Pumice rocks are formed due to the air that is trapped in
between the rocks, a body of magma spurting out with dissolved gas under
pressure. As the magma cracks through the Earth’s surface, the sudden pressure
drop causes the gas to come out of the solution. The flash of gas form the vent
slices the magma and blows it out as a molten lather. The lather hastily
solidifies as it flies into the air and falls back to Earth as pieces of
pumice.
