Phenocrysts are crystals that are larger than the matrix and are identifiable with the unaided eye. Rhomb porphyry is an example with large rhomb shaped phenocrysts embedded in a very fine grained matrix. Volcanic rocks often have a vesicular texture caused by voids left by volatiles trapped in the molten lava.
A Vulcanian eruption is a short, violent, relatively small explosion of viscous magma (usually andesite, dacite, or rhyolite). This type of eruption results from the fragmentation and explosion of a plug of lava in a volcanic conduit, or from the rupture of a lava dome (viscous lava that piles up over a vent).ere are some of the most common types of eruptions: In a Hawaiian eruption, fluid basaltic lava is thrown into the air in jets from a vent or line of vents (a fissure) at the summit or on the flank of a volcano.
Volcanic eruption and Volcanic eruptions redirect here. For the short story, see Volcanic Eruption. For the film company, see Volcanic Eruptions. Some of the eruptive structures formed during volcanic activity: a Plinian eruption column, Hawaiian pahoehoe flows, and a lava arc from a Strombolian eruption.