A volcano can be defined as a fissure in the crust of the earth erupting gases and molten lava. Volcano is a vent through which magma and dissolved gases are discharged. Magma forms when lower crust or the upper mantle of the earth melts and this magma is discharged in volcanic eruption.
Volcanic eruption is caused by three major factors. The first is buoyancy of the magma formed in the crust of the earth. When rocks melt in the crust of the earth forming magma, its mass remains the same, whereas the volume increases considerably. This magma rises towards the surface due to its buoyancy. The second factor is the pressure from the gases in the magma. Molten lava produces gases such as sulphur dioxide and carbon dioxide. As the magma rises to the surface, pressure from the gases within it increases resulting in volcanic eruption
The third factor causing a volcanic eruption is the injection of a new mass of magma into an already filled magma chamber. When a high volume of new magma enters an already filled magma chamber, the resulting high pressure creates a volcanic eruption.
Volcanoes erupt because of the structure of the planet Earth. We walk about on the hard crust that exists on the surface of the planet. Some of the crust is covered by water but some is dry land. Underneath the crust are four more layers. The first layer is hard with pockets of melted rock. The temperature is much hotter here than on the crust.
Going down deeper still to the next layer, the temperature is hotter still. The second layer is the mantle. The mantle is solid hot rock that is between 900 and 3000 degrees Celsius – 90 to 300 times hotter than a boiling kettle.
The third layer is called the outer core and is liquid metal that is between 3000 and 4000 degrees Celsius. The inner core is solid metal but is the hottest of all – between 3000 and 6500 degrees Celsius.
Volcanoes form when melted rock that forms in pockets under the Earth's crust bursts out to the surface. Tons of rock that was under the surface can be released and can flow out of the volcano or can explode from it.
Volcano's are caused by the friction of the earths plates moving and crashing into each other. This collision is refereed to as plate tectonics. The Earths surface is actual a series of plates that are continually growing and moving. When the plates contact with an opposing plate the forces of the immovable object and the impregnable force exists. Since something has to give the plate with the stronger or larger and more able capacity forces the weaker plate underneath. The results are major friction, power and force. This force and power is accumulated in areas know as volcano's and when the cavities and forces reach a point that it is no longer containable the eruptions are seen in the form of a volcanic eruption. This eruption reduces the built-up stress, heat and pressure generated by the collision of the earths plates.
Inside the earth's mantle there is red ot liquid rock, called magma. Volcanoes erupt when magma rises to the surface of the Earth, which causes bubbles of gas to appear. The gas can cause pressure to build up in the mountain and it eventually explodes (or erupts). When the magma erupts out of the volcano then it is called lava! Easy peasy and I'm only in year 9!
There are three different types of volcano, which are active, dormant and extinct. For active volcanoes, it will have constant emission of lava, ash, dust and smoke, and also has a strong sulfur smell. For dormant volcanoes, it has not erupted for hundreds of years, but may erupt in the future. For extinct volcanoes, it has no record of eruption in recorded history and it has no sign of possible eruption.
Lava flow can be classified according to its viscosity. This refers to the resistance of a substance to flow. For example, water has low viscosity so it flows easily. Honey, on the other hand, has higher viscosity and so it flows slowly. Viscosity is an important factor in determining the type of volcanic eruption that would occur, as a result affecting the shape or type of volcano that would be formed. The viscosity of lava is dependent on two factors- the amount of silica it contains and its temperature. The higher the content of silica, the higher the viscosity of the lava. The lower the temperature, the higher the viscosity. There are generally two types of lava with different viscosity- basic lava and acidic lava. Basic lava, which is less viscous, is very fluid. It spreads easily over an area and also generates less powerful explosions as gases trapped within the lava are readily released. It creates volcanoes with gentler slopes. Acidic lava, on the other hand, is more viscous and so it flows more slowly and produces greater explosions as the gases trapped within the lava are not readily released, contributing to the formation of taller and steeper volcanoes.
It is the movement of tectonic plates that is the prime reason for the eruption of volcanoes. The movement either can be pulling apart or coming together and there are a few examples of both kinds of eruptions. Though the movement cases the eruption, it does not happen exactly at the place where the movement happens, it happens where the earth crust is quite thin.
The places where volcanoes occur are called hotspots and Hawaiian Islands are the prime example of this kind of volcanoes. One interesting fact about volcanoes is that they are not only present on the planet earth but can be found in some other planets also and some rocky planets and moon are the prime examples where you can find volcanoes.
When rock inside the Earth becomes hot enough it melts. This molten rock, or magma, is less dense than the surrounding solid rock. Just as an object that is less dense than water will float on water, the relatively low density of the magma causes it to rise to the surface of the Earth. If the magma contains water and dissolved gasses, when the magma reaches the surface the water and dissolved gasses will suddenly expand into steam and gas, causing a violent eruption. This is like shaking a coke can and then popping the tab.
It is caused by the built up of hot magma that leads to the pressure inside the volcano to shoot up tremendously and so the volcano erupts, spewing up tons and tons of lava.
A volcanic eruption only takes place when the hot rising magma deep down in the volcano wants to be free. In the Mount St Helens volcano, pressure would have started building up around March. This was indicated by the abrupt increase in earthquakes and the plumes of ash rising from the volcano. This was a definite signal to scientists that the volcano had come back to life. Because of the build up in pressure the magma was pushing and breaking the rock in the magma chamber to get to the surface. This is because of the magma being less dense than the surrounding rock and the increasing pressure from expanding gases. In the case of the Mount St Helens volcano the magma could not escape through the main vent because of unbreakable volcanic rock hardened by previous eruptions; and veered off in a dike. A dike is where the magma takes a different path to the surface. This dike grew into crypto dome (a chamber just beneath the surface). This chamber grew at an estimated 1.8m per day due to the increasing pressure. The rock 'lid'; the only thing stopping magma breaking the surface; was being crushed by the magma.
Volcanoes can be active, dormant or extinct. An active or dormant volcano can erupt. There are essentially two major types of eruptions. If there is a magma buildup within the volcano, then it will move upwards trying to find a way out of the enclosed mountain. The magma is propelled upwards by various gases; this finally culminates in an eruption. The silica content will determine the viscosity of the lava. Another type of eruption occurs when there are obstacles in the pipe of the volcano. This happens due to a high amount of pumice in the rocks. Eruptions of this kind are generally more violent.
The rate at which lave will flow out of a volcano will depend on the type of eruption, there have been cases documented where lava has flowed at a rate of 100 kilometers per hour. Along with lava there are stones and rocks that form part of the eruption.
Eruptions is where the outer crust on the Earth cracks and all magma and hot gas escape through the crack, through the volcano, and spurts out all over the country, and affects most, if not all, the world.
Near subduction zones one plate is forced below another plate. This is caused by compressional forces. The rock is melted by the hot mantel and it is turned into magma. This magma then flows into cracks and fractures. The magma may reach the surface or it may cool to form intrusive rocks. Volcanoes are opening where the magma, gases and ash erupt. The hole is called a vent.
A volcano could erupt when the tectonic plates rub together OR when new magma is ready to be pushed into the magma chamber which forces the old ones to spurt out the top to make room for the new ones.
