A volcano is an opening in Earth's surface through which melted rock, hot gases, rock pieces, and ash burst forth, or erupt. When a volcano erupts, red-hot melted rock, poisonous gas, thick gray ash, and scorched rock pour or shoot out.Volcanoes come from the inside the Earth. Most volcanoes start 37 to 100 miles below the surface. There, it is so hot that rock melts. Melted rock below Earth's surface is called magma.
How A Volcano Forms
1: When rock melts, it lets out gases.
2: These gases mix with the magma.
3: The added makes the magma lighter than the solid rock around it.
4: Slowly, the gas-filled magma rises.
5: It is under great pressure from the weight of the surrounding rock.
6: Once near the surface, the gas and magma burst through a central opening, or vent.
7: The rock, ash, and other material builds up forming a volcano.
Three main kinds of material come out of volcanoes during an eruption. Most of the material is lava. Lava is the name for magma after it reaches the surface. Lava may be thin and flow fast. Or it may be thick and flow slowly. Flowing lava may be hotter than 1100*C. As lava cools, it gets hard. It forms into different shapes. Rock pieces may form when gas in sticky magma cannot escape. Pressure builds up until the gas blasts the magma apart. The pieces erupt into dust, ash, and large chunks called bombs. Gases also escape when a volcano erupts. Gases from volcanoes are mostly steam. But they often have harmful chemicals in them. These gases mix with ash to form a deadly black smoke.