Volcano

A volcano is a mountain formed from volcanic material in the earth’s crust. Molten rock, ashes, fragments, dust and gases are ejected from a vent in the central crater during an eruption.http://www.thefreedictionary.com/volcano An active volcano is one that is functioning or has the capability to do so, often generating seismic activity.http://www.allwords.com/word-active+volcano.html During an eruption gas is released and molten rock, known as magma, escapes from the Earth’s surface and is called lava. The explosiveness of the eruption depends on the amount of gas trapped in the magma and how easily the magma flows. A volcano that has not erupted for a long time but could in the future is called dormant. If a volcano has been dormant for more than 10,000 years it is considered extinct.http://www.ga.gov.au/hazards/volcano/

Volcanic activity is caused by the movement of the Earth’s tectonic plates, which also forms the type of volcano and influences its shape.http://www.ga.gov.au/hazards/volcano/causes.jsp Some volcanoes are a perfect peak, while others are deep depressions filled with water. How volcanoes function is reflected in their appearance. Three common volcanoes are the shield (dome-shaped, relatively slow-moving lava), composite (also known as strato and characterized by an explosive eruption style), and caldera (rare and the most dangerous, with eruptions so violent the volcano can collapse under its own weight). http://www.ga.gov.au/hazards/volcano/index.jsp

Volcanoes are usually located close to tectonic plate (massive rock slabs that make up the Earth’s surface) boundaries, with about 90% of all volcanoes on Earth existing within the Ring of Fire along the edges of the Pacific Ocean. About 1900 volcanoes are considered active, meaning there is some level of activity and they are likely to explode again.http://environment.nationalgeographic.com/environment/natural-disasters/volcano-profile/

A volcano’s eruptive history can give clues to predicting future eruptions, but this can be difficult because only a small number of the world’s volcanoes have a known history. Other indicators include earthquake activity – an eruption can be preceded by hundreds of small earthquakes known as earthquake swarms. Small changes, such as bulging in the shape of a volcano or emission of gas, can also indicate internal activity.http://www.ga.gov.au/hazards/volcano/causes.jsp

Large eruptions can be extremely dangerous for those living near a volcano. Searing lava, which can reach temperatures of 2000 degrees Fahrenheit (or 1250 degrees Celsius), is released and burns everything in its path during an eruption. Boulders of hardening lava rain down from the sky, as ash and toxic gases can cause lung damage and other problems with living creatures in the surrounding area.http://environment.nationalgeographic.com/environment/natural-disasters/volcano-profile/