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  • Volcanic Region
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  • Last Known Eruption
  • 39.099°N
  • 140.049°E

  • 2236 m
    7334 ft

  • 283220
  • Latitude
  • Longitude

  • Summit

  • Volcano

The Global Volcanism Program has no activity reports for Chokaisan.

The Global Volcanism Program has no Weekly Reports available for Chokaisan.

Index of Monthly Reports

Reports are organized chronologically and indexed below by Month/Year (Publication Volume:Number), and include a one-line summary. Click on the index link or scroll down to read the reports.

04/1974 (CSLP 50-74) Explosions cause ashfall in March and April

Contents of Monthly Reports

All information contained in these reports is preliminary and subject to change.

04/1974 (CSLP 50-74) Explosions cause ashfall in March and April

Card 1835 (01 April 1974) Large ash eruptions on 1 March from the E side of the central cone

After a long period of inactivity (since 1821), Tyokai volcano blew up on 1 March. Explosions at 1010 and 1130 (0110 and 0230 GMT) were the biggest, and repeated about ten times. Black smoke rose, and the volcanic ash fall lasted for ten minutes. According to aerial observations that same day, the eruption site was confirmed to be located on the eastern side of Sinzan, a central cone of this volcano. At first black smoke was spewing from the crater, and black ash was deposited on the eastern slope of the snow-covered volcano. According to an aerial observation on 3 March, this black smoke had turned into white vapor. Temporary seismic observations were carried out by the Tohoku University and the JMA around the skirt of this volcano, and scores of volcanic earthquakes were detected. A black belt (about 1.5 km long and 20-30 m wide) composed of ash-deposits and snow flowed down to the north side on 6 March. This belt is considered to be the result of a snow slide and there was no change or re-activity in the volcanic state. Gray volcanic smoke was observed on 5 March from the slope of the volcano, but there was no smoke after that.

Card 1850 (30 April 1974) Intermittent variable actiivty; ashfall on 24 April

The activity of Tyokai volcano started with the black smoke eruption and the volcanic ash fall on 1 March, but showed decreasing activity thereafter. Recently, however, the activity increased, and the following phenomena took place:

1) According to a visual observation on 8 April, and an aerial observation on 15 April, white smoke several tens of meters in height erupted from the new crater on the eastern flank of Sinzan, a central cone of this volcano, and white vapor about 20 m in height erupted from the 500 m long fissure on the western flank of Sinzan. On the fissure about ten fumaroles have formed.

2) On 24 April, black smoke, about several hundred meters in height, rose from the fissure on the W flank of Sinzan, and ash fell on the E foot of Tyokai volcano. On that day this black smoke gradually turned into white vapor. Simultaneously, a mud flow started from the summit crater and flowed down the W side, and this belt reached 3 km in length.

Information Contacts:
Card 1835 (01 April 1974) T. Tiba, Dept. of Geology, National Science Museum, Tokyu, Japan.
Card 1850 (30 April 1974) Seismological Division, JMA.

Massive Chokaisan volcano, the largest of NE Honshu, overlooks the Japan Sea. It is composed of two overlapping stratovolcanoes with a conical profile that has given it the local names Akita-Fuji or Dewa-Fuji. The summit of the gently sloping western volcano (Nishi-Chokaisan) is cut by a large horseshoe-shaped caldera breached to the south, whose floor contains lava domes. The younger eastern volcano (Higashi-Chokaisan) began forming about 20,000 years ago. It was cut by another large horseshoe-shaped caldera, breached to the north. During an eruption about 2600 years ago it was the source of the voluminous Kisakata debris avalanche, which reached the Pacific coast. Two post-caldera lava domes have been constructed at the upper SE end of the caldera. Intermittent reports of historical eruptions date back to the 6th century CE.

Summary of Holocene eruption dates and Volcanic Explosivity Indices (VEI).

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
1974 Mar 1 1974 Apr 30 Confirmed 1 Historical Observations E side of Shinzan, W of Kojin-yama
1834 Jul 9 1834 Jul Confirmed 2 Historical Observations
1821 May 23 Unknown Confirmed 2 Historical Observations Near Shinzan and Shichiko-zan
1800 Dec 1804 Jul (?) Confirmed 2 Historical Observations Shinzan (foot of Kojin-yama)
[ 1764 ] [ Unknown ] Uncertain 2  
1740 Jun (?) 1747 (?) Confirmed 2 Historical Observations Small crater at foot of Kojin-yama
[ 1738 Dec 31 ± 365 days ] [ Unknown ] Uncertain 2  
[ 1735 ] [ Unknown ] Uncertain 2  
1659 Apr 1663 ± 1 years Confirmed   Historical Observations
[ 1560 ] [ Unknown ] Uncertain    
[ 1477 ] [ Unknown ] Uncertain    
[ 0999 ] [ Unknown ] Uncertain    
[ 0948 Dec 31 ± 365 days ] [ Unknown ] Uncertain    
0939 May 15 Unknown Confirmed   Historical Observations
[ 0915 Aug 23 ] [ 0915 Sep 1 ] Discredited    
[ 0884 Jul 26 ] [ 0884 Aug ] Uncertain    
0871 May 5 Unknown Confirmed 2 Historical Observations
[ 0861 May ] [ Unknown ] Uncertain 3  
[ 0857 May ] [ Unknown ] Uncertain    
[ 0856 ] [ Unknown ] Uncertain    
[ 0839 Oct 14 ] [ Unknown ] Uncertain    
0830 Jan Unknown Confirmed   Historical Observations
0817 ± 7 years Unknown Confirmed   Historical Observations
[ 0804 ] [ 0806 ] Uncertain    
[ 0717 Jul ] [ Unknown ] Uncertain    
0711 ± 3 years Unknown Confirmed   Historical Observations
[ 0610 ± 18 years ] [ Unknown ] Uncertain    
[ 0577 Dec 1 ± 30 days ] [ 0578 Jul 15 ± 45 days ] Uncertain    
[ 0573 Mar (?) ] [ Unknown ] Uncertain    
0450 BCE (?) Unknown Confirmed   Tephrochronology OD-12 tephra
0650 BCE (?) Unknown Confirmed   Radiocarbon (uncorrected) Higashi-Chokai
1050 BCE (?) Unknown Confirmed 0 Tephrochronology West flank (Saruana crater)

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.

Tyokai | Tekai | Chokai-san | Dewa-Fuji | Akita-Fuji | Chokai

Feature Name Feature Type Elevation Latitude Longitude
Higashi-Chokai Stratovolcano 2230 m
Kannon-mori Cone 685 m
Nishi-Chokai Stratovolcano

Feature Name Feature Type Elevation Latitude Longitude
Saruana Crater
Tamano-ike Crater
Torinoumi Crater 1600 m

Feature Name Feature Type Elevation Latitude Longitude
Kyowa-yama Dome
Nabemori Dome
Sensumori Dome
Dome 2233 m 39° 5' 47" N 140° 3' 8" E
Massive Chokai volcano, the largest of NE Honshu, is seen here from the NE. Chokai is composed of two large overlapping stratovolcanoes. The younger eastern volcano is cut by the large horseshoe-shaped caldera, seen here breached to the north, that was the source of the Kisakata debris avalanche. Pyroclastic cones later filled much of the area near the back wall of the caldera. Chokai has erupted frequently since one of the earliest historically documented eruptions in Japan in 573 AD.

Photo courtesy Ichio Moriya (Kanazawa University).
The north flank of Chokai volcano was the source of a massive debris avalanche about 2600 years ago that traveled 25 km into the Japan Sea and underlies much of the foreground area. Collapse of the summit left a 3 x 4 km horseshoe-shaped caldera whose eastern rim forms the peak at left center and western rim descends from the cloud bank at the right. Following the collapse a series of lava domes and lava flows filled the upper part of the caldera and formed the center peak.

Photo by Ichio Moriya (Kanazawa University).
An ash plume rises from the flanks of Shinzan lava dome at the summit of Chokai volcano on March 1, 1974, after a long repose of 140 years. Phreatic eruptions occurred at Chokai in March and April, and were accompanied by small mudflows. The eruptions took place from an E-W-trending series of vents extending from the eastern caldera wall across the flanks of the 1801 Shinzan lava dome and the Kojin-yama cone. This view from the NW shows the eastern caldera wall behind Shinzan.

Photo courtesy of Japan Meteorological Agency, 1974.
Steam pours from an eruptive fissure on Chokai volcano on April 24, 1974, near the end of an eruption that began on March 1. Ash darkens the slopes of the summit cone and mudflow deposits descend the flanks at the lower left. Shinzan lava dome appears above the steam plume at the left, with the eastern caldera wall in the background, in this view from the SW. The 1974 eruption, the first from Chokai in 140 years, ended on April 30.

Photo courtesy of Japan Meteorological Agency, 1974.

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.

Ban M, Hayashi S, Takaoka N, 2001. K-Ar dating of the Chokai volcano, northeast Japan arc--a compound volcano composed of continuously established three stratovolcanoes. Bull Volc Soc Japan (Kazan), 46: 317-333 (in Japanese with English abs).

Hasenaka T, Ui T, Nakamura Y, Hayashi S, 1992. Traverse of Quaternary volcanoes in Japan. 29th Internatl Geol Cong, Kyoto, Field Trip A06, 74 p.

Japan Meteorological Agency, 1996. National Catalogue of the Active Volcanoes in Japan (second edition). Tokyo: Japan Meteorological Agency, 502 p (in Japanese).

Japan Meteorological Agency, 2013. National Catalogue of the Active Volcanoes in Japan (fourth edition, English version). Japan Meteorological Agency.

Kudo T, Hoshizumi H, 2006-. Catalog of eruptive events within the last 10,000 years in Japan, database of Japanese active volcanoes. Geol Surv Japan, AIST,

Kuno H, 1962. Japan, Taiwan and Marianas. Catalog of Active Volcanoes of the World and Solfatara Fields, Rome: IAVCEI, 11: 1-332.

Murayama I, 1987. Volcanoes of Japan (I). Tokyo: Daimedo, 315 p (2nd edition, in Japanese).

Nakano S, Yamamoto T, Iwaya T, Itoh J, Takada A, 2001-. Quaternary Volcanoes of Japan. Geol Surv Japan, AIST,

Volcano Types

Lava dome(s)

Tectonic Setting

Subduction zone
Continental crust (> 25 km)

Rock Types

Andesite / Basaltic Andesite
Basalt / Picro-Basalt


Within 5 km
Within 10 km
Within 30 km
Within 100 km

Affiliated Databases

Large Eruptions of Chokaisan Information about large Quaternary eruptions (VEI >= 4) is cataloged in the Large Magnitude Explosive Volcanic Eruptions (LaMEVE) database of the Volcano Global Risk Identification and Analysis Project (VOGRIPA).
WOVOdat WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.
EarthChem EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).
Smithsonian Collections Search the Smithsonian's NMNH Department of Mineral Sciences collections database. Go to the "Search Rocks and Ores" tab and use the Volcano Name drop-down to find samples.