And the fifth angel sounded, and I saw a star fall from heaven unto the earth: and to him was given the key of the bottomless pit. And he opened the bottomless pit; and there arose a smoke out of the pit, as the smoke of a great furnace; and the sun and the air were darkened by reason of the smoke of the pit.
Volcanoes form when chambers of magma, or hot molten rock, boil to the surface. These magma chambers often remain sealed for hundreds of years between eruptions, until the pressure builds sufficiently to break through a vent, which is a crack or weak spot in the rock above.
The lava released at convergent margins, combined with the high volatile content, can cause pressure to build in the volcano. This causes explosive eruptions. Eruptions tend to consist of large amounts of fragmented material released into the atmosphere.
A volcano can create a cloud of sulfuric acid that encircles the entire planet.