Lava fountains can propel lava 1,000-2,000 feet (300-600 m) above the volcano.

The gas dissolved inside the magma is the driving force. As the magma approaches the surface the pressure on it decreases. The gas in the magma starts forming bubbles and the bubbles keep growing larger. The expanding and bursting bubbles force the lava into the air.

Left:  Lava Fountain at Kilauea Volcano. Image Credit: Steve Mattox, November 24, 1992.