Outside our planet is covered with solid and cold earth crust. But deeply in it there is a heated liquid kernel consisting of magma. The processes happening in the planet create huge pressure. Through breaks in earth crust magma, less dense, than strong breeds, together with the gases dissolved in it comes to light. The volcanoes growing in process of the next eruptions are so formed.
Volcanoes are located in those places of the planet where there are breaks in earth crust, at edges of earth's plates, especially, where a part of one plate lies on another. Many volcanoes are located at an ocean floor. Often sea water, getting to a muzzle, provokes the following explosion. When the cooled-down lava rises over water level, the whole islands are formed of magmatic breeds. The Hawaiian Islands can be such example.
Volcanoes divide into acting, fallen asleep and gone out. The first constantly produce gases, a lava and ashes from a muzzle. Natural disaster can occur at any time. The fallen asleep volcanoes actively do not allocate eruption products, but it in principle can happen. Often muzzles of such volcanoes are filled with the cooled-down lava. It is difficult to punch this lava stopper even the strongest stream of magma and gases. But if it occurs, then eruption of huge scales begins. As, for example, a volcano of Krakatau on the mountain Elena's Saint in 1883 caused the most powerful natural disaster. Echoes of this incident were observed on all globe.
Extinct volcanoes are not thrown up for tens and hundreds of years. But it is impossible to guarantee that they will not start the destroying activity over again. So happened to a volcano Anonymous in 1955 - 1956 years. It did not function more than nine hundred years and was considered as extinct, woke up in 1955, and all ended with explosion in 1956. But if in magma of a few dissolved gases and on its way there are no obstacles, eruption takes place rather quietly, and lava lakes are formed. At a dense lava the volcano looks konusoobrazno, often has several craters – openings through which magma comes to light. If in a crater water gets, then she jumps out back in the form of a geyser – a stream of hot water and volcanic particles. Except a lava and gases from a volcano muzzle the huge cloud of ashes closing the sun on many kilometers around often takes off.