Mount Bandai (Bandaisan) is a volcanic complex formed by several overlapping andesitic stratovolcanoes.  The largest of these is Obandai, topping out at 1,816 m.  The most recent large eruption was in 1888, when Kobandaisan peak collapsed to the north.  Viewed from the S, Bandaisan is a conical profile, often called the Fuji of Fukushima Prefecture or Mount Fuji of the North.  The view is much different from the N, where much of the N side of Kobandaisan is missing, creating a debris avalanche that buried multiple villages and formed several large lakes. 

Bandaisan is considered currently active and is surrounded by Bandai – Ashai National Park, created in 1950, and the Bandai-san Geopark est 2011.  The volcano was originally called Iwahashi – yama (A Rock Ladder to the Sky in the local language).  It is sometimes called Aizu Fuji and Aizu Bandai.  The S foot is called Omotebandai.  The N foot is called Urabandai.  It is on the list of the 100 famous mountains in Japan, and one of the top 100 geographic landmarks in Japan. 

The closest towns are Inawshiro Town, 16.000, Bandai Town, 3,900 and Kitashiobara Village, 3,300.  The Bandai – Ashai National Park – Bandaisan got nearly 5.5 million visitors in 2010.  There were over 85,000 mountain climbers in 2010.  Major park facilities include Kitashiobara, Mt Bandai Eruption Museum, and the Urabandai Visitor Center. 

There are a pair of smallish ski areas on the S flank of Bandaisan and a much larger one on the S flank of neighboring Nekoma.  Local economy is based on tourism and agriculture.  Climate is described as a humid continental climate with warm summers and cold winters with heavy snowfall.  Average highs in August are just below 24° C, with lows -2° C.  Average precipitation is 137 cm/year, with September being the wettest month. 

The Enichi Temple is located on the SW foot of Bandai.  The temple served a central role in mountain worship.  It is surrounded by mountains where people come to worship, Mount Bandai to the NE, Mount Mayadake to the N, and Mount Azuma to the N.  It was established in 807 AD, a year after a large Bandai phreatic eruption.  Some people think there is a connection between the eruption and the foundation of the temple.  There are several routes for visiting Azumayama Shrine established originating from the main temple of the Enichi shrine.  There are seven climbing routes on Mount Bandai. 

As with the rest of Japan, volcanic activity at Bandaisan will be reported by the Japan Meteorological Agency (JMA).  It is monitored with multiple instruments.  There is an active webcam available. 

Region

Volcanoes are thick in this portion of Honshu, with most of them being in the vicinity of Bandaisan, E, W and S.  Our previous post on Chokai extensively used the JMA Catalog of the Active Volcanoes in Japan (Fourth Edition), and JMA maps of the region.  As with Chokai, the JMA maps depict much more extensive volcanism.  Most of these systems are not considered to be active and will be mentioned only in passing. 

Note the two different numbering systems used by the JMA National Catalog and the Maps.  The National catalog are typically two-digit numbers, while the Maps list volcanoes as DXX, with a two-digit number following a “D” prefix.  There are links to more detailed descriptive JMA products for individual volcanoes in both the catalog and map. 

We will instead use the Volcano Discovery list of quaternary volcanoes in Japan as our source.  Due to the large number of volcanoes in this portion of Japan, we will limit our review to volcanoes within 50 km of Bandaisan.  Note that volcanoes in this region generally erupt andesites to basaltic andesites, though rhyolites and dacites are associated with the caldera forming eruptions.  All distances will be measured from Bandaisan. 

Nekoma 

 The 1,404 m Nekoma volcano (Map D65) is located some 6 km WNW of Bandaisan.  It is called the Brother volcano to Bandai.  It was active 1.1 – 0.35 Ma.  The volcano is constructed of thick andesitic lava flows and domes.  There are substantial block and ash flows associated with dome extrusion.  A horseshoe shaped collapse caldera is at the summit.  Small domes extruded into the caldera following the collapse.  The volcano built in three stages starting 1.1 Ma, followed by 800 – 600 ka and 450 – 350 ka.  Caldera collapse took place somewhere at or before 450 ka.  The caldera is 3 km in diameter with a lake on the W side. 

Adatarayama   

Adatarayama and Azumayama are two recently active volcanoes located 18 – 21 km E and NE of Bandaisan respectively.  There are several other volcanoes in the immediate region that are not recently active.  The JMA map product lists them as Sasamori Yama, Nekomagatake and Aizu Nunobiki Yama.   

Adatarayama (Catalog 035, Map D63) is a 1,728 m andesitic – basalt andesitic group of stratovolcanoes and domes located some 18 km E from Bandaisan.  The high point is Minowasan, a dome-shaped stratovolcano.  Currently active Numanotaira has a 1.2 km wide summit crater surrounded by hot springs and fumaroles.  It is breached by the Iogwa (Sulfur) River to the W.  Historic eruptions all came from Numanotaria crater.

Construction of the complex took place in three stages, 550, 350 and 220 ka.  The main volcanic activity here began with large pyroclastic flow discharges.  Activity at Kimenzan 550 – 450 ka.  Maegadake activity began 350 ka.  The main volcanic chain Minowasan – Oshozan was formed 250 ka.  Magma discharge rate was highest during this period.  120 – 30 ka small magmatic discharges took place repeatedly in intervals 20 – 10 ka.  Starting 10 ka, magmatic and phreatic eruptions took place repeatedly.  The most recent magmatic eruption took place 2.4 ka. 

The most recent episode of tremor took place in 1995.  It was followed by a small, aseismic phreatic eruption Sept 1996.  Four hikers were killed in a gas-filled depression Sept 1997.  

Azumayama 

The Azumaayama volcanic group (Catalog 034, Map D62) is a cluster of stratovolcanoes, shield, lava domes and pyroclastic cones located some 21 km NE from Bandaisan.  The andesitic to basaltic complex was constructed in two E – W rows W of Fukushima City.  Activity migrated E, with the Higashi – Azuma volcano group being the youngest.  The system tops out at 1,949 m. 

The group is spread over a 25 x 15 km area, long axis E – W.  Many of the volcanoes in the N chain have summit craters.  Many of these craters have crater lakes.  There are many new pyroclastic cones and craters near Issaikyozan in the E.  Historic eruptions were explosions in and around the Oana crater.  There is a large fumarole field across its S and E flanks. 

Higashi – Azuma has multiple volcanic cones.  It was first active 300 ka.  A sector collapse forming a horseshoe shaped amphitheater, 2 km wide open to the E took place 280 – 100 ka.  Activity after the collapse created Azuma – Kofuji and Okenuma within the caldera. 

Smithsonian GVP lists the most recent eruption as a small ash ejection Jan 1978.  Phreatic activity continued through Feb.  Small amplitude volcanic tremor was detected April, May and July 1996.  There was a small increase in seismicity late May 2001 with 33 felt earthquakes.

Zao  / Okama 

The Zaozan (Zao Zan, Zaosan) (Catalog 33 / Map D58) volcanic group is considered to be the most active of N Honshu.  It is a complex of stratovolcanoes topping out at 1,841 m, located some 67 km NNE from Bandaisan.  The Ryuzan volcano forms the W group (Nishi-Zao).  Byobu and Fubo volcanos form the S group (Minami-Zao).  Basement granite is relatively high at 1,500 m and the stratovolcanoes are relatively small.    The 7 km3 Zaozan volcano forms the central group (Chuo-Zan).  The complex is topped by several lava domes and the Goshikidake tuff cone. 

There have been multiple collapse events producing debris avalanches during the Pleistocene.  The currently active Okama crater is located on top of Goshikidake.  It has a strongly acidic crater lake (Goshikinuma).  The post caldera Goshikidake pyroclastic cone has been active over the last 2,000 years. 

Initial activity took place 1 Ma – 700 ka.  There was a dormant period of 300 ka.  Renewed activity 400 – 100 ka erupted andesitic lava flows from multiple eruption centers.  Peaks from these centers make up the upper half of the edifice.  Kumanodake and Kattadake are the highest peaks.  Caldera formation took place 30 ka, creating a 2 km caldera at the summit.  At the same time, explosive activity erupting basaltic andesite began and continued intermittently until the present.

Smithsonian GVP lists 43 eruptions over the last 9.6 ka.  There was a single VEI 4 300 AD.  Other than that, most of the listed eruptions are VEI 2-3.  The most recent listed eruption was 1940, a small phreatic eruption.  There have been multiple instances of earthquakes, changes in fumarole activity, rumbling and earthquake swarms since then.  The most recent of these was 1995.

Aoso is a 820 m andesitic to dacitic stratovolcano on the SE end of the Zao massif, 71 km NE from Bandaisan.  It was active 400 – 300 ka and is constructed in an older caldera. 

Sunagohara 

The rhyolitic Sungohara caldera and lava dome are located E of the Numazawa caldera, some 24 WSW from Bandaisan.  Size of the caldera is difficult to find, but shows up on Google Maps as an elliptical crater around 2 km on it longest axis.  It is nested in the much larger Iriyamazawa Formation deposited in a 20 x 15 km caldera.  The system was active 290 – 220 ka.  The Sunagohora – Kubota tephra is 4 km3 of pumice fall and pyroclastic flow deposits erupted 220 ka.  Fall and flow deposits are around equal in volume. 

Numazawa 

Numazawa is a 2 km wide caldera nested within an older caldera, some 30 km WSW from Bandaisan.  It erupted dacite to rhyolites.  Eruption of the 110 ka rhyolitic Shibahara pyroclastic fall and the 71 ka dacitic Mukuresawa lava dome were followed by the dacite Plinian Mizunuma eruption 45 ka.  Emplacement of the Sozan dome took place in 43 ka and 20 ka.  The Numazawako pumice flow and Plinian eruption 4.6 ka created the current caldera, now filled with a caldera lake. 

Aizu Nunobiki 

Aizu Nunobiki (Aizu Nunobiki – yama) is a 1,108 m andesitic to dacitic stratovolcano located some 32 km S of Bandaisan.  It was active 1.4 Ma.

Futamata 

Futumata (Futumata yama) is a 1,544 m stratovolcano and lava dome located some 41 SSW from Bandaisan.  It dates 140 – 90 ka.  A thick lava flow extends NW.  The volcano is located withing the recently active Tonohetsuri caldera.  The Narioka caldera cuts the W rim of Tonohetsuri and the W rim of the older Ono caldera.  These calderas produced the Kumado, Ashino and Nishigo pyroclastic flows 1.4, 1.2 and 1.0 Ma respectively. 

Nasu 

The Nasudake volcanic group is cluster of stratovolcanoes and domes constructed on the N end of the Kanto Plain, 55 km SSW from Bandaisan.  The group is generally aligned N-S.  Volcanic activity here has been active for 500 ka.  Initial activity built three large basaltic to dacitic stratovolcanoes.  This was followed by construction of three more smaller stratovolcanoes.  One of the smaller stratovolcanoes collapsed 40 – 30 ka, producing the massive Ofujisan debris avalanche deposit.  This covers a broad are SE of the volcano. 

The youngest stratovolcano started building 16 ka.  Six magmatic eruptions took place over that time.  The most recent of these 1408 – 1410 AD, extruding the summit dome.  These eruptions produced block and ash flows and ended with lava flows.  Smaller phreatic eruptions took place every few hundred years during the past 5 ka.  The most recent of these was 1963.  Earthquake swarms and seismic activity were recorded in 1977, 1985 and 1996.

Bandaisan (Bandai) Volcano

Bandaisan (Catalog 036, Map D64) is a complex formed of four overlapping stratovolcanoes rising above the N shore of Lake Inawashiro and Inawashiro Town.  The highest point, Obandai is 1,816 m.  The four coalescing stratovolcanoes created four peaks, Mount Obandai, Mount Kobandi, Mount Akabane, and Mount Amidagamine.  The greater edifice was Fuji-shaped before 1888.  Flank collapse during that eruption significantly changed the N face of the volcano.  Note that earlier eruptions also changed the shape of the volcano. 

Typical activity from Bandai includes flank collapses and debris avalanches.  Bandaisan has not experienced a magmatic eruption in the last 10 ka.  Activity can be divided into multiple phases starting around 290 ka, when there were a pair of scoria eruptions.  Earlier activity in the region was at neighboring Mount Nekoma 1.1 – 0.35 Ma 6 km to the W.

I

Activity at Bandiasan is divided into two stages, old and new.  These are separated by a period of inactivity.  Old stage activity built Akahaniyama and Kushigamine.  Activity in the new stage built Kobandisan which collapsed in the 1888 eruption and Obandaisan. 

It is unclear when activity started, but the volcano was in place by 290 ka.  Two scoria eruptions took place 290 ka.  Here the eruption narratives diverge a bit.  Either there were several more scoria and pumice eruptions 210 – 200 ka followed by eruptions of ash and pumice 165 – 145 ka, or there was a hiatus in activity starting 250 ka resuming with a Plinian eruption 80 – 70 ka. I have found nothing as yet that reconciles the diverging dates.

Either way, New Stage activity resumed with the Hayama 2 Plinian eruption 80 – 70 ka.  This eruption broke up the shape of the mountain.  The Kobandai cone was formed by Vulcanian eruptions and extrusion of andesitic lava flows on the N slope of the old volcanic cone around 50 ka. 

The Hayama 1 Plinian eruption took place around 40 ka and produced the Okinajima debris avalanche.  This was caused by intrusion of dacite into the old stage volcanic cone, similar to the 1980 eruption of Mount St Helens.  The Okinajima debris avalanche and pumice flow deposits were emplaced at the S foot of the volcano.  The Ojinajima pyroclastic flow was followed by the Zunashi pyroclastic flow.  These dammed the river flowing through the Inawashiro basin, creating Lake Inwashiro.  Following a short pause, Vulcanian explosions and andesitic lava flow extrusions refilled the collapse crater, forming the Obandai volcanic cone. 

 The last magmatic eruption took place over 25 ka.  Since then, there have been four major phreatic eruptions in the last 5 ka.  The most recent of these were 806 and 1888 AD. 

Eruptions

The most recent magmatic eruption took place 9.4 ka and produced a tephra fall.  This was followed by four more phreatic eruptions 8.3, 7.0, 6.6 and 5.8 ka.  All of these produced tephra falls.  The 5.4 ka phreatic eruption produced the Kosuizawa debris avalanche from the Biwazawa upstream area.  There were two more phreatic eruptions 5.4 and 2.7 ka.  The second of these produced lahars.  Flank collapse 2.7 ka was associated with the Obandaisan E collapse wall and SE side of Kobandaisan, producing the Biwazawa debris avalanche.

The 806 AD phreatic eruption produced a tephra fall from the old crater n the E side of Obandaisan.  There was reported rumbling in 1643 and 1655 and possible eruptions in 1719 and 1787.  The subsequent phreatic eruption 1888 will be covered in more detail below. 

Bandaisan has been active since 1888.  Rumbling was reported in 1897.  There were a pair of small crater wall collapses / debris avalanches in 1938 that extended 3 km.  These killed two, injured 5 and swept away / damaged four homes.  Multiple chunks of the 1888 crater wall collapsed in April 1954.  Earthquakes, seismic swarms and volcanic tremor were reported in 1987, 1988, 2000 and 2001.  Smithsonian GVP carries a final report of volcanic tremor Jun 2012, first since Jun 2009.  There appears to be a break in reportage or the ability to translate 2005 – 2012. 

1888 Phreatic Eruption

The 1888 phreatic eruption was notable as it was driven by the rupture and collapse of the pressurized hydrothermal system beneath the volcano.  It was remarkably wet and cool, though it did result in a flank collapse of Kobandai to the N.  There are multiple popular accounts of the eruption.  A two-part set of articles in More Than Tokyo is a good place to start.  Part 2 on recovery can be found at the link.  Noah Oskow writing in Unseen Japan, Jun 2019 has a similar piece. 

The July 15, 1888, eruption began with small felt earthquakes on the N foot of the volcano 8 – 10 July.  Intensity increased to moderate earthquakes 13 – 14 July.   The main eruption began immediately after three earthquakes starting 0700 15 July.  The first of these was so small that many locals did not feel it.  The next two were much stronger.  There was no observed anomaly at hot springs and fumaroles in the summit region at the time. 

At the third of these quakes, a M 5 at 0745, an eruption began at fumaroles 100 m upslope from the Kaminoyu hot spring resort on the flank of Kobandai.  15 – 20 explosions took place over the first minute, sending a black plume over a kilometer high.  The last explosion discharged a horizontally moving cloud to the N.  Within 10 minutes of the explosions, the debris avalanche descended to the N foot and the pyroclastic flow swept over the E flank of the volcano.

The main explosive eruption lasted for only a few minutes, but thundering sounds lasted for the next couple of hours.  The plume rapidly rose to at least 5 km, causing darkness.  It also poured a heavy, warm rain which lasted for 5 minutes.  Everything in the fallout area was covered with a bluish-gray sticky coating.

A secondary debris stream traveled through the Biwasawa Valley.  It just reached the village of Mine, burying half the houses.  Prevailing winds distributed fallout from the cloud SE with a light ash reaching the Pacific Ocean 120 km from the volcano.  The plume had mostly reduced by 0900 and ash falls stopped by 1600. 

Failure of the N part of Kobandai peak produced the debris avalanche.  It covered 34 km2 with an estimated volume of 1.5 km3.  The avalanche eroded an avalanche valley, a box canyon on the N flank and deposited numerous hummocky hills on N of the volcano.  It moved relatively quickly and traveled in waves.  Maximum runout was 11 km.  The collapse created a 1.5 km wide, 800 m deep horseshoe crater exposing hydrothermally altered rock in the lower part of the crater wall. 

Initial violent explosions lasting a minute or so produced the pyroclastic flow.  The flow blew down thousands of trees below the volcano, many more than a meter in diameter.  The main branch of the flow cascaded for at least 6 km along Biwazawa Valley, overlapping the 2.5 ka Biwazawa debris avalanche.  Some villages were destroyed by the winds from the pyroclastic flow.  There is a N directed lobe documented via eyewitness accounts that has not been further described. 

The 1888 eruption is notable by the sudden and short duration of its climax.  The eruption and flank collapse were triggered by seismic shocks without significant precursors and the main explosions ceased within a very short time.  Ejected material does not have any juvenile magma, indicating an explosive interaction between magma and the underground hydrothermal system.  There was no sign of ascent of new magma into the edifice, no subsequent volcanic phenomena after sector collapse unloaded the magmatic system.  The leads to the conclusion that the 1888 eruption was caused by a sudden expansion of steam within the edifice.

How so?  Fumarole activity at the summit had been vigorous up until the eruption.  Hydrothermal activity within the edifice was stored in a self-sealing fracture system.  Earthquake shocks commonly disrupt self-sealed systems, triggering phreatic eruptions.  It appears that this sealed system was disrupted by the final earthquake at 0745 L.  The 1888 collapse event is similar the previous event 2.5 ka, generating the Biwazawa debris avalanche and phreatic fall deposits. 

Steep topography right is the E rim of the 1888 collapse scarp of Koandican.  Two lakes in the distance formed after the avalanche blocked local river drainages.  Caldera walls expose stratigraphy of the cone with pyroclastic deposits interlayered with lava flows.  Image courtesy L Siebert, 1988 via Smithsonian GVP

These sorts of phreatic collapses are believed to have happened at Ritter Island, 1888, Papandayan, 1772, and Iriga, 1628.  All of these start and end with the paroxysmal phase.  Intense earthquakes can cause massive volcanic landslides without explosive eruptions, Unzen, 1792.

 The eruption was the first major disaster faced by the newly formed Japanese Red Cross.  The lake district formed by the eruption is now known as Urabandai or Bandai – kogen and became a popular tourist destination.

Tectonics

Tectonics of N Honshu are driven by the subduction of the Pacific Plate beneath the Okhotsk Plate at the Japan Trench E of Honshu.  The Okhotsk Plate is a wedge-shaped minor tectonic plate that extends N to include all of the Kamchatka Peninsula, and W to mainland Siberia.  It S end is in the vicinity of Tokyo, bounded by the Philippine Sea Plate offshore and the Amur Plate to the S and W.  In many places, this is described as the North American Plate.  As tectonics here is driven by subduction, the region is prone to megathrust earthquakes, the most recent of these being the M9.0 2011 Tohoku earthquake.

One of the interesting things about this particular subduction margin is the distribution of volcanic centers.  Normally, volcanic systems are randomly distributed along active plate margins.  Volcanoes here have formed in conspicuous groupings.  Recent volcanic systems are about 50 km wide and spaced with 80 km gaps.  This line is parallel with the Japan Trench.  The descending Pacific Plate is perhaps 150 km beneath the volcanic front.

Conclusions

While it has been a while since the last magmatic eruption at Bandaisan, it has been phreatically active over the last 10 ka.  Eruptions are typically explosive.  The edifice is well altered, with a vigorous hydrothermal system.  The volcano and surrounding region are thick with hot springs.  There is a heat source, an unstable mountain, and an established, vigorous hydrothermal system.  Its immediate region is also thick with active volcanoes, meaning there should be no shortage of new magma.  There is no reason to believe activity at Bandaisan will decrease in the future.

Additional information

Bandai, Honshu, Japan, Volcano, Oregon State University

Pyroclastic density current from the 1888 phreatic eruption of Bandai volcano, NE Japan, Yamamoto, et al, Jun 1999

Geomorphological development of Bandai volcano, I Moriya, 1988

Directed volcanic blasts, GS Gorshkov

Aspects of the landscape of Bandai-san before the eruption, F Yonechi, 1988

A new hypothesis on the collapse of the Bandai-san volcano in 1888, Y Fuimo, Dec 1987

Study on fault system within Bandai-san explosion caldera of 1888 year using VLF-EM method and radioactivity prospecting, Imaisumi, et al, 1995

Blast and debris-avalanche deposits of the 1888 eruption, Bandai volcano, Nakamura and Glicken, 1988

Rockmagnetic study on the debris avalanche deposits of Banda volcano, Sakai & Inokuchi, May 2003

Brief outline of Bandaisan, D Shimozura, 1988

Characteristics of Bandai-san volcano – an overview by landsat data, Birdeye picture and stereographic contour maps with special reference to antient debris avalanche, Inokuchi, et al, 1988

Geology of Bandai volcano and its volcanic history, K Mimura, 1988