How do volcanoes erupt?

You ask: How volcano erupt?

Deep under ground, rock so hot it melt to goo — ten times hotter than boiling water. Caveman call it fire-goo. Fire-goo lighter than hard rock around it, so it push up, up, slow. Inside goo hide gas, squished tight like breath Caveman hold in chest. As goo rise, the squeeze let go — gas make bubbles, bubbles want out. Pressure build behind rock lid up top. When push get stronger than lid, lid break! Goo, gas, ash blast into sky. Runny goo make river of fire. Thick goo trap more gas, so it blow big and throw rock far. Cave wisdom: volcano not angry mountain — just hot goo and trapped breath clawing their way out.