Moekeshiwan, also known as Lvinaya Past (russian: Львиная Пасть, literally "''Lion's Maw''", after a rock that emerges from the sea and resembles a sleeping lion), is a volcano in the southern part of Iturup in the

Kuril Islands The Kuril Islands or Kurile Islands (; rus, Кури́льские острова́, r=Kuril'skiye ostrova, p=kʊˈrʲilʲskʲɪjə ɐstrɐˈva; Japanese: or ) are a volcanic archipelago currently administered as part of Sakhalin Oblast in the ...

, claimed by Japan and administered by Russia. The volcano is characterized by a large

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...

that is flooded by the Sea of Okhotsk. A large eruption occurred early 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 togeth ...

which reached a volcanic explosivity index of 7.

Location

Iturup island contains about nine stratovolcanoes, some pyroclastic cones, one

somma volcano A somma volcano (also known as a sommian) is a volcanic caldera that has been partially filled by a new central cone. The name comes from Mount Somma, a stratovolcano in southern Italy with a summit caldera in which the upper cone of Mount Ves ...

and several geothermal fields. Among these, Lvinaya Past is formed by a wide and deep caldera, which is connected with the Sea of Okhotsk by a wide and maximally deep strait. The volcano is high, almost above the bottom of the caldera. The caldera lies close to the southernmost point of Iturup and is flanked to the east by the Urbich volcano and to the southwest by the Berutarube volcano. The isthmuses east and southwest of Lvinaya Past are covered by its eruption products.

Series of eruptions

Large eruptions took place 13,000 and 12,300 years ago, and a major eruption occurred 7480 ± 80 BC. The submarine caldera formed during this eruption and heavily altered the topography on Iturup, generating an

ignimbrite Ignimbrite is a type of volcanic rock, consisting of hardened tuff. Ignimbrites form from the deposits of pyroclastic flows, which are a hot suspension of particles and gases flowing rapidly from a volcano, driven by being denser than the surro ...

which joined the three southernmost volcanoes of Iturup to the main island. The total volume of tephra ejected amounts to . This eruption had a volcanic explosivity index of 7, making it one of the largest eruptions that are known to have occurred in the Kuril Islands, and the strongest known to have occurred during the Holocene in the Southern Kurils.

Younger Dryas eruptions and their impact

Ice cores taken in the Siberian Altai demonstrate increased

sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...

concentrations at the time, possibly stemming from large sulfate release by the eruptions of Lvinaya Past and contemporaneous large scale activity at Caldera Fisher in

Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S. ...

and Pinatubo in the

Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...

and may relate to the

Younger Dryas The Younger Dryas (c. 12,900 to 11,700 years BP) was a return to glacial conditions which temporarily reversed the gradual climatic warming after the Last Glacial Maximum (LGM, c. 27,000 to 20,000 years BP). The Younger Dryas was the last stag ...

event. Habitats may have been destroyed to distances of from the volcano. The development of

alder Alders are trees comprising the genus ''Alnus'' in the birch family Betulaceae. The genus comprises about 35 species of monoecious trees and shrubs, a few reaching a large size, distributed throughout the north temperate zone with a few sp ...

-containing birch forests in the region may have been favoured by the ash fall from the eruption, which would have killed more susceptible conifers. The impact of the eruption may have extended all the way to southern North America.

Magma content

Lvinaya Past has erupted tholeiitic magmas with a low

potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosph ...

content. Other rocks include

andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predo ...

, basaltic andesite,

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 ...

dacite Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite ...

and

picrite Picrite basalt or picrobasalt is a variety of high-magnesium olivine basalt that is very rich in the mineral olivine. It is dark with yellow-green olivine phenocrysts (20-50%) and black to dark brown pyroxene, mostly augite. The olivine-rich p ...

. The caldera-forming eruption ejected dacitic material with

hornblende Hornblende is a complex inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common in igneous and metamorphic rock ...

and

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...

forming

phenocryst 300px, feldspathic phenocrysts. This granite, from the Switzerland">Swiss side of the Mont Blanc massif, has large white plagioclase phenocrysts, triclinic minerals that give trapezoid shapes when cut through). 1 euro coins, 1 euro coin (diameter ...

Nearby volcanoes

Other volcanoes on Iturup include Astonupuri, Baransky, Berutarube, Bogatyr Ridge, Chirip, Demon, Golets-Tornyi, Grozny Group, Medvezhy and Past.

References