Most commonly, they are formed when an explosion tears apart the vent of the volcano, sending angular rock fragments flying through the air.
(an explosion; tears; apart; the vent of the volcano) (the volcano; sending; angular rock fragments flying through the air) (angular rock fragments; flying; through the air)
an explosion the volcano angular rock fragments
tears sending flying
apart the vent of the volcano
angular rock fragments flying through the air
through the air