The word volcano is derived from the name of Vulcano, a volcanic island
in the Aeolian Islands of Italy whose name in turn comes from Vulcan,
the god of fire in Roman mythology.
The study of volcanoes is called volcanology, sometimes spelled vulcanology.
"A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. Earth's volcanoes occur because its crust is broken into 17 major, rigid tectonic plates that float on a hotter, softer layer in its mantle. Therefore, on Earth, volcanoes are generally found where tectonic plates are diverging or converging, and most are found underwater. For example, a mid-oceanic ridge, such as the Mid-Atlantic Ridge, has volcanoes caused by divergent tectonic plates whereas the Pacific Ring of Fire has volcanoes caused by convergent tectonic plates. Volcanoes can also form where there is stretching and thinning of the crust's plates, e.g., in the East African Rift and the Wells Gray-Clearwater volcanic field and Rio Grande Rift in North America. This type of volcanism falls under the umbrella of "plate hypothesis" volcanism. Volcanism away from plate boundaries has also been explained as mantle plumes. These so-called "hotspots", for example Hawaii, are postulated to arise from upwelling diapirs with magma from the core–mantle boundary, 3,000 km deep in the Earth. Volcanoes are usually not created where two tectonic plates slide past one another. Erupting volcanoes can pose many hazards, not only in the immediate vicinity of the eruption. One such hazard is that volcanic ash can be a threat to aircraft, in particular those with jet engines where ash particles can be melted by the high operating temperature; the melted particles then adhere to the turbine blades and alter their shape, disrupting the operation of the turbine. Large eruptions can affect temperature as ash and droplets of sulfuric acid obscure the sun and cool the Earth's lower atmosphere (or troposphere); however, they also absorb heat radiated from the Earth, thereby warming the upper atmosphere (or stratosphere). Historically, volcanic winters have caused catastrophic famines." -www.wikipedia.org
www.wikipedia.org
In mineralogy, an inclusion is any material that is trapped inside a mineral during its formation. Generally there are two distinct groups of inclusions:
-Inclusions of the forming environments
-Inclusions of xenomorphing material
www.wikipedia.org
Inclusions of melt and fluids are inclusions of formig environments. These inclusion might be mono- or -polyphasic. Melt inclusions are always a solid glass at surface conditions. Other phases might have a genetic relation to the melt or fluid in inclusions, or they might be xenogenic. In list of other phases are gas (picture 1. a) or crystals in this glass (picture 1. b). Also different combinations of these phases are possible
As inclusions of xenogenic materials, crystalls can contain crystals, gas, anoter fluid or melt, fragments or rocks, petroleum or even insects.
I`ve written a diploma paper to get my bachelor`s degree. This research paper is about huge explosive caldera eruption which occurred about 20.000 years ago on Iturup Island (South Kuril Island). The volume of erupted rock during one session was about 100.000 km3.
I had samples that were taken moving up cross section of pumice-pyroclastic rocks. Even though bulk composition analyses represent that pumices has dacite composition, the composition of glass in melt inclusions corresponded to rhyolite and high-T minerals such as pyroxenes have mg#50-60. Water content in melt was 4-6 wt. %.
The main aim of my research was to explore reasons and P,T,X conditions of formation this uncommon mineral`s association and formation of high-silica melts which cause huge catastrophic eruptions.
Dependence of FeO on Fe(tot) in pyroxen`s phenocrysts.
Data: EDS and WDS EPMA
X-axis:MgO, wt%; Y-axis: FeO+Fe2O3, wt%.
The Kuril Islands form part of the ring of tectonic instability encircling the Pacific Ocean referred to as the Ring of Fire. The islands themselves are summits of stratovolcanoes that are a direct result of the subduction of the Pacific Plate under the Okhotsk Plate, which forms the Kuril Trench some 200 kilometres (120 mi) east of the islands. The chain has around 100 volcanoes, some 40 of which are active, and many hot springs and fumaroles.
The chain ranges from temperate to sub-Arctic climate types, and the vegetative cover consequently ranges from tundra in the north to dense spruce and larch forests on the larger southern islands. The highest elevations on the islands are Alaid volcano (highest point: 2,339 m or 7,674 ft) on Atlasov Island at the northern end of the chain and Tyatya volcano (1,819 m or 5,968 ft) on Kunashir Island at the southern end.
Landscape types and habitats on the islands include many kinds of beach and rocky shores, cliffs, wide rivers and fast gravelly streams, forests, grasslands, alpine tundra, crater lakes and peat bogs. The soils are generally productive, owing to the periodic influxes of volcanic ash and, in certain places, owing to significant enrichment by seabird guano. However, many of the steep, unconsolidated slopes are susceptible to landslides and newer volcanic activity can entirely denude a landscape. Only the southernmost island has large areas covered by trees, while more northerly islands have no trees, or spotty tree cover.
Fractional crystallization, or crystal fractionation, is one of the most important geochemical and physical processes operating within the Earth's crust and mantle. Fractional crystallization is the removal and segregation from a melt of mineral precipitates; except in special cases, removal of the crystals changes the composition of the magma. In essence, fractional crystallization is the removal of early formed crystals from an originally homogeneous magma (for example, by gravity settling) so that these crystals are prevented from further reaction with the residual melt. The composition of the remaining melt becomes relatively depleted in some components and enriched in others, resulting in the precipitation of a sequence of different minerals. ©Wikipedia.org
Generally, this process is based on difference in density of crystals and magma. For example, olivine is a one of early formed minerals and it has greater density than surrounding magma. This model illustrates this process.
The size of polygons on the screen continuously increases representing crystal growth (it does not depend on any real equation). There are 2 forces that acting on crystals concerning in this model.
F=mg (where "m" is mass and "g" is a gravity of the Earth) is a gravity force; the mass of crystalls calculating as m=rho/v (where "rho" is a density of crystalls and "V" is a volume of crystalls, as a simplification the Volume is calculated as a volume of sphere V=4/3*Pi*R^2. This force acting downside to the crystalls
The second force is F=rho*g*V that has opposite direction with the force of gravity ("rho" here is a density of the magma and is not calculated; "g" equal 9.8; "V" is a volume which is calculated the same way as it described above).
The speed of settling is depend on radius that is affects crystal`s mass; density of crystalls and density of liquid.
Velocity of crystalls fall is V=a*t , as an initial velocity equal 0("V" is a speed; "t" is time)where "a" is calculated from
Using Newton`s second law: (F(gravity)-F(buoyance))/m=a,
g=9.8 (Earth conditions)
Example: There are 3 sliders that control "rate of growth" for each of minerals. Used density of crystals is 3320 kg/m^3 that is a density of #50Fo Olivine; preset density for liquid is 2850 kg/m^3 (density of basaltic magma); 2700 kg/m^3 is density for high-Ca plagioclase; 3300 kg/m^3 is a density of Ca-pyroxene.
If the density of Crystalls is greater than density of melt, concerning Earth conditions (g=9.8 m/s^2), crystalls move down and settle on the bottom, if not-crystalls move upward. These factc are correct as we can see in nature.
If we increase the difference between densities (increase the density of crystalls and decrease the density of melt), the velocity should be increased. This is how it happens in this model. As a conclusion, we can confirm that this model works correctly
Of course a lot of additional factors must be conserned in this model, but in fact, this model most likely can be used for explanation the process of fractional crystallization to young geologists, so i suppose that for this purposes it is enough.