According to the Global Volcanism Program at the Smithsonian Institution, as of December 2014, there have been a little over 400 confirmed eruptions in the world since January 2004. These eruptions range on the Volcanic Explosivity Index, or VEI, from 0 up to 5. A VEI of 0 to 1 is very small, while 5 is classified as very large.
Many volcanoes erupt every day, all over the world. Some are very small and have little to no effect on the surrounding environment. The degree and danger of the volcano's explosiveness is in direct relation to the amount of gas trapped in its magma and how easily the magma can flow out of the volcano.
There are three basic types of volcanoes:
- Shield volcano - a shield volcano does not have the familiar cone shape, but rather is flat with a dome-like shape. The eruptions are usually gentle and humans can outrun or sometimes even outwalk the lava flow.
- Composite volcano - these volcanoes have the familiar cone shape and explosive eruption style. The magma explodes violently, causing clouds of dangerous volcanic ash.
- Caldera volcano - while these volcanoes are the most explosive, they do not have the familiar conical shape. Instead, this type of volcano is a circular, basin-shaped depression in the earth. This is because the eruptions are so forceful, the chambers within the volcano are left empty, causing it to collapse into itself.