DEFINATION AND CHARACTERISTICS

Volcanic eruptions happen when lava and gas are discharged from a volcanic vent. The most common consequences of this are population movements as large numbers of people are often forced to flee the moving lava flow. Volcanic eruptions often cause temporary food shortages and volcanic ash landslides called Lahar.

The most dangerous type of volcanic eruption is referred to as a 'glowing avalanche'. This is when freshly erupted magma forms hot pyroclastic flow which have temperatures of up to 1,200 degrees. The pyroclastic flow is formed from rock fragments following a volcanic explosion , the flow surges down the flanks of the volcano at speeds of up to several hundred kilometres per hour, to distances often up to 10km and occasionally as far as 40 km from the original disaster site.

How are Volcanoes a Result of Plate Tectonics?

Earth is made of four concentric layers - inner core, outer core, mantle, and crust. Outermost layer is the crust, on which we live. This layer is actually made up of seven major tectonic plates. These plates float on the mantle - a semi-solid layer made of molten rock, which we call magma. Convection currents are formed in the mantle as a result of radioactive decay in the Earth's crust. These currents cause the plates in the crust to either move towards each other, away from each other or slide past each other. This movement of plates is called plate tectonics.

Formation of Volcanoes through Convergence

A convergent or destructive boundary is where two plates (usually a continental and oceanic) move toward each other, forcing the denser (oceanic) plate to go under the lighter (continental) plate and sink into the mantle. This is called subduction, and the place where this happens is the subduction zone. When water and rocks from the denser, subjugating plate, come in contact with the hot mantle, they transform into magma. This magma, due to the various gases present, is lighter than the surrounding material and might break through faults in the crust in an violent explosion. These volcanic eruptions are violent and can cause immense damage to all living things in their proximity. Mt. Fuji, in Japan is a volcano found at convergent boundary.

Formation of Volcanoes through Divergence

Divergence is another cause of volcano formation. At a divergent or constructive boundary, two plates diverge i.e. they move away from each other, forming a gap between them. Hot magma rises from the mantle to fill this gap, cools on the surface and forms a new crust of igneous rock. This type of lava flow, though accompanied by earthquakes, is mostly placid, and usually occurs on the ocean bed. These type of eruptions can continue for years resulting in the formation of oceanic ridges like the mid-Atlantic ridge. The ridges can break the surface of water to form volcanic islands. Iceland, world's second largest volcanic island, is a part of mid-Atlantic oceanic ridge.

What Causes a Volcano to Erupt?

Volcanic eruptions and earthquakes are a way for Earth to release pressure and heat, much like a safety valve. There are three dominating theories to explain what causes a volcano to erupt -

Due to Density-difference in Magma

As per the first theory, due to heat and pressure in the Earth's mantle, solid rocks melt, to form magma. Magma has the same mass as the solid rock, but more volume, making it lighter and more buoyant. So, it will attempt to rise, if this magma continues to encounter high-density material till it reaches the Earth's crust, volcanic eruption occurs. It can either be in the form of a lava-flow or may be explosive.

Pressure of Released Gases

According to the second theory, magma contains dissolved substances such as water, sulfur dioxide and carbon dioxide. The solubility of magma decreases with the decrease in pressure as it rises up towards the crust, and the gases get released in the form of bubbles. When the volume of the gas bubbles in magma reaches around 75%, magma disintegrates into pyroclasts, a mixture of partially molten and solid fragments. The bursting of pyroclasts is very explosive and the cause of some of the most violent eruptions on the surface of Earth.

Injection of New Magma

The third theory says that when new magma enters a chamber already brimming with magma, the volcano erupts due to the additional pressure exerted by the injection of new magma. This type of eruption can be placid or violent.

The intensity of eruption usually depends on the viscosity of magma and its gas content. High-viscosity magma usually results in bigger, more intense eruptions, whereas magma that flows easily will have lower pressure build-up, so a less violent eruption. Highly viscous magma is characterized by the presence of more silicates and contains less dissolved water. Another important factor is the amount of gases present in the magma. Magma containing large amount of trapped gases will lead to a violent eruption, and less gases in magma will result in an effusive flow.

EFFECTS OF A VOLCANO

The problems caused by volcanoes are earthquakes,tsunami and mudslides. Mudslides happen in California. Environmental effects caused by the volcanoes can kill crops and animals that are near to it's location the ash falls that spread when a volcanoe errupts may harm not only the environment but also the humans as well. environmental problems consist such as mudslide,tsunami,earthquakes,floods,drought and death to people,animals and plants.Volcanoes can also cause distructon of buildings,roads but they also bring minerals like gold,silver,iron,etc.