Noting that a volcano is “an opening in the earth’s surface,” The World Book Encyclopedia explains: “Through this opening has come rock so hot that it is in a liquid or gaseous state. This melted rock deep in the earth is called magma.” It is thought that chambers of extremely hot magma are located twenty to forty miles below Earth’s surface. When magma presses against the roof of a chamber, gases are released. Upon reaching weak spots in the crust of the globe, these gases hollow out a passage, or “conduit,” that eventually reaches the surface.

When it gets to the surface of the earth, magma cools into “lava.” This escapes through an opening in the crust, spilling out over the edges of the volcano’s crater. “From time to time,” notes the reference work quoted above, “the opening becomes choked by cooling magma. This again causes gases to build up pressure to blast the plugging material into the air.”

When the lava escapes its high-pressure environment deep in the volcano and enters ordinary atmospheric pressure, exploding gases propel these particles sky-high, giving the appearance of shooting flames. The particles then cool off and solidify to form dense clouds of pumice, which settles over the countryside, ruining crops.

Volcanic gases consist mostly of steam. Carbon dioxide and nitrogen are sometimes major components. In smaller quantities these gases may include hydrochloric acid, hydrofluoric acid, sulfur, hydrogen sulfide, sulfur dioxide, hydrogen, and carbon monoxide. Interestingly, of these, only sulfur, hydrogen and carbon monoxide are combustible. These minor contributors, therefore, are responsible for the only true flames in volcanic eruptions.