Sakurajima volcanic crisis Aug 2015: news & updates

Volcano back to normal activity with regular vulcanian explosions

After 3 weeks with almost no or no significant explosions, the volcano seems to be back in its typical state of activity that has been going on for years (but been quite elevated during the past years in comparison): intermittent small to moderately sized vulcanian-type explosions from the Showa crater have resumed since 1 Sep, producing ash plumes that rose to heights of 5-9,000 ft (1.5 - 2.7 km) altitude.
PS: This is good news for our planned Volcano Special tour to Sakurajima from 26-30 Sep (spaces still available)...

Alert level lowered, no more deformation detected during 2 weeks

The alert level was downgraded back to 3 (out of 5) last Tuesday as signs of unrest and the risk of a sudden major explosion have decreased.
No rapid crustal movements have been detected since 17 August, suggesting that the inferred magma intrusion has stopped and is now stagnating & cooling instead of migrating further towards the surface.
The volcano continues to be unusually calm with only minor explosions and ash emissions occurring occasionally from the Showa crater.

Risk of major eruption might be decreasing

The likelihood of a feared larger eruption seems to be decreasing as the volcano has slowly been resuming small explosive activity and shots of the crater show the presence of fresh lava.
This could mean that the conduit is not as strongly blocked as feared and could allow the volcano to return to a more regular eruption style, where pressure is released more gradually.

Drone successfully shoots of magma from the crater of Sakurajima #volcano #Japan pic.twitter.com/q1AYyDxdsX c @sumomo_2 #travel

— Britannia PR (@Britanniacomms) August 22, 2015

According to the Meteorological Agency , 4 small eruptions were observed at Sakurajima early Sunday, shortly after midnight Saturday, around 2:30 a.m., past 3 a.m. and past 6 a.m., producing ash plumes that rose 300-600 m.
On Saturday, the Kagoshima Municipal Government lifted an evacuation advisory for areas around Sakurajima following a state-backed panel’s assessment Friday that the risk of an eruption seemed to be diminishing.
However, the volcanic alert level remains at 4 out of 5 as the crisis is not regarded over yet. Residents are asked to remain ready to evacuate quickly if need be.

Vent of Showa crater blocked - internal pressure rising

According to Japanese scientists, the scenario of a major eruption at the volcano is becoming more and more likely. The Asahi Shimbun news agency sent a drone to photograph the crater, confirming that a flat dome is currently blocking the conduit.
This blockage explains the near absence of explosions since mid July and suggests that internal pressure is increasing. The question is, simply put, when will it blow up and how much will come out?
Source: Blocked vent on Kagoshima volcano increasing likelihood of massive eruption (Asahi Shimbun)

Flat lava dome in summit crater

A pancake-shaped flat dome of lava has been detected inside the Showa summit crater. This type of dome is typical for moderately viscous and gas-poor lava (typically andesitic composition) extruded at subduction-zone stratovolcanoes.
The alert level of the volcano remains at 4 out of 5. One possibility is that the dome corresponds to older lava from the upper conduit that has been pushed out by a rising batch of fresher lava still inside the volcano.

Volcanic gas releases from sea floor detected

More worrying signs of volcanic unrest started to appear: according to FNN News, volcanic gas releases have been detected at the sea floor of the Futatsumata Port on the northern shore of Sakurajima peninsula (located approx 4 km from summit).

Sakurajima volcano (Japan): satellite radar measurments detect 16 cm inflation

The most recent radar measurements done by ALOS-2 satellite of the Japan Aerospace Exploration Agency (JAXA) show that the summit of the volcano has inflated by the enormous amount of approx. 16 cm during the interval 4 Jan - 17 August this year.
This suggests that a significant batch of new magma is currently stored in the volcano's upper plumbing system and the question remains when and how it might erupt. While surface activity at the volcano has remained very calm, authorities continue to prepare for the possible scenario of a major eruption in the near future.

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• The results of the emergency observation of Sakurajima by "ALOS-2" (JAXA)

Sakurajima volcano (Kyushu, Japan) activity update

Activity has actually decreased and been relatively low at the volcano during the past days. However, the risk of a major eruption remains according to the Japan Meteorological Agency who maintains alert level 4 (preparation for evacuation).

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Sakurajima volcano (Japan): alert level raised as volcanologist fear major eruption

Japanese volcanologist monitoring the volcano warned that a larger eruption could occur in the near future. The alert level of the volcano was raised to the second highest, 4 out of 5, meaning that preparations for evacuations of nearby areas (within a few km from the Showa crater) are in progress.
The alert was based on a strong swarm of shallow volcanic earthquakes located beneath the Showa crater. The seismic swarm started around 7 am on 15 Aug (local time), and peaked with almost 180 quakes per hour around noon. It gradually waned, but continues with weaker intensity until now.
At the same time, a significant inflation of the Showa crater has been detected. These both are likely caused by the rising of a new batch of magma, which could result in a larger-then-usual eruption.
While it is impossible to predict whether or not such an eruption will occur, authorities warn not to approach the crater within 3 km distance - a very moderate limit -, which is easily in the range of ballistic projectiles and pyroclastic flows that likely occur during a larger eruption.

• Alle News zu: Sakurajima Vulkan
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• 桜島 火山性地震が急増 警戒レベル4に (NHK news)