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A volcano is a mountain that has various components such as vents, holes, and craters. When the volcano erupts, lava, ash, cinders, dust, and hot gas pour out the top. Magma (when it’s under the ground) or lava (when it reaches the earth’s surface) is very hot it is a liquid rock. When the lava cools down, it turns into hard rock. The volcano also releases Ash, this is a gray powder that results from material being burned in the volcano. Ash can be carried in the air for many miles.
Volcanoes occur when the Earth’s plates pull apart causing magma to rise to the surface. Volcanoes can also occur over hotspots and where one plate dives beneath another, forcing magma to rise to the surface. Plates diving under one another is known as subduction.
As one goes deeper and deeper into the earth, there is increasing temperature with increasing depth. This is because radioactive elements deep within the earth are slowly disintegrating and producing heat. The rock in the earth insulates the heat, so that it accumulates and eventually liquefies the rock insulating it. Only slowly does this heat escape, which leads to the drastic differences of temperature with depth. This difference is referred to as the geothermal gradient. The average geothermal gradient is 2° to 3°C per 100 meters of depth, indicating that heat is flowing outward from inside the earth. Volcanoes are vents for the explosive escape of some of this heat. Magma is a general term referring to a mass of completely or partly molten rock containing the volatile that it acquired at its origin in the upper mantle of the earth. These volatile elements are gases either dissolved in the melt or as bubbles of gas that escape when the rock reaches the surface and solidifies. Volcanoes erupt because magma is less dense than the solid rocks surrounding it in the mantle of the earth. As it nears the surface, the volatile gases expand and boil out of the rock, and this force of explosion propels lava from the vent.
Ive got a few pictures of a volcano that will help you get a better idea of one:
With respect to the infomation, there are three different types of volvanoes wich
Shield volcanoes have gently sloping sides and are formed from layers of lava. Eruptions are typically non-explosive. Shield volcanoes produce fast flowing fluid lava that can flow for many miles. Examples of shield volcanoes include the Hawaiian volcanoes. Although these eruptions destroy property, death or injury to humans rarely occurs.
DOME( ACID LAVA CONES ):
Acid lava is much thicker than lava which flows from shield volcanoes. Dome volcanoes have much steeper sides than shield volcanoes. This is because the lava is thick and sticky. It cannot flow very far before ot cools and hardens. An example is Puy de Dome in the Auvergne region of France which last erupted over 1 million years ago.
Composite volcanoes, sometimes known as strato volcanoes, are steep sided cones formed from layers of ash and lava flows. Composite volcanoes can rise over 8000 feet. Examples of composite volcanoes include Mount Fuji (Japan), Mount St Helens (USA) and Mount Pinatube (Philippines).