xxx volcanAzuma volcano is a group of small stratovolcanoes, shield volcanoes, domes and cinder cones in NE Honshu, Japan, west of Fukushima city.
Historical eruptions were mostly small phreatic eruptions from the Issaikyo volcano at the northern end of the Higashi-Azuma volcanic complex.
The beautiful symmetrical Azuma-Kofuji crater and a nearby fumarolic area at southeast slope containing the 200 m wide Oana crater are the most prominent features of Issaikyo volcano and along with Goshiki-numa and Oke-numa crater lakes popular tourist destinations.
Oana crater has produced several phreataic eruptions in recent decades and contains very powerful fumaroles, producing plumes rising several hundred meters high.
Introduction:The Azama volcanic complex is mostly basaltic to andesitic in composition and forms two E-W aligned rows. It is one of the active volcanoes at the volcanic front of the Northeast Japan arc. Older andesitic cones were built more than 30,000 years at the western end. Volcanic activity has migrated from W to E over time, and the Higashi-Azuma volcano group at the eastern end are the youngest.
The recent craters are concentrated within a NW-SE trending, 3-km-long, and 1-km-wide zone through Jododaira; Goshikinuma, Issaikyo, Issaikyo-minami, Oana, Tsubakurosawa, Iwotaira-minami, Kofuji, and Okenuma craters from north to south.
There are at least 5 magmatic unit and 7 phreatic ones and were produced during eruptions including Vulcanian explosions. More than 99% of the magma had erupted from Kofuji crater.
adapted from: Y. Takahiro (2005) "Eruptive history of Azuma volcano, NE Japan, during last 7,000 years: Stratigraphy and magmaplumbing system of the Azuma-Jododaira products.", Journal of the Geological Society of Japan, v. 111 (2), pp 94-110
2008 eruption and new fumarole
A new fumarole producing a plume rising a few 100 m appeared at the northwestern rim of Oana crater of Azuma volcano on 11 Nov 2008 and new mud deposits including lithic fragments were found around the new fumarolic crater.
Japanese scientist measured the fumarolic gases and found high concentrations (2.3-3.0%) of SO2 and temperatures of up to 475 deg C.
(Shin’ya Onizawa, Hiroshi Shinohara, Nobuo Matsushima: "Appearance of a new fumarole in November 2008 and related mud deposits in Azuma volcano" JPGU Meeting 2009 poster abstract)
2001 seismic activity increases
An small swarm of earthquakes occurred beneath Azuma during May 2001, peaking between 21-22 May when 51 volcanic tremors were measured in total, out of which 33 were felt by residents.
(GVP monthly reports)
1996 and 1998 tremors
Small volcanic earthquakes and slight volcanic tremor were detected above background levels in 1996 and 1998.
An eruption occurred on 7 December 1977, after earthquakes had begun in September 1977, followed by spattering ejection of mud and sand and small blocks in October. Active fuming was seen in November. It produced an ash plume rising 500-1,000 m above the crater and causing minor ashfall. Similar ash ejections occurred sporadically through January 1978.
(GVP monthly reports)
1893 eruption and fatalities
An phreatic explosion from Issaikyo crater west of Oana killed 2 geologists who were hit by falling stones.
(NOAA National Geophysical Data Center, Significant Volcanic Events)
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