A volcano is a mountain that opens downward to a pool of molten rock below the surface of the earth. Unlike most mountains, which are pushed up from below, volcanoes are vents through which molten rock escapes to the earth's surface.
Volcanoes are formed when magma from within the Earth's upper mantle works its way to the surface. At the surface, it erupts to form lava flows and ash deposits. Over time as the volcano continues to erupt, it will get bigger and bigger.
Why do Volcanoes Erupt?
Beneath the Earth’s crust the rocks, melted by heat, form magma, a gleaming hot liquid mass. When the magma rises up from the depths of the Earth towards the surface, it escapes through a volcano, and there is an eruption. From the mouth of volcano there escapes a flow of lava, often together with steam, cinders, dust and lava fragments.
When the lava spurts out from the crater (mouth) of volcano, it is red and very, hot (1100degree) and destroys everything it comes in contact with. As it flows the lava cools slowly and solidifies around the volcano, becoming grey or black in colour.
When do Volcanoes Erupt?
Active volcanoes erupt constantly or periodically. Dormant volcanoes have long periods without eruption. In extinct or ‘dead’ volcanoes the magma in the volcano reservoir is exhausted, or it is absorbed into the Earth’s crust.
Different shapes of volcanoes.
The shape of the volcano depends on the chemical composition of the lava and the way in which it pours out.
If the lava is thicker, it solidifies more rapidly, and the volcano is cone shaped with steep sides. The thickest type of lava solidifies immediately without flowing down. This forms steeple like volcanoes up to 300m high.
When the lava is very fluid, it flows for a long time before solidifying and forming dome shaped volcanoes which are low and wide.
Linear volcanoes with long, thin, cracks open up on the ocean beds. The magma escapes the beds slowly and solidifies on the bed without creating any changes in the appearance of the Earth.
The intensity of volcanic eruption is measured by the quantity of cinders and ash scattered into the air.