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: a volcanic cone composed of intermingled masses or alternate layers of lava and fragmental material.
Vent – An opening in Earth’s surface through which volcanic materials escape.
Main Vent: A volcano’s main vent is the weak point in the Earth’s crust where hot magma has been able to rise from the magma chamber and reach the surface.
A volcanic eruption occurs when hot materials from the Earth’s interior are thrown out of a volcano. Lava, rocks, dust, and gas compounds are some of these “ejecta”. Eruptions can come from side branches or from the top of the volcano.
The pyroclastic material erupted from an explosive volcanic eruption may be ejected as fragments, resulting in scoria cones or ash fall deposits, or it may spread outwards in ash flow deposits. This fragmental material is classified on the basis of grain size.
Stratovolcanoes show inter-layering of lava flows and pyroclastic material, which is why they are sometimes called composite volcanoes. Pyroclastic material can make up over 50% of the volume of a stratovolcano. Lavas and pyroclastics are usually andesitic to rhyolitic in composition.
Ninety-nine percent of the gas molecules emitted during a volcanic eruption are water vapor (H2O), carbon dioxide (CO2), and sulfur dioxide (SO2). The remaining one percent is comprised of small amounts of hydrogen sulfide, carbon monoxide, hydrogen chloride, hydrogen fluoride, and other minor gas species.
The rapid expansion of gas bubbles propels the magma and gas up the conduit. … Eventually, if the magma is “runny enough,” the gas bubbles escape easily; and instead of exploding, magma pours down the flanks of volcano as a lava flow.
The amount of dissolved gas in the magma provides the driving force for explosive eruptions. The viscosity of the magma, however, is also an important factor in determining whether an eruption will be explosive or nonexplosive.
Vocabulary Earth Science Chapter 9
|pyroclastic material||solid rock fragments that are ejected during a volcanic eruption|
|shield volcano||volcano with a broad base and gently sloping sides|
|viscosity||a substance’s resistance to flow|
|volcano||an opening in Earth’s crust through which molten rock, gases, and ash erupt|
Terms in this set (6)
During a volcanic eruption, the materials which come out or are ejected into the earth’s atmosphere and onto the earth’s surface are hot magma or lava, gases, steams, cinders, gaseous sulphur compounds, ash, and broken rock pieces. Lava bombs and pyroclastic material are also thrown out by a volcano when it erupts.
When corrected for voids in the lava and divided by the duration of the eruption, this yields a minimum eruption rate of about 50–200 cubic meters (13,000–53,000 gallons) per second. This eruption rate is significantly larger than most, if not all, known Kīlauea eruption rates.
Magmas with higher silica concentration are more viscous, and thus move slower than magmas with less silica. … More crystals in the magma enable more gas bubbles to form, and so they make an eruption more explosive. The rate at which pressure is reduced also affects the explosiveness.
What is pyroclastic material?
Ash makes up most of the pyroclastic material in an eruption. fragments of rock that are created by explosive volcanic eruptions.
Some of the most conspicuous and beautiful mountains in the world are composite volcanoes, including Mount Fuji in Japan, Mount Cotopaxi in Ecuador, Mount Shasta in California, Mount Hood in Oregon, and Mount St. Helens and Mount Rainier in Washington.
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