What causes volcanoes?
The Earth's crust is made out of humongous plates called 'Tectonic plates.' These plates move around a lot. They usually move past really slowly and smoothly. Sometimes, however, these plates crack and split, leaving a gap in the crust of the earth.
This allows the molten rock, or 'Magma', from the Earth's core to seeps through the gap. Aided with the gasses of the Earth, the magma erupts through the Earth's crust in a huge explosion. Rocks and ashes pour out too. Once the magma hits the air, it is no longer magma. The air caused a reaction which turned it into 'Lava.'
Over time, with every eruption, a mountain builds up, made from lava. A volcanic eruption is extremely dangerous and whole towns could get covered by the lava.
Volcanoes are formed when a vein of magma pushes its way towards the surface. After erupting repeatedly, the magma flows will eventually form a mountain of rock and cooled magma. The vein will extend all the way to the top of the mountain and branch out in all directions. At the base of the mountain, where it started, a magma chamber will form, fueling eruptions for the helicopter. Many volcanoes go dormant or completely die out because their magma chamber either cools or runs out. The drying of internal magma can leave behind interestingly shaped remains, after the volcano has collapsed.