ancient Romans, watching from the top of a mountain in the sky sees black smoke and fire, believed that before them the entrance to hell, or into the possession of Vulcan - god of fire and blacksmith.In honor of him, and called the fire-breathing mountains are still volcanoes.
In this article, we will understand, what is the structure of the volcano, and look into its crater.
active and extinct volcanoes on Earth
are many volcanoes like sleeping, and acting.Eruption of each of them can take days, months, and even years (for example, located on the Hawaiian archipelago Kilauea volcano woke up back in 1983 and still has his work does not stop).After that volcanic craters can freeze for several decades, then to remind myself a new release.
Although, of course, there are geological formations, which ended in the distant past.Many of them at the same time still retained a cone shape, but how exactly is their eruption, there is no information.These volcanoes are considered to be extinct.As example is Mount Elbrus and Kazbek, for a long time covered with glittering glaciers.And in the Crimea and the Trans-Baikal region are heavily eroded and destroyed by volcanoes, all lost their original shape.
What are volcanoes
Depending on the structure, activity and location, in geomorphology (the so-called science that studies described geological formations) allocated specific types of volcanoes.
In general terms, they are divided into two basic groups: linear and central.Of course, this division is very approximate, as most of them are linear tectonic fractures of the crust.
addition, even distinguish thyroid and domed structure of volcanoes, as well as so-called stratovolcanoes and cinder cones.As their activity is defined as the active, dormant or extinct, and at the location - both terrestrial and submarine subglacial.
How are volcanoes of the central linear
Linear (crack) volcanoes, as a rule, do not rise high above the ground - they have the form of cracks.The structure of the volcanoes of this type include long chutes associated with deep split the earth's crust, from which pours liquid magma, which has a basaltic composition.It spreads out in all directions and solidify, forming lava flows, erasing the forest, filling depressions, destroying rivers and villages.
In addition, during the explosion of the volcano on linear earth's surface can occur explosive pits having length of several tens of kilometers.In addition, the structure of volcanoes along the cracks decorate sloping shafts, lava fields, spraying wide and flat cones, radically changing the landscape.By the way, the main component of relief in Iceland - a lava plateau that emerged in this way.
If at the composition of the magma is more sour (high silica content), then around the mouth of the volcano extrusive grow (ie squeezed) shafts with loose structure.
structure of central volcanoes
central volcano - a cone-shaped geological formation that crowns the top crater - a depression or funnel-shaped bowl.It is, among other things, gradually moving up, as she grows volcanic edifice, and its size can be completely different and is measured in meters and kilometers.
volcanic craters are formed during an eruption may occur even on the slopes of volcanic mountains, in which case they are called parasitic or side.
Deep inside the mountain is volcanic crater on which rises up into the crater, the magma.Magma - a fiery molten mass has mostly silicate composition.It is born in the earth's crust, where her focus, and went upstairs in the form of lava poured out on the ground.
eruption, usually accompanied by the release of small splashes of magma that form the ashes and gases, which, interestingly, 98% of water.They are joined by various impurities in the form of flakes of volcanic ash and dust.
What determines the shape of volcanoes
form the volcano is largely dependent on the composition and viscosity of the magma.Flowing basaltic magma forms a shield (or thyroid) volcanoes.They usually have a flat shape, and a great circle.An example of representing these types of volcanoes, can serve as a geological formation, located in Hawaii and is known as Mauna Loa.
cinder cones - the most common type of volcano.They are formed during the eruption of large fragments of porous slag, which piled up, built around the crater of the cone, and they form a small part of the sloping hillsides.Such a volcano every eruption becomes higher.An example would be blown up in December 2012 in Kamchatka volcano Flat Tolbachik.
avilable domes and stratovolcanoes
and the famous Mount Etna, Mount Fuji and Mount Vesuvius - is an example of stratovolcanoes.They are called layered as they are formed periodically spewing lava (viscous and hardens quickly) and pyroclastic material, which is a mixture of hot gas, ash and red-hot stones.
As a result, these types of emissions, these volcanoes have sharp cone with concave slopes, which are alternated and these deposits.A lava flows are not only through the main crater, but from cracks, freezing at the same time on the slopes and ridge forming corridors that underpin this geological formation.
Dome volcanoes formed using a viscous granitic magma, which does not flow down the slopes, and solidifies at the top, forming a dome, which is like a cork, clog the mouth and knocked out Osprey under it over time gas.An example of this phenomenon may be a dome that formed over the volcano Mount St. Helens, in the north-west of the United States (it was formed in 1980).
What caldera
described above central volcanoes are usually conical.But sometimes during volcanic eruptions of the walls of the buildings descend, and thus formed the caldera - a huge depression that can reach depths of thousands of meters and a diameter of up to 16 km.From
discussed earlier, you remember that the structure includes a huge volcanic crater on which rises during the eruption of molten magma.When all the magma is top, inside the volcano there is a huge void.That's exactly it, and could fail the top of the wall and the volcanic mountains, forming the earth's surface bordered by remnants of the collapse of the vast kotloobraznye cavity with a relatively flat bottom.
The largest today is the Toba caldera on the island of Sumatra (Indonesia), and completely covered with water.Formed in such a way to the lake is very impressive dimensions: 100/30 km and a depth of 500 meters.
What are the fumaroles
volcanic craters, their slopes, foothills, and the crust of cooled lava flows are often covered with cracks or holes, of which the outsidepulled dissolved in the magma hot gases.They are called fumaroles.
Typically, large holes on clouds of thick white steam, because the magma is, as already mentioned, contains a lot of water.But besides it fumarole serve as a source for the emission of carbon dioxide, various oxides of sulfur, hydrogen sulfide, hydrogen halide, and other chemical compounds which can be very dangerous for man.
way, volcanologists believe that the members of the structure of volcanic fumaroles make it safer as the gases find a way out and do not accumulate in the bowels of the mountain, to form a bubble, which eventually eject lava to the surface.
Such volcano include the famous avachinsky, which is not far from Petropavlovsk-Kamchatsky.Smoke swirling over it, visible in clear weather for dozens of kilometers.
Volcanic bombs are also included in the structure of the Earth's volcanoes
If explodes long dormant volcano, when the eruption of its vents fly so-called volcanic bombs.They consist of fused rocks or debris solidified lava in the air and can weigh several tons.Its shape depends on what kind of lava composition.
For example, if the lava liquid and does not have time enough to cool down in the air - which fell to the ground turns into a volcanic bomb cake.A low-viscosity basaltic lava rotate in the air, taking account of this twisted form, or becomes like a spindle or a pear.Viscous same - andesite - chunks of lava are after the fall like bread crust (they are round or multi-faceted and covered with the network of cracks).
size diameter volcanic bombs can reach seven meters and found these formations on the slopes almost all volcanoes.
Types of volcanic eruptions
As pointed out in the book "Principles of Geology", which considers the structure and types of volcanic eruptions, Koronovskii NV, all kinds of volcanic edifices are formed by the various eruptions.Among them, especially distinguished 6 types.
- Hawaiian type of eruption - the release of a very liquid stock and lava that forms a huge shield volcanoes that lie flat.
- Stramboliansky type - release of more viscous lava that pushes the power of various explosions, resulting in formation of short powerful streams.
- Plinian type characterized by a sudden powerful explosions that accompanied the release of huge amounts of tephra (loose material) and the appearance of its streams.
- Peleysky type of eruption is accompanied by the formation of glowing avalanches and the burning clouds, as well as increase of extrusive dome of viscous lava.
- type of gas - only this eruption debris of older rocks, which is associated with the gases dissolved in the magma, or overheating within the structure of the volcano groundwater.
- eruption heat flow.It is similar to the release of high-temperature aerosol, consisting of pieces of pumice stone, minerals and volcanic glass oblomochkov surrounded by a shell of a hot gas.This eruption was widespread in the past, but in modern times there is no longer a people.
When were the most famous volcanoes
Years volcanoes can perhaps be attributed to the significant milestones in the history of mankind, because it's time to change the weather, perished huge number of people, and even erased from the Earth's entire civilization (as inthe eruption of a giant volcano destroyed the Minoan civilization in the 15th or 16th century. BC. e).
in 79 g of n.e.near Naples Vesuvius erupted, burying the seven-meter layer of ash of Pompeii, Herculaneum, Stabia and Oplonti, leading to the deaths of thousands of people.
In 1669 several eruptions of Mount Etna, as well as in 1766 - Mayon Volcano (Philippines) led to terrible destruction and death by lava flows thousands of people.
In 1783 the volcano Laki, exploded in Iceland has caused a decrease in temperature, which led in 1784 to the crop failure and famine in Europe.
A Tambora volcano on the island of Sumbawa, awakened in 1815 left the following year the entire Earth without a summer, lowering the temperature in the world at 2,5 ° C.
In 1991, the volcano with the Philippine island of Luzon their explosion temporarily dropped it, however, already at 0,5 ° C.
