Often volcanoes are formed at the junctions of tectonic plates of the earth. They can occur not only on land but also on the seabed, it is often formed Islands. In the oceans, thousands of Islands were formed by volcanic eruptions, the Azores, Hawaii, the Canary Islands, the Galapagos, and many others.
Volcanoes are extinct, sleeping, existing. Just on land, there are almost 1000 dead and asleep, 522 active volcanoes. The greatest number of volcanoes located in Indonesia, Japan, Central America, New Guinea, Chile, greater and lesser Sunda Islands of the Malay archipelago. On the territory of Russia volcanic hazard-prone residents of Kamchatka, the Kuril Islands, Sakhalin there are more than 70 active volcanoes.
People continue to settle near volcanoes. Currently dangerously close to active volcanoes is home to about 7% of the population. According to some, the eruption of volcanoes in the twentieth century killed more than 40 thousand people.
In places of magma and gases onto the surface of the earth formed one or more holes — craters. Often a crater is located on top of a volcano has a funnel or form.
Affecting factors of the volcano:
hot lava;
gases, smoke, steam, hot water;
ash, fragments of rocks;
the blast wave;
flows.
Lava escaped to the surface of the earth magma. The temperature of lava can reach up to 10,000°C or more. Lava forms lava flows with high flow, the rate of flow lava 100 km/h. Lava can flow for tens of kilometers from the volcano, affecting the hundreds of square kilometers.
During the eruption, volcanic ash and gases released into the atmosphere to a height of 15 — 20 km thick layer of ash can reach 10 m within a radius of 200 km from the volcano. If the pressure of the gases in magma are very high and she feels the resistance of the earth, the eruption is in the nature of the explosion. A characteristic feature of the volcanoes are re-eruption.
The decline in the number of human victims and material damage from volcanic eruptions is achieved by constant monitoring and forecasting of upcoming eruptions.
Protection from volcanic eruptions:
cooling lava with water.
the construction of artificial channels to divert lava flows and mudflows;
the construction of protective dams;
timely evacuation of people from dangerous zones.