Nemo Peak (russian: Пик Немо) is a

stratovolcano A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and per ...

located at the northern end of

Onekotan Onekotan (russian: Онекотан; Japanese 温禰古丹島; Onekotan-tō, occasionally Onnekotan-tō, ain, オネコタン　or　オネコタㇴ) is an uninhabited volcanic island located near the northern end of the Kuril Islands chain in t ...

Island,

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 ...

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 ...

. It is truncated by two nested

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 ...

s, with the cone of Nemo Peak itself rising in the southwest end of the youngest caldera and a

crater lake Crater Lake (Klamath language, Klamath: ''Giiwas'') is a volcanic crater lake in south-central Oregon in the western United States. It is the main feature of Crater Lake National Park and is famous for its deep blue color and water clarity. The ...

partially filling the northeast part, named Ozero Chernoye.

Geography

Nemo Peak lies on Onekotan Island, in the Kuril Islands. Nemo Peak lies on the northern end of the island; the southern end is occupied by

Tao-Rusyr Caldera Tao-Rusyr Caldera (russian: Тао-Русыр) is a stratovolcano located at the southern end of Onekotan Island, Kuril Islands, Russia. It has 7.5 km wide caldera formed during a catastrophic eruption less than 10,000 years ago (reported a ...

. These two volcanoes together have erupted about of tephra, covering the entire seafloor of the Sea of Okhotsk.

Geology

Nemo Peak has formed several calderas. Two older ones reach diameters of and overlap each other, with an average elevation of the floor of . The Sovetskii ridge limits these calderas to the east. A pre-Nemo volcano is known as Mednyi.

Glacial A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...

erosion has affected the older volcanic centres.

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 surrou ...

s fill these calderas. Within this caldera lies a

with a smaller wide caldera; Nemo Peak proper is located within this smaller caldera. This forms a

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

. In the north-northeastern part of this caldera, Black Lake can be found, also known as Chernoe. The caldera opens towards the Sea of Okhotsk. Evidence indicates that Nemo Peak proper contains a southwestern crater filled with the present-day cone and crater, which is in turn filled by a lava dome. A smaller cone on the northwestern side of Nemo Peak was destroyed by an explosion.

Lava flow 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 und ...

s extend down from the summit area of Nemo Peak and are covered with

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 ...

. The complex is surrounded by older rocks, some of

Tertiary Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...

age. To the south the complex borders the old Tao-Rusyr and Shestakov volcanic rocks. Another volcano named Asyrmintar is found on the northeastern margin of the two older calderas; Asyrmintar is an eroded remnant.

Petrology

Nemo is an

andesitic 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 predomina ...

volcano.

Basaltic andesite Basaltic andesite is a volcanic rock that is intermediate in composition between basalt and andesite. It is composed predominantly of augite and plagioclase. Basaltic andesite can be found in volcanoes around the world, including in Central Ameri ...

and

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. ...

have been found as well.

Augite Augite is a common rock-forming pyroxene mineral with formula . The crystals are monoclinic and prismatic. Augite has two prominent cleavages, meeting at angles near 90 degrees. Characteristics Augite is a solid solution in the pyroxene group. ...

hypersthene Hypersthene is a common rock-forming inosilicate mineral belonging to the group of orthorhombic pyroxenes. Its chemical formula is . It is found in igneous and some metamorphic rocks as well as in stony and iron meteorites. Many references have f ...

labradorite Labradorite (( Ca, Na)( Al, Si)4 O8) is a calcium-enriched feldspar mineral first identified in Labrador, Canada, which can display an iridescent effect ( schiller). Labradorite is an intermediate to calcic member of the plagioclase series. It ...

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 ...

and

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) ...

are minerals found in Nemo lavas.

Eruptive history

Nemo Peak is one of the most active volcanoes in the Kurils and has been the site of catastrophic eruptions for 300,000 years, going back to the

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

. Such large eruptions released large amounts of

pyroclastic Pyroclastic rocks (derived from the el, πῦρ, links=no, meaning fire; and , meaning broken) are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroc ...

s. Old eruptions occurred 199,000 - 200,000 years ago. Detailed eruption histories however are poorly established. The older Nemo calderas appear to predate the last glaciation, while the younger one is post-glacial in age. Nemo I formed 40,000 - 45,000 years ago and Nemo III 25,000 - 24,500 or 26,000 years ago; a

radiocarbon Carbon-14, C-14, or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and coll ...

date of 24,500 ± 740 years ago has been obtained on it. Nemo Peak proper formed about 9,050 ± 100 or 9,130 ± 140

years ago.

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 ...

volcanic activity includes the emission of

tephra Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size, or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, they rem ...

and

lava flow 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 und ...

s with eruptions every 1,400 - 1,200 years since 3,800 years before present. The growth of a

lava dome In volcanology, a lava dome is a circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Dome-building eruptions are common, particularly in convergent plate boundary settings. Around 6% of eruptions on ...

over the last 600 years was accompanied by

phreatic ''Phreatic'' is a term used in hydrology to refer to aquifers, in speleology to refer to cave passages, and in volcanology to refer to a type of volcanic eruption. Hydrology The term phreatic (the word originates from the Greek , meaning "well" ...

activity.

Tephrochronology 250px, Tephra horizons in south-central Iceland. The thick and light coloured layer at the height of the volcanologist's hands is rhyolitic tephra from Hekla. Tephrochronology is a Geochronology, geochronological technique that uses discrete la ...

suggests the occurrence of eruptions 1,350, 750 AD, 550 ± 100 BC, 1,850 BC, 3,050 BC, 5,550 BC, 7,050 BC and 7,550 BC. Nemo Peak is a

dormant 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 a ...

. It was the site of volcanic unrest in the 1700s, 1938 and 1906. This last eruption may be associated with the formation of a

. The summit area features

solfataric A fumarole (or fumerole) is a vent in the surface of the Earth or other rocky planet from which hot volcanic gases and vapors are emitted, without any accompanying liquids or solids. Fumaroles are characteristic of the late stages of volcani ...

activity, which occurs on a bench in the summit lava dome. Future volcanic activity involving medium-sized or large eruptions is possible; tephra would be propagated east-northeast.

Tephras

Nemo Peak appears to be the source of several

layers found in the

Sea of Okhotsk The Sea of Okhotsk ( rus, Охо́тское мо́ре, Ohótskoye móre ; ja, オホーツク海, Ohōtsuku-kai) is a marginal sea of the western Pacific Ocean. It is located between Russia's Kamchatka Peninsula on the east, the Kuril Islands ...

named K2 and K3. These tephras extend up to away from Onekotan Island but their locations do not overlap: K2 tephras extend northwestward away from Onekotan and

s crystallized under different conditions. The volume of the K2 tephra has been estimated at around . This tephra is of

rhyolitic Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...

composition. It is not clear if they come from different phases of the same eruption or different ones, but they certainly are different tephras given their different distribution. Potentially, K3 was formed by the caldera-forming eruption of Nemo II and K2 by eruptions of Nemo III. An alternative proposal attributes K3 to the Nemo I caldera.

References

Sources

* * * * * * * * {{Kuril Islands Onekotan Stratovolcanoes of Russia Volcanic crater lakes Calderas of Russia Volcanoes of the Kuril Islands Mountains of the Kuril Islands Pleistocene calderas