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 in Ōsaki,

Miyagi Prefecture is a prefecture of Japan located in the Tōhoku region of Honshu. Miyagi Prefecture has a population of 2,305,596 (1 June 2019) and has a geographic area of . Miyagi Prefecture borders Iwate Prefecture to the north, Akita Prefecture to the nort ...

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

. The volcano consists of a 7 km wide

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 ...

with several

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 ...

s. The summit of the 470 m high Mt. Kurumigatake is one of the four lava domes located in the center of the caldera. The volcano is well known because of its relationship to the Naruko Hot Springs Villages. However, its lack of well-defined features makes it difficult to recognize for a casual observer. The Japan Metrological Agency considers Naruko to be an active volcano. The Naruko volcano was formed through two

pyroclastic flows A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at average speeds of b ...

, which occurred 73,000 and 45,000 years ago. The first lava domes were formed approximately 20,000 years ago. The rocks produced by the

and lava domes vary in composition, but are generally

dacitic 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 ...

. Subsequent volcanic activity continued to create more lava domes, while also resulting in explosive eruptions that destroyed such domes.

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 ...

created by an explosive eruption approximately 18,000 years ago is said to be related to the formation of Katanuma lake. The lake is located in the center of the volcano, and is known as one of the most acidic lakes in Japan, with a pH around 1.6. The only known historical eruption of the volcano is recorded in the ''

Shoku Nihon Kōki is an officially commissioned Japanese history text. Completed in 869, it is the fourth volume in the Six National Histories. It covers the years 833–850. Background Following the earlier national history ''Nihon Kōki'' (840), in 855 Emperor ...

''. According to the document, "In 837, the Naruko volcano suddenly began to tremble for several days and finally exploded, spouting hot water which ran like a river. The people were surprised and reported this event to the imperial court, which enshrined a

hot spring A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by circ ...

god." This event is believed to be a relatively small

phreatic eruption A phreatic eruption, also called a phreatic explosion, ultravulcanian eruption or steam-blast eruption, occurs when magma heats ground water or surface water. The extreme temperature of the magma (anywhere from ) causes near-instantaneous evapo ...

that resulted in the collapse of a lava dome. This also led to the present-day name of the volcano, which is said to be derived from "narugō" (鳴郷) or "naru koe no sato" (鳴る声の郷), which literally means "the place with a trembling sound."

References

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External links

Naruko
- Japan Meteorological Agency * - Japan Meteorological Agency

- Geological Survey of Japan * Volcanoes of Honshū Calderas of Honshū Subduction volcanoes Active volcanoes Volcanic crater lakes Volcanoes of Miyagi Prefecture Pleistocene calderas Holocene calderas {{miyagi-geo-stub

See also

References

External links