How does volcanic ash form

It forms when gas in stiff magma expand rapidly and the walls of the gas bubbles explode into any, glasslike slivers

Volcanic ash is form when explosive volcanic eruptions once the dissolved gases from the magma expand and are able to escape into the atmosphere. The force from all the gasses will then shatter the magma as well as the propels in to the atmosphere, then it will turn solid into fragments of volcanic rocks and glasses.