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.
The Top 5 Deadliest Volcanic Eruptions. Sources: Top 5 of Anything Research, U.S. Geological Survey. List Notes: All deaths are estimated as exact statistics are difficult to find. High estimate death tolls shown here often include the secondary after-effects of disastrous events such as disease & famine. Prehistoric volcanic eruptions are thought by experts to have caused many more deaths on this planet, however reliable data is missing on these events and thus they are not included here.