Zao Volcano

Updated: Apr 22, 2025 05:45 GMT - refresh

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Honshu (Japan), 38.14°N / 140.44°E

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Summit height: 1841 m / 6,040 ft

Current status: normal or dormant (1 out of 5)

Last update: 21 Dec 2021 (Smithsonian / USGS Weekly Volcanic Activity Report)

Zao (or Zaozan, Zaosan) volcano is the most active volcano of northern Honshu and consists of a group of stratovolcanoes forming the crest of the divide between the Pacific Ocean and the Japan Sea.
The older parts of the complex are Ryuzan volcano in the west and Byobu and Fubo volcanoes forming the southern group. Zao volcano proper (Chuo-Zao) is the youngest edifice and forms the central part of the group. One of its youngest summit lava domes is Goshiki-dake, which contains the active Okama crater, the source of most of the frequent historical eruptions recorded since the 8th century AD.
Okama crater contains a colorful, strongly acidic crater lake (pH 1.3).

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News/Updates | Earthquakes | Images

Typical eruption style: explosive (phreatic)
Zao volcano eruptions: 1940, 1939 (?), 1927 (?), 1905, 1897 (?), 1896, 1895, 1895, 1894, 1890 (?), 1873, 1867, 1833, 1831, 1830, 1822, 1821, 1809, 1806, 1804, 1796, 1794, 1694, 1670, 1669, 1668, 1641, 1630, 1623-24, 1622, 1620, 1400 ± 100 years (radiocarbon), 1350 (?), 1331-33 (?), 1230, 1227, 1183, 884, 773 (?), 300 AD ± 200 (RC), 1600 BC (?, RC), 2000 BC ± 500 (tephrochronology), 2300 BC ± 75 (RC), 2600 BC ± 200 (RC), 3350 BC ± 50 (RC), 3850 BC ± 200 (RC), 4150 BC ± 200 (RC), 5500 BC (?, RC), 5600 BC (?, RC), 7600 BC (?, RC)

Latest nearby earthquakes

Date and Time	Mag / Depth	Distance / Location
Apr 17, 03:05 pm (GMT +9)	0.9 5.8 km	30 km (19 mi) to the N	Japan: Southern Yamagata Pref	Info
Apr 17, 09:37 am (GMT +9)	0.9 3.4 km	9.9 km (6.2 mi) to the W	Japan: Southern Yamagata Pref	Info
Thursday, April 10, 2025 GMT (1 quake)
Apr 10, 09:58 am (GMT +9)	1.0 3.4 km	9.6 km (6 mi) to the W	Japan: Southern Yamagata Pref	Info

View recent quakes

Background

The Pleistocene Ryuzan volcano forms the western Zao group (Nishi-Zao), and Byobu and Fubo volcanoes form the southern Zao group (Minami-Zao). The complex was constructed over granitic basement rocks as high as 1500 m and thus has a relatively small volume. The 7 cu km Zao volcano proper forms the central ao group (Chuo-Zao), a volcanic complex topped by several lava domes and the Goshiki-dake tuff cone, aligned along a NW-SE trend. Several episodes of edifice collapse produced debris avalanches during the Pleistocene.

Zao Volcano Photos

The green Okama crater lake of Zao volcano, NE Honshu, Japan (Photo: Tom Pfeiffer)

Okama crater lake, Zao volcano, Japan (Photo: Tom Pfeiffer)

Erosion gullies at the outer slopes of the inner crater containing the Okama lake, Zao volcano, Japan (Photo: Tom Pfeiffer)

Lava flows and pyroclastic layers exposed in the crater walls of Zao volcano (Photo: Tom Pfeiffer)

More photos

Significant volcanic eruptions: Zao volcano

In the past 10,000 years, Zao has had at least 43 confirmed volcanic eruptions, out of which 31 are documented by historical records, while the others can be inferred from geological evidence.
Additionally, there are 9 uncertain or discredited eruptions from Zao volcano.

The table below lists all known eruptions (date in bold face) of Zao volcano since around 1800. Updates on the most recent volcanic activity of Zao can be found on the news page of Zao volcano.

Date	Note	VEI	Deaths
1940 May 18	Okama Historical obs./docs.	1
?? 1939 Jul	Uncertain Eruption	1?
?? 1927	Uncertain Eruption	1?
1906	Discredited Eruption
1905	Okama Historical obs./docs.	1?
?? 1897 Jan 14	Uncertain Eruption	1?
?? 1896 Sep 1 ?	Uncertain Eruption	1?
1896 Mar 8	Okama Historical obs./docs.	1
1895 Aug 22 - Sep 28	Okama Historical obs./docs.	2
1895 Feb 15 - Mar 22	Okama Historical obs./docs.	1
1894 Jul 3	Okama Historical obs./docs.	2?
?? 1890	Uncertain Eruption	1?
1873 Aug - Sep	Okama Historical obs./docs.	1?
1867 Oct 21	Okama Historical obs./docs.	2
1867 Oct 21 (eruption 1867 Oct 21)	Historical obs./docs.	2	3	Info
1867 Oct 21: Overflow of muddy water from Okama crater lake killed 3 hot springs bathers at E foot of Goshiki-dake. (reference #9675) Okama boiled. 3 people were killed by flooding. (reference #12936) Cited references #1412 Simkin, Tom, and Lee Siebert with the collaboration of Russell Blong, Jonathan Dehn, Christopher Newhall, Roland Pool, and Thomas C. Stein (1994): Volcanoes of the World, Second Edition, A Regional Directory, Gazetteer, and Chronology of Volcanism During the Last 10,000 Years, Geoscience Press, Inc., Tucson, Arizona, in association with Smithsonian Institution, Global Volcanism Program, Washington, D.C., p. 164-176. #12936 Japan Meteorological Agency and Volcanological Society of Japan (2013): National Catalogue of the Active Volcanoes in Japan (fourth edition, English version). Japan Meteorological Agency. [accessed May 20, 2021] Link Source: NOAA National Centers for Environmental Information (NCEI), Global Significant Earthquake Database. doi:10.7289/V5TD9V7K
1833	Okama Historical obs./docs.	2
1831 Nov 22	Okama Historical obs./docs.	2
1830	Okama Historical obs./docs.	2
1822 May 1	Historical obs./docs.	?
1821 Jan 27 - May 1	Okama Historical obs./docs.	2
1809 Jun 12 - Dec 29	Okama Historical obs./docs.	2
1806 Jul 12	Okama Historical obs./docs.	2
1804 May	Okama Historical obs./docs.	2

Remark:

Our list of volcanic eruptions closely follows the database of eruptions of the Smithsonian's Global Volcanism Project (GVP), the internationally most recognized data source for volcanic eruptions, but also includes significant eruptive episodes or related volcano events. "Volcanic eruptions" are usually to be understood as sequences of individual eruptive episodes that can follow each other, or even overlap (if several vents are involved), and can last many years, decades or even longer. For example, the current activity of Stromboli volcano is understood as a single eruption that has been ongoing since 1934.

Sources: NOAA National Centers for Environmental Information (NCEI), Global Significant Volcanic Eruptions Database. doi:10.7289/V5TD9V7K | Global Volcanism Project / Smithsonian Institution

Eruptions of Zao volcano

1992 earthquake
A M 4.7 earthquake occurred at 17h58 local time on 1 September a few kilometers ESE of the summit. There were no visible changes.

1990 seismic swarm
In July 1990, many small earthquakes were detected below the summit of Zao volcano.
(GVP)

1867 phreatic eruption and fatalities
On 21 Oct 1867, a phreatic eruption caused an overflow of muddy water from Okama crater lake, which killed 3 bathers who were in the hot springs at the foot of Goshiki-dake. ...more info

Zao Volcano FAQ

+When was the last eruption of Zao volcano?

The last confirmed eruption of Zao occurred in 1940.

+How often does Zao volcano erupt?

Since 884 AD, Zao volcano has had at least 31 historically documented eruptions. This means that it erupts on average every 36.8 years.

+How active is Zao volcano at present?

Zao volcano is occasionally active: Since 1900, it has had 2 eruptions, and been active during 2 years out of 126 as of now. This means, Zao has been in eruption one in 63 years on average. The last eruption was in 1940 and ended 85 years ago.

+When was the largest eruption of Zao volcano?

The largest eruption known from the younger geological history of Zao volcano occurred around 300 AD. It ranks as a "vulcanian" eruption with a magnitude 3 on the VEI (Volcanic Explosivity Index) scale.

Latest satellite images

See also: Sentinel hub | Landsat 8 | NASA FIRMS

Latest satellite images

Zao Volcano Maps

Below is a selection of maps showing the location and surroundings of the volcano at various resolutions based on aerial-imagery / terrain maps. Feel free to use them for non-commercial purposes on your blog or website as long as you credit them with a link back to this page (click to copy it).