Magma rises because it is lighter than the solid rock around it and is pushed upward by pressure and gases inside it.

Deep inside the Earth, rocks get so hot they melt, forming magma. This magma is less dense, or lighter, than the solid rocks nearby, so it tends to rise. Also, gases trapped inside the magma push it upward. Magma collects in chambers underground and builds up pressure. When this pressure becomes too strong, magma forces its way through cracks in the Earth's crust, leading to an eruption.