Volcanic eruptions are geological phenomena characterized by the process of the emissions of hot debris, ash, outpouring of magma, which becomes lava after going out on the surface. Volcano eruption may have a time period ranging from several hours to many years.
Volcanoes are geological emergencies that can lead to disaster when damaging people life and properties, as well as harming plants, animals, etc.
Students who write their research paper on volcanic eruptions must know that there are three types of eruptions by their mechanism:
- The table eruptions are caused by the vaporization of water in contact with the magma, which ejects the enclosing materials.
- The phreato-magmatic eruptions are caused by the sudden cooling of magma by contact with water, which produces its fractionation and the explosive increase in the surface of the water-magma contact.
- The magmatic eruptions are caused by degassing the magma under the effect of decompression, which produces a decrease in density, which propels the magma upwards by the effect of buoyancy.
The duration of eruptions is highly variable: Some last a few hours, as the eruption of Vesuvius in 79; on some 1500 terrestrial volcanoes active, a little more than half does not exceed two months of activity and a little over a hundred lasts more than a year. There are usually 50-70 paroxysmal eruptions per year during an average of 15 days. The Puu Oo, one of eruptive vents of Kīlauea, has been erupting continuously since January 3, 1983.
Several categorizations of volcano eruptions have been proposed over time. At the beginning of XIXth century George Poulett Scrope distinguished paroxysmal, intermediate, and permanent eruptions. At the end of the XIXth century another system distinguished quiet, intermediate, and explosive eruptions. In 1908 Alfred Lacroix designed a classification to four types, Hawaiian, Strombolian, Plinian/vulcanian, Pelean, later enriched by the Icelandic type and solfatarien stage. It has evolved into several contemporary classifications.
This denomination by the names of volcanoes or regions should not lead to the believe that these volcanoes eruptions systematically correspond the type, or that a volcano is characterized by a single type of eruption. They simply reflect the fact that the description of the model was made from an eruption of the volcano or region. In reality, the changes which magma undergoes in the magma chamber lead to changes in both duration of the volcano life and that of the eruptive cycle. Cooling magma chamber ceiling causes a fractional crystallization of the liquid phase, the first crystals to form minerals are basic, heavier, which settle to the bottom of the chamber and leave the summit magma enriched in silica, it called magma differentiation.
In addition, over long periods, the magma tends to partially dissolve rocks. For continental volcanoes it is usually mineral felsic crust which will again enrich the magma in silica. In this case, the more the volcano is aged, the more its lava will be viscous and its eruptions explosive. There are exceptions: if the magma chamber is located in calcareous sediments, as in the case of Vesuvius, the magma becomes more basic and eruptions less explosive.
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