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What are volcanos? There is quite a lot to know about volcanos and here is a starting point. According to an explanation in the Wikipedia volcanos portal:
A volcano is an opening, or rupture, in a planet’s surface or crust, which allows hot, molten rock, ash, and gases to escape from below the surface. Violent explosive eruptions from such vents often produce craters or calderas and coat extensive areas in volcanic ash, while the lava from comparatively gentle effusive eruptions may eventually form large plains, cones or mountains.
Volcanoes are generally found where tectonic plates are pulled apart or come together. A mid-oceanic ridge, such as the Mid-Atlantic Ridge, hosts volcanoes caused by divergent tectonic plates pulling apart; the Pacific Ring of Fire contains many volcanoes caused by convergent tectonic plates coming together. By contrast, volcanoes are not commonly created at transform boundaries, where two tectonic plates slide past one another.
We found a great playlist on National Geographic Kids about volcanos:
SciShow Kids also has a great video about volcanos for kids:
While we were looking up volcano information on Wikipedia, we saw some great explainer images. This one shows the anatomy of a volcano:

We also found this great view of an erupting volcano from the perspective of a satellite passing overhead:
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Volcano eruptions can be pretty dangerous for aircraft too. You may remember the 2010 eruption of the Eyjafjallajökull volcano. National Geographic has an interesting report on the dangers of volcanic ash titled “Volcanic Ash Stops Europe Flights—Why Ash Is Dangerous“.