Nemo Peak

Nemo Peak (Template:Langx; Japanese 根茂山; Nemoyama) is a stratovolcano located at the northern end of Onekotan Island, Kuril Islands, Russia. It is truncated by two nested calderas, with the cone of Nemo Peak itself rising in the southwest end of the youngest caldera and a crater lake partially filling the northeast part, named Ozero Chernoye.

Geography

File:Onekotan Island, Kuril Islands, Russian Federation.JPG

Astronaut photograph of Onekotan from the International Space Station, with Nemo Peak at right (north)

Nemo Peak lies on Onekotan Island, in the Kuril Islands.Template:Sfn Nemo Peak lies on the northern end of the island; the southern end is occupied by Tao-Rusyr Caldera.Template:Sfn These two volcanoes together have erupted about of tephra, covering the entire seafloor of the Sea of Okhotsk.Template:Sfn

Geology

Nemo Peak has formed several calderas. Two older ones reach diameters of and overlap each other,Template:Sfn with an average elevation of the floor of . The Sovetskii ridge limits these calderas to the east.Template:Sfn A pre-Nemo volcano is known as Mednyi.Template:Sfn Glacial erosion has affected the older volcanic centres.Template:Sfn Ignimbrites fill these calderas.Template:Sfn

Within this caldera lies a stratovolcano with a smaller wide caldera; Nemo Peak proper is located within this smaller caldera.Template:Sfn This forms a somma volcano.Template:Sfn In the north-northeastern part of this caldera, Black Lake can be found, also known as Chernoe.Template:Sfn The caldera opens towards the Sea of Okhotsk.Template:Sfn

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.Template:Sfn Lava flows extend down from the summit area of Nemo PeakTemplate:Sfn and are covered with scoria.Template:Sfn

The complex is surrounded by older rocks, some of Tertiary age.Template:Sfn To the south the complex borders the old Tao-Rusyr and Shestakov volcanic rocks.Template:Sfn Another volcano named Asyrmintar is found on the northeastern margin of the two older calderas;Template:Sfn Asyrmintar is an eroded remnant.Template:Sfn

Petrology

Nemo is an andesitic volcano.Template:Sfn Basaltic andesite and dacite have been found as well.Template:Sfn

Augite, hypersthene, labradorite, olivine and pyroxene are minerals found in Nemo lavas.Template:Sfn

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. Such large eruptions released large amounts of pyroclastics. Old eruptions occurred 199,000 - 200,000 years ago.Template:Sfn Detailed eruption histories however are poorly established.Template:Sfn

The older Nemo calderas appear to predate the last glaciation, while the younger one is post-glacial in age.Template:Sfn Nemo I formed 40,000 - 45,000 years ago and Nemo III 25,000 - 24,500Template:Sfn or 26,000 years ago;Template:Sfn a radiocarbon date of 24,500 ± 740 years ago has been obtained on it.Template:Sfn Nemo Peak proper formed about 9,050 ± 100 or 9,130 ± 140 radiocarbon years ago.Template:Sfn

Holocene volcanic activity includes the emission of tephra and lava flows with eruptions every 1,400 - 1,200 years since 3,800 years before present. The growth of a lava dome over the last 600 years was accompanied by phreatic activity.Template:Sfn Tephrochronology 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.Template:Sfn It was the site of volcanic unrest in the 1700s, 1938 and 1906. This last eruption may be associated with the formation of a lava dome.Template:Sfn The summit area features solfataric activity,Template:Sfn which occurs on a bench in the summit lava dome.Template:Sfn Future volcanic activity involving medium-sized or large eruptions is possible; tephra would be propagated east-northeast.Template:Sfn

Tephras

Nemo Peak appears to be the source of several tephra layers found in the Sea of Okhotsk named K2 and K3. These tephras extend up to away from Onekotan IslandTemplate:Sfn but their locations do not overlap:Template:Sfn K2 tephras extend northwestward away from OnekotanTemplate:Sfn and pyroxenes crystallized under different conditions.Template:Sfn The volume of the K2 tephra has been estimated at .Template:Sfn This tephra is of rhyolitic composition.Template:Sfn

It is not clear if they come from different phases of the same eruption or different ones,Template:Sfn 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.Template:Sfn An alternative proposal attributes K3 to the Nemo I caldera.Template:Sfn

See also

• List of volcanoes in Russia