Aluchin is a

volcano 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. On Earth, volcanoes are most often found where tectonic plates are ...

along the Aluchin River in the

Chukotka Autonomous Okrug Chukotka (russian: Чуко́тка), officially the Chukotka Autonomous Okrug,, ''Čukotkakèn avtonomnykèn okrug'', is the easternmost federal subjects of Russia, federal subject of Russia. It is an autonomous okrug situated in the Russian ...

Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...

. The volcano was discovered in 1956–1957 by G.K. Kleshchev.

Description

The volcano is formed by three

cones A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex. A cone is formed by a set of line segments, half-lines, or lines conn ...

, named Alpha, Beta and Gamma, which occur along a fissure. Alpha, the main cone, formed within a river valley. It is high and has a diameter of . A crater wide and deep caps the cone. Beta, a smaller cone formed by

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...

and

scoria Scoria is a pyroclastic, highly vesicular, dark-colored volcanic rock that was ejected from a volcano as a molten blob and cooled in the air to form discrete grains or clasts.Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds. (2005) ''G ...

, grew on the southeastern side of Alpha. It ejected

lava bomb A volcanic bomb or lava bomb is a mass of partially molten rock (tephra) larger than 64 mm (2.5 inches) in diameter, formed when a volcano ejects viscous fragments of lava during an eruption. Because volcanic bombs cool after they l ...

s with sizes of up to that landed in the surrounding valleys. Beta is partially degraded, high and has a wide crater. Gamma is formed by

agglomerate Agglomerate (from the Latin ''agglomerare'' meaning "to form into a ball") is a coarse accumulation of large blocks of volcanic material that contains at least 75% bombs. Volcanic bombs differ from volcanic blocks in that their shape records flui ...

s. Because the poorly indurated agglomerates are subject to rapid erosion the cone's structure has been heavily degraded. It is high with no recognizable crater and a base size of . Volcanic activity has generated lava flows that fill a valley. These flows cover a surface area of and reach a length of . The total volume reached by the flows is , or more. Part of the lava flowed down into the valley of the Aluchin River, reaching a length of upvalley. These lava flows may be dependent on fissure eruptions along the fault rather than the cones. The eruption of the lava disrupted the river courses of the Aluchin and Burgakhchan rivers. Later the Aluchin River cut a deep gorge in the lava flow, exposing

columnar basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of a ...

s. The eruptions of the Beta and Gamma lava flows apparently occurred in three distinct events. Volcanic rocks erupted by the Aluchin volcanic cones include basalts with glass-,

pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular vol ...

- and

-like consistency.

Granodiorite Granodiorite () is a coarse-grained (phaneritic) intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar. The term banatite is sometimes used informally for various rocks ranging from gra ...

blocks are found as

xenolith A xenolith ("foreign rock") is a rock fragment (country rock) that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term ''xenolith'' is almost exclusively used to describe inclusions in igne ...

s. The lava flows contain

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...

ilmenite Ilmenite is a titanium-iron oxide mineral with the idealized formula . It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printing ...

and

magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With the ...

. The rocks of the volcano are of

trachybasalt Trachybasalt is a volcanic rock with a composition between trachyte and basalt. It resembles basalt but has a high content of alkali metal oxides. Minerals in trachybasalt include alkali feldspar, calcic plagioclase, olivine, clinopyroxene and li ...

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

composition, being a typical continental Asia alkaline series. Their formation was influenced by

pyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe II) ...

fractionation Fractionation is a separation process in which a certain quantity of a mixture (of gases, solids, liquids, enzymes, or isotopes, or a suspension) is divided during a phase transition, into a number of smaller quantities (fractions) in which the ...

. The volcano is located in part of the Anyuy area where a fault dating back possibly to the

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

cuts the terrain. Paleozoic and possibly

Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...

rocks crop out at the sides of the fault. A number of volcanic rocks, both effusive and intrusive ones, are associated with the fault and go as far back as the

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

. The lava flows of the Beta and Gamma cones apparently formed first. An age of 1000 CE was estimated for the volcanoes, on the basis of the timespan estimated for the development of soil on the lava flows and the growth of trees on them. This would make Aluchin one of the few continental Asian volcanoes with activity during the

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...

. Argon-argon dating however has yielded a much older age of 277,300 ± 2,100 years ago; that age may reflect a more general volcanic event in northeastern Russia, as other local volcanoes were also active at that time. The formation of the Alpha cone was characterized by an alternation of explosive and effusive activity. The Anyuy volcano lies farther north. It and Aluchin form the Anyuy group of volcanoes which have erupted volcanic rocks with similar composition; their activity is associated with former and present-day

plate boundaries Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...

in northeastern Russia.

References

Sources

* * * {{refend Volcanoes of Russia Mountains of Chukotka Autonomous Okrug Holocene volcanoes Holocene Asia Geology of the Russian Far East

Description

See also

References

Sources