volcano?
A volcano is vent or opening on planet’s surface which allows molten rock called magma, volcanic ash and gas to escape out onto its surface. A volcano gives a look like a mountain from which lava erupts. The hot magma erupting from a volcano is called lava. When that lava cools down, it becomes solid and forms like a mound-like cone. In fact the mountain that we see today are nothing but solidified lava from previous volcanic eruptions.
It is said that through volcanoes are earth’s way of renewing itself. This may be the case or not but volcanoes are definitely one of the most eminent features of nature. They are reason to creation of beautiful places like Costa Rica, Hawaii chain islands, Nicaragua and are spectacular display of magnanimity of nature. But what gives rise to these magma spewing colossal figures.
States Of Volcano
A volcano can be active, dormant or extinct state. An active volcano is one that is erupting lava, gas and shows some signs of seismic activity. A dormant volcano is one that has not erupted for quite a long time and can erupt again anytime in future while an extinct volcano is one that has been dormant for over 2,000 years and has not shown any sign if activity.
Formation Of Volcanoes
What’s Inside Earth?
Before we get to that we would have to get a briefing on the structure of planet Earth. The interior structure of earth consists of a core which is divided into inner and outer core, followed by highly viscous mantle and lastly the solid crust. The inner core is solid whereas outer core is liquid and so is mantle though a fact to be noted is that the viscosity of outer core is higher a lot higher than the viscosity of the mantle. Due to high pressure and heat the mantle is in viscous liquid state and not solid.
Tectonic Plates and Formation Of Volcanoes
This is the reason why the crust or tectonic plates are in motion as they are basically floating in mantle. Though this motion is very slow and takes a long period of time to notice a visible difference but the tectonic plates are in a constant state of motion. They are either converging or going apart.
Formation of a volcano may takes place on either of the occasion irrespective of the direction of the movement of the tectonics plates. Mid Atlantic Ridge is an example volcano formation where the tectonics plates are diverging or pulling apart whereas Pacific Ring of Fire is an example of volcano caused due to convergence of tectonic plates.
On many occasions these tectonic plates are on a collision course and when such an event occurs due to extreme pressure one of the plate’s slides over the other. One of the tectonic plates is forced into the mantle and other rise above the other one. Due to the extreme pressure and heat in the mantle the solid tectonic plate melts and rock complete melt and forms what is known as magma. This molten material rises due to many reasons such as releasing of heat and buoyancy tries to escape and makes it ways through the crust.
Most the time but not necessarily always the molten material or magma makes its way through the earth surface through the cracks and exert pressure to escape. When this magma reaches surface, it gives rise to volcanoes. Magma reaching the surface of the earth is referred as lava. Over the period of time through constant eruption, layer by layer of lava builds up a volcano.
The eruption occurs in the through the weak portions on the earth surface through which magma is able to makes it way out. This overall process takes place as a form of pressure and heat release from within the earth. Such magma outburst may be accompanied by strong earthquakes. You can get more information of the various types of lava flow and there resultant volcano.
There are numerous factors which determine the flow of the lava, the course taken by it and the type of volcano formation that might occur. Such factors include the pressure in the given area, the mineral content, the amount of gas and molten material, all are contributing factors in an eruption and as well as formation of a volcano. There are many categories of volcanoes including Stratovolcanoes or composite volcanoes, Lava domes, Cryptodomes, Volcanic cones, Shield volcanoes and many more.
Another popular theory is the Hot Spot theory which also explains the formation of volcanoes. According to it there are various Hot spots situated beneath the earth surface and crust and are centers through which earth constantly spews out magma and other molten material and gases. Since the these hot spots are situated below the tectonic plates and volcanoes are on top of it, over the period of time the volcano drifts away from the point of hot spot and becomes inactive. This cycle continues and constantly makes new volcanoes. Yellow stone volcanoes are good examples of such scenarios.
References:
http://uk.danfossuniverse.com/page2120.aspx
http://science.howstuffworks.com/nature/natural-disasters/volcano2.htm
http://library.thinkquest.org/03oct/00795/volcano.html