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.
Geophysical hazards: volcanic eruptions. Definition and characteristics. Volcanic eruptions happen when lava and gas are discharged from a volcanic vent. The most common consequences of this are population movements as large numbers of people are often forced to flee the moving lava flow.Volcanic eruptions often cause temporary food shortages and volcanic ash landslides called Lahar.The most dangerous type of volcanic eruption is referred to as a 'glowing avalanche'. This is when freshly erupted magma forms hot pyroclastic flow which have temperatures of up to 1,200 degrees.he most common consequences of this are population movements as large numbers of people are often forced to flee the moving lava flow. Volcanic eruptions often cause temporary food shortages and volcanic ash landslides called Lahar. The most dangerous type of volcanic eruption is referred to as a 'glowing avalanche'.