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.
Volcano Facts Find out more volcano facts about these mountains of fire that produce Earth eruptions that can alter the weather on our planet sometimes for several years. Kids Fun Science The links on our home page include information about volcanoes, science activities, plate tectonics, the rock cycle and much more.he dome on Mount Saint Helens has been growing since the 1980 eruption in the caldera formed during the eruption. Volcanic eruptions. Check out volcano facts about volcanoes that have erupted worldwide on these web pages: 79 AD Vesuvius eruption, Alaskan volcanoes ,and the Krakatoa eruption.