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.
An volcanic eruption is a place where hot melted rock called magma rises from deep inside the earth and erupts as lava out of the earth's crust. The world has three main types of volcanoes: Shield, Cinder, and Composite. The volcanoes in the Hawaiian Islands are Shield type volcanoes with long gentle slopes.fter many thousands of eruptions over a long period of time, the volcano mountains eventually grow to rise above the ocean to become islands. This is how the Hawaiian Islands were made. Here is a diagram of recent lava flows from the Kilauea volcano on the Big Island on February 4, 2011.