Suwanosejima


Suwanosejima volcano forms one of the central islands of Tokara volcanic archipelago which is part of the Ryukyu ark to the south of mainland Japan. The island lies approximately 200km to the south of Kagoshima and nearby Sakurajima volcano and has a summit elevation of 799m. It essentially consists of four volcanic bodies oriented in a N-NE direction over a length of 9km. Eruptions in historic times have involved basaltic-andesitic / andesitic lavas. It is noted that the volcanic bodies are sometimes referred to as volcanoes in their own right.


Suwanosejima Map Suwanosejima volcano, night eruption O-take crater, Sakuchi caldera

Suwanose Island map

Volcanic activity in the Ryukyu ark is the result of subduction of the Kyushu-Palau Ridge area of the Philippine Sea Plate beneath the Eurasian plate (Mashima 2009. J. Volc. Geotherm Res. 186, p.195-209). The subducting plate is at a steep angle in the area and is roughly at a depth of 80km under Suwanosejima, which lies about 120km to the WNW of the plate boundary.

Significant eruptions were recorded in 1813-1814 and 1884-1885. The island was deserted for about 70 years after the "Bunka Eruption" of 1813-1814, which led to deposition of significant amounts of tephra over much of the island, including the residential areas, and the eruption of two andesitic lava flows from the SW crater, which extended as far as the W coast. The eruption resulted in abandonment of the settlements and the island remained uninhabited for the following 70 years. At the end of the eruption, a sector of the volcano comprising the NE summit crater "Otake" collapsed, creating a large debris avalanche and forming the Sakuchi Caldera which extends as far as the E coast. The 1884-1885 eruption was less powerful, yet also resulted in effusion of lava, known as the Meiji lava, which reached the E coast.

Eruptive activity in recent times has been largely characterized by frequent but moderate scoria eruptions, yet studies on an exposed 60m sequence of tephra beds at the south end of the island concluded that a 3m thick rhyolitic pumice deposit and overlying 15m thick pyroclastic flow deposit had a source vent on the island (Moriwaki et al. "Quaternary Tephra Layers of Suwanose Island in the Tokara Islands, South Japan"). These deposits are more than 23000 years old as they are overlain by AT-ash which was from a massive eruption of the Aira Caldera (encompassing modern day Sakurajima) at around this time. This shows that the volcano has erupted with a much greater magnitude than in historical times in the more distant past.


Suwanosejima, Negimadake crater Suwanosejima, Negimadake crater

Suwanose Island, view from SSW, Nabedau crater on left

Suwanosejima, Nabedau crater, view from ENE

Suwanosejima fissure region Suwanosejima Bunka Crater

Suwanosejima, fissure region between Tongama, Otake craters

Suwanosejima, Bunka Crater, view from SE

Suwanosejima, volcanic bomb covered in ash Suwanosejima volcano, plant covered in ash

Suwanosejima, lava bomb covered in fresh ash

Suwanosejima, plant coated in ash

Suwanosejima volcano, degassing O-take crater, Sakuchi caldera Suwanosejima volcano, night eruption O-take crater, Sakuchi caldera

Suwanosejima, Sakuchi Caldera

Suwanosejima, nighttime view, Sakuchi Caldera

From 1957 to 1994 and since 2000, Suwanosejima has frequently displayed explosive strombolian-vulcanian eruptions from the NE summit crater Otake (On-Take), which is located within the Sakuchi Caldera. These are relatively similar to eruptions of Semeru volcano but are much less frequent, with periods between eruption usually ranging from several weeks to as little as hours during phases of heightened activity. The mechanism of eruptions, in particular the accompanying macroscopic inflation and deflation of the edifice, has been compared at Suwanosejima, Sakurajima and Semeru (Iguchi et al., 2008. J. Volc. Geotherm Res. 178, p.1-9). The explosive activity is weaker than at Sakurajima, with air-shock amplitudes ranging from 10-180 Pa at a distance of 3.3km. Projectiles usually fall well short of a km from the crater and ash clouds rarely exceed 1km in height. The active vent formed by a merging of the adjoining 1994 and 2000 vents and lies about 0.5km from the Caldera rim.

The onset of explosions is preceeded by an precursory inflation about 100 secs beforehand. The pressure source has been localized to a depth of about 100m below the crater and correlated to a volume change of about 150 cubic meters. The actual explosion event starts with the release of volcanic gas from the plug overlying the vent just seconds before the cap is destroyed and expelled in the form of volcanic bombs. Release of sulpur dioxide gas actually declines about 3 min before eruptions at Suwanosejima as gases build up just beneath the cap. Once gas pressure exceeds the restraining capacity of the cap, gas is briefly expelled resulting in a decrease in upper conduit pressure and a corresponding brief dilation of the conduit. This causes rapid degassing and expansion of the water-saturated magma in the conduit (notably at a depth of 0.5 km before occuring at shallower depths), which drives magma explosively out of the conduit and expells the cap.


Minor Vulcanian Eruption followed by Sustained Ash Venting (Onset at approx.16:45, Dec. 29, 2009):


Suwanosejima volcano, vulcanian eruption, O-take crater, Sakuchi caldera Suwanosejima volcano, ash eruption, ash cloud, O-take crater, Sakuchi caldera Suwanosejima volcano, ash eruption, ash cloud, O-take crater, Sakuchi caldera


Suwanosejima volcano, ash eruption, ash cloud, O-take crater, Sakuchi caldera Suwanosejima volcano, ash eruption, ash cloud, O-take crater, Sakuchi caldera Suwanosejima volcano, ash eruption, ash cloud, O-take crater, Sakuchi caldera


Suwanosejima volcano, ash eruption, ash cloud, O-take crater, Sakuchi caldera Suwanosejima volcano, ash eruption, ash cloud, O-take crater, Sakuchi caldera Suwanosejima volcano, top of ash column, O-take crater, Sakuchi caldera


The activity observed on Dec. 29-30, 2009 apparently differs from that described above. The volcano was in a state of almost continuous mild strombolian activity driven by continuous noisy degassing, this being sporadically interrupted for at most a few seconds. Small vulcanian events (accompanied by visible pressure waves) occurred in small clusters every 3-5 hours with each individual explosion separated by 15-30 min (for example, the sustained eruption at approx. 16:45 on 29. Dec. was preceeded by at least 3 other vulcanian events with the last two being 27 and 45 min prior to the main event). The last explosion in each series led into a sustained phase of increased activity lasting for several minutes and resulting in an at least 2 km high ash column. This was followed by a phase of intense degassing before the background strombolian / mild degassing activity was resumed.


Minor Vulcanian Eruption followed by Sustained Ash Venting (Onset at approx. 19:40, Dec. 29, 2009):


Suwanosejima volcano, vulcanian explosion, night eruption O-take crater, Sakuchi caldera Suwanosejima volcano, night eruption, ash venting, O-take crater, Sakuchi caldera

Vulcanian Explosion

Sustained Ash Venting

Suwanosejima volcano, night eruption, ash, strombolian activity, O-take crater, Sakuchi caldera Suwanosejima volcano,glowing gas cloud, night eruption O-take crater, Sakuchi caldera

Ash, Gas venting, strombolian activity at base

Intense degassing, gas cloud lit by strombolian activity within

Further Nighttime Images:


Suwanosejima volcano, incandescence dawn, O-take crater, Sakuchi caldera Suwanosejima volcano, night degassing, strombolian activity, O-take crater, Sakuchi caldera

Suwanosejima, view at dusk

Fumarolic activity, vent degassing, strombolian activity

Suwanosejima volcano, nighttime vulcanian eruption O-take crater, Sakuchi caldera Suwanosejima volcano, nighttime strombolian eruption O-take crater, Sakuchi caldera

Minor Vulcanian explosion (approx. 00:35, Dec.30, 2009)

Close-up strombolian activity

Suwanosejima volcano, ash cloud rising after small vulcanian eruption, night eruption O-take crater, Sakuchi caldera Suwanosejima volcano, ash cloud rising after small vulcanian eruption, night eruption O-take crater, Sakuchi caldera

Ash cloud rising after 00:35 explosion

Ash cloud rising after 00:35 explosion

Access Information


Suwanosejima island is inhabited by about 50 persons. No shops are found on the island although there are three small traditional guest houses. A camping site is also available. The island is served by ferry from Kagoshima but we experienced problems with significant short-term timetable changes. Permission to climb Suwanosejima must be obtained from the park administration on the island. In Jan. 2010, public access was permitted to within 1km of the crater, or 500m before the Caldera rim. This is due to the significant risk of ballistics. Electrical discharges from ash-clouds to the rim may also be a hazard since the build-up of static electricity could clearly be felt on the rim during eruptions.

A pathway formerly led through the vegetated portions of the flanks to a height of about 400m where the thick vegetation stops. The path has however been abandoned and is severely eroded in places. Further, it is overgrown with thick, often chest-deep vegetation which makes it difficult to find and extremely arduous to climb. Once above the vegetation, the climb is relatively simple but rough in places. No marked path is visible . A warning sign marks the edge of the no-go area at the summit.


Suwanose Island

Morning silhouette of Suwanose Island viewed from SW. Tondachi-dake on left, other craters aligned in center.

Suwanose Island shrouded in ash Tokara ferry leaving Suwanose Island

View N over SE dock, note ashfall

Tokara ferry departing, note ashfall top right

Suwanose Island Abandoned Track

View from campsite, note minor ash emission

Eroded steps and vegetation covering remains of path



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