VOLCANOES
On Earth, volcanoes are generally found where
tectonic plates are
diverging or
converging. A
mid-oceanic ridge, for example the
Mid-Atlantic Ridge, has examples of volcanoes caused by
divergent tectonic plates pulling apart; the
Pacific Ring of Fire has examples of volcanoes caused by
convergent tectonic plates coming together. By contrast, volcanoes are not usually created where two tectonic plates slide past one another. Volcanoes can also form where there is stretching and thinning of the
Earth's crust in the interiors of plates, e.g., in the
East African Rift, the
Wells Gray-Clearwater volcanic field and the
Rio Grande Rift in North America. This type of volcanism falls under the umbrella of "Plate hypothesis" volcanism.
[1] Volcanism away from plate boundaries has also been explained as
mantle plumes. These so-called "
hotspots", for example Hawaii, are postulated to arise from upwelling
diapirs with magma from the
core–mantle boundary, 3,000 km deep in the Earth.
Erupting volcanoes can pose many hazards, not only in the immediate vicinity of the eruption. Volcanic ash can be a threat to aircraft, in particular those with
jet engines where ash particles can be melted by the high
operating temperature; the melted particles then adhere to the
turbine blades and alter their shape, disrupting the operation of the turbine. Large eruptions can affect temperature as ash and droplets of
sulfuric acid obscure the
sun and cool the Earth's lower atmosphere or
troposphere; however, they also absorb heat radiated up from the Earth, thereby warming the
stratosphere. Historically, so-called
volcanic winters have caused catastrophic
famines
- Volcanoes are formed by cracks or holes that poke through the earths crust, magma is pushes it way up through the cracks it is called volcanic eruption.
- the magma in the earth surface is called lava.
- the volcanoes do not just happen anyplace.
- when lava cools and hardens, it forms volcanis rocks
