Quaternary Volcanoes > Active Volcanoes > Nasu

Eruptions of 1408 - 1410 / Eruptions of recent times

Eruptions of 1408 - 1410
   The latest unit of magmatic eruption of Chausudake is, as mentioned before, occurred in 1408-1410, which was described in a historical notes called Shinmeikagami in early Muromachi Period ( roughly from 1333 to 1573 ). According to the record, there was an eruption in NVG on February 24th 1408 ( January 18th of the 15th year of Ouei ) and sulfur fell from the sky and discolored water of Nakagawa River yellow for several years. On March 5th 1410 ( January 21st of the 17th year of Ouei ) the NVG erpted again with thunder-like sound causing 180 strong deaths and many casualties of cattle and horses from fallen stones and burial ( Imperial Earthquake Investigation Committee, 1918 ). On the other hand, in ' Honchou Nendaiki ' and ' Zokushi Gumyou ' written during Edo Period, a brief mention of eruptions of Nasu Volcano on January 11th of the 11th year of Ouei ( 1404 in Gregorian calendar ) and January 21st of the 17th year of Ouei, but those are clearly second hand information and the years seem to be in error. Matsuda ( 1901 ) mentioned in Imperial Earthquake Investigation Committee Report No.36 that on January 11th of the 4th year of Ouei ( 1397 ditto ) and the 17th year of Ouei, Chausudake erupted. However, as the dates are the same with different years, it seems this was also an error in transcribing the dates. Therefore, we believe there were no eruptions in 1397 and 1404.

   It seems that the record of 1408 corresponds to phreatic eruption preceding magmatic eruption. Ejecta related to pyroclastic fall from phreatic eruption contained a large quantity of white to yellow colored ash altered by hydrothermal actions. These are recognizable in the eastern foot 5 km away. Rock-equivalent volume of pyroclastic fall deposits is 7.5 x 10-3 km³. From Minenochaya to uppermost stream area of Myobanzawa north of Chausudake are distributed debris flow deposits rich in altered ash. These may have entered into Nakagawa River through Yozasagawa Creek. In the old documents, there's no record describing the state of the volcano for two years after this eruption. However, in deposits of phreatic eruption of 1408-1410, clear stratification is visible, and the number of stratification increases towards the summit. This indicates that the beds were not formed by a single eruption. Probably the phreatic eruption continued with changing intensities until the eruption of 1410.

   The record of 1410 eruption suggests that some debris flow disaster occurred and this may correspond to an eruption of large quantity of pyroclastic materials with Vulcanian eruption the rock-equivalent volume of which is estimated to be 3.6 x 10-2 km³. However, the axis of distribution of fall deposits lies from Chausudake to the west and the pyroclastic flow went to the west. It seems unlikely that a village with over 180 population existed at that time to the west of the volcano. ( Santogoyashuku village was established when a new road, Matsukawa-Shindo, was opened after the Nikko earthquake in 1682 ). Details are hard to identify where the disaster actually struck, but a possibility of debris avalanche can be imagined ( Mitsuru Okuno and Nasu Volcano Research Group, 1996 ). In this scenario, pyroclastic deposits once filled upstream area of Nakagawa River was remobilized by rain or melt snow and flowed down the Nakagawa River for about 10 km, the villages along the southern foot of the volcano might have been hit by debris avalanche. In the eruption of 1410, lava flow with rock-equivalent volume of 6.2 x 10-3 km³ erupted following the Vulcanian eruption, but this was not recorded in the documents.

Eruptions of recent times
   After 1410, there's no record of eruption until 1846 ( 3rd year of Koka ) and the volcano kept quiescence for about 400 years. It is not clear which part of Chausudake the 1846 eruption occurred, but after this, Chausudake resumed active fumarolic action. Deposits corresponding to this eruption are nowhere to be found. Therefore, it must be a micro phreatic eruption with rock-equivalent volume of less than 10-4km³.

   Small eruption which left deposits occurred on July 1st 1881 ( 14th year of Meiji ) ( Fig.4 ). It was a phreatic eruption and the ejecta consisted of hydrothermally altered lapilli and yellow ash. There was no casualty, but many fishes were killed in Nakagawa River to which altered ash flowed into. Rock-equivalent volume of fall deposits is 1.5 x 10-3 km³ and the thickness measured at 2 km away at Nasudake skiing ground is 5 cm. According to a record, the fall was carried to the east by strong wind and ash fall was observed in the city of Shirakawa about 20 km away. Mugen crater to the west of Chausudake summit and another crater at NW side were both formed by this eruption.

   Chronology of Chausudake eruptions after 1881 is as follows. The fumaroles and craters are restricted within the craters of 1881 eruption. The deposits related to any of the eruptions are not recognized even close to the crater. Therefore, these were estimated to be micro phreatic eruptions. Active fumarolic action in 1881 crater continues to this day.

   October-December 1942 ( 17th year of Showa ) Fumarolic action in the west of Chausudake intensified.

   December 1943 ( 18th year of Showa ) Fumarolic action in the west of Chausudake intensified and black smoke rose.

   October 24th and 29th 1953 ( 28th year of Showa ) Micro eruption with small crater created in fumarole area west of Chausudake. Ash fall reached 6 km to the south.

   On or around October 10th 1960 ( 35th year of Showa ) micro eruption occurred with creation of small crater with diameter of 2-3 m within the fumarole area west of Chausudake. Head sized blocks were ejected around crater and small amount of ash fell 0.8 km north from crater.

   July 10th to 11th 1963 ( 38th year of Showa ) Unusual sound was heard. Micro eruption occurred in fumarole area west of Chausudake with little ash fall.

   January 30th to 31st 1977 ( 52nd year of Showa ) Seismic swarm felt.

   September 9th to 12th, 27th to 29th, and December 16th 1985 ( 60th year of Showa ) Seismic swarm felt in northern foot area.

   March 12th 1986 ( 62nd year of Showa ) Seismic swarm several km north of Chausudake summit. July 1st to 4th of the same year, seismic swarm felt in SE foot area.

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