Volcanoes

Hypothetical sections of the structure of some types of volcanoes and their roots.

V. are divided into those acting, that fell asleep and extinct. The first include: V., izvergayushchiyesya in real, time is constant or periodically; V., about the eruptions of which exist true given; V., about the eruptions of which there is no information, but which separate hot gases and waters (sol'fatarnaya stage). To those fallen asleep carry v., about the eruptions of which there is no information, but they preserved their form and local earthquakes occur under them. Extinct NAZ strongly destroyed and washed away v. without any manifestations of vulkanich. of activity.

Depending on the form of feeders v. they divide into the central and the interstitial.

Deep of magmatich. centers can be located into the top, the mantles to glub. on the order of 50-70 km (V. klyuchevskaya sopk in Kamchatka Kilauea on Hawaiian about- VAKh) or in the earth's crust to glub. 5-6 km (V. vezuviy, Italy) are deeper.

Volcanic phenomena. Eruptions are prolonged (during several years, decades and centuries) and short-term (measured by hours). To the forerunners of eruption relate vulkanich. of earthquake, akustich. phenomenon, change in the magnetic properties and composition of fumarole gases and other phenomenon. Eruption usually begins with strengthening the ejections of gases first together with the dark, cold fragments of lavas, and then with those incandesced. These ejections in the some cases are accompanied by the effusion of lava. The height of the lift of gases, it is water vapor, saturated by ashes and fragments of lavas, depending on explosive force, it kolebletsya from 1 to 5 km (during the eruption Of v. bezymyanny in Kamchatka into 1956 it it reached 45 km). The rejected material is transferred to the distances from several. to tens of thousand. km. The volume of the rejected fragmental material now and then reaches several. km³. With the some eruptions the concentration of vulkanich. of ashes in the atmosphere is such large that appears the darkness, similar to the darkness in the closed accomodation. This occurred into 1956 into pos. Keys, 40 km V. bezymyanny. Eruption is the alternation of weak and strong explosions and effusions of lavas. Explosions max, force NAZ of kul'minats. of paroksiz m. The decrease of explosive force and the gradual curtailment of eruptions occurs after them. Volumes of the discharged lava to tens of km³.

Types of eruptions. Eruptions v. are not always identical. Depending on quantities, relationships of izvergayemykh vulkanich. of products (gaseous, liquid and solid) and of viscosity of lavas are isolated 4 main types of the eruptions: effusive, mixed, extrusive and plosive, or as their is more frequent NAZ, respectively - Hawaiian, strombolianskiy, domelike and vulkanskiy. The Hawaiian type of eruption, which creates most frequently thyroid volcanoes, is characterized by the relatively calm effusion of the liquid (basaltic) lava, which forms molten lakes and lava flows in the craters. The gases, which are contained in a small quantity, form the fountains, which eject lumps and drops of the liquid lava, which are drawn out in flight into the thin glass filaments (V. kilaue). In the strombolianskom type of eruptions, which creates usually stratovolcanos, together with the sufficiently abundant effusions of the liquid lavas of the basaltic and andesite- basaltic composition (are formed sometimes very long flows), which predominate appear the small explosions, which eject sculls and diverse beaten and spindle-shaped bombs (V. stromboli on Liparskikh about- VAKh, Mihara, the some eruptions Of klyuchevskoy knoll). For the domelike type is characteristic the squeezing and the ejection of viscous (andesite, dacitic or rhyolitic) lava by the strong pressure of gases from the channel v. the formation of cupolas (By v. phi-de-D and central Semyachik in Kamchatka), kriptokupolov (v. Showa -Sindzan), konusokupolov (V. Ivanov) and obelisks (V. shiveluch in Kamchatka). In the vulkanskom type large role play the gaseous substances, which generate explosions and ejections of the enormous black clouds, overfilled by a large quantity of fragments of lavas. Lavas viscous of andesite, dacitic or rhyolitic composition form the small flows (V. vul'kano, Avachinskaya knoll and Karymskaya knoll in Kamchatka). Each of the main types of eruptions is divided into several subtypes. From them separately are separated peleyskiy and katmayskiy, intermediate between the domelike and vulkanskim types. The characteristic property of the first is the formation of cupolas and the directed explosions of the very hot gas clouds, overfilled by samovzryvayushchimisya in flight and with the rolling along the slope of volcanoes fragments and chunks of the lavas (V. montan'-Pele on fan martinique). The eruptions of katmayskogo subtype are characterized by the ejection of very hot, very mobile sandy flow (To v. katmay in Alaska). The kupoloobrazuyushchiye eruptions are sometimes accompanied by the incandescent or sufficiently cooled avalanches, and also by mud flows. Ul'travulkanskiy subtype is evinced by the very strong explosions, which eject enormous quantities of fragments of lavas and species of the walls of channel. The eruptions of the underwater volcanoes, located in very deep places, are usually imperceptible, since the large pressure of water prevents explosive eruptions. In the small places the eruptions are expressed by the explosions (ejections) of enormous quantities the pair also of the gases, overfilled by the small fragments of lava. Explosive eruptions continue until the izvergayemyy material is formed the island, which is risen above sea level. After which the explosions are changed or alternate with the effusions of lava.

MAP OF THE CONTEMPORARY VOLCANISM

The products of eruption v. are gaseous (see volcanic gases), liquid (see lava) and tverdymi(sm. Volcanic rocks). Depending on the nature of eruptions and composition of magma on the surface the construction of various forms and height is formed. They are vulkanich. the apparatuses, which consist of the tube-shaped or interstitial channel, the muzzle (quite upper part of the channel), of the surrounding channel from the different sides of the powerful accumulations of lavas and volcano- fragmental products and crater (cup-shaped cavity, situated on the apex of construction). The most common forms of construction are cone-shaped (with the predominance of the ejections of fragmental material), dome-like (with the squeezing of viscous lava) and gently sloping thyroid (with the predominance of the effusions of liquid lava). Eruptions occur not only through the apical main crater, but also through the side-line (parasitic) craters, located on the slopes and on the some removal from them. With the single eruptions of the gases, which open channel to the earth's surface, the funnel-shaped cavities, bordered by annular shaft from the chunks of different species, frequently are formed; such funnels, frequently filled with water, NAZ. by maars. Strong eruptions are sometimes accompanied by cavings of the part of vulkanich. of construction, and the frequently and adjacent locality; generatrix of cavity by a diameter of from several km to first ten km NAZ. by calderas.

Geographical location of the active volcanoes (according to the data to 1970)

Numbers after sign + designate the volcanoes, whose the activity in the historical time find open to question.

Geographical Location Of those acting V. sovr. V. are located along the young mountain ranges or along the large breakings (grabens) on elongation of hundreds and thousands of km in the tectonic mobile regions (see table). Almost the bottom third v. they are concentrated on the islands and the coasts quiet ok. (Pacific Ocean vulkanich. belt). From others.

regions on the basis of a quantity acting v. is separated the region of Atlantic Ocean.

The reasons for activity V. geogr. arrangement v. indicates the close connection between the belts of vulkanich. of activity and the stationed mobile zones of the earth's crust. The breakings, which are formed in these zones, are channels, on which occurs the motion of magma to the earth's surface. The motion of magma along the cracks and the tube-shaped channels to the earth's surface, apparently, occurs under the effect of tektonich. of processes. At the depth, when the pressure of gases dissolved in the magma becomes more than the pressure of the superincumbent thicknesses, gases begin to swiftly move and to carry along magma to the earth's surface. It is possible that the gas pressure is created during the process of crystallizing the magma, when its liquid part is enriched in residual gases and vapor. Magma seemingly boils up also as a result of the intensive isolation of gaseous substances in the center is created the high pressure, which also can be one of the reasons for eruption.

Lit.: R and t m and n a., volcanoes and their activity, translated from the German, M., 1964; Taziyev g., volcanoes, trans. French, M., 1963; In even 1 1 and g d F M., Volcanoes: in history, in theory, in eruption, [ Austin ], 1962; Catalogue of the active volcanoes of the World including solfatara fields, pt 1 -, Napoli, 1951 -.

V. i. vlodavets.