How do volcanoes erupt?

A volcano is a natural opening in Earth’s crust through which lava (hot molten, or melted, rock), gases, steam, and ash escape, often in a big, noisy eruption or explosion. These eruptions are thought to act like safety valves, relieving the enormous heat and pressure that exist deep in Earth’s interior. A volcano is usually a cone-shaped mountain (its sides built up from solidified lava and ash) that has a hole or crater in its center through which it vents. There are several different kinds or stages of eruptions, many causing no damage to the places or people located near the volcano. But a few eruptions are huge and destructive. During these, lava can pour out and run down the volcano into surrounding areas, and enormous suffocating clouds of steam, ash, hot gases, and shooting rock can travel downhill at great speeds, covering many miles.