21st November, 2013 Volcanic activity in Bonin Islands

Launched: November 26,2013
Last updated: November 07, 2016
On 21st November, due to volcanic activity, a new island emerged in Nishinoshima Isle, Bonin Islands of Tokyo.


 

7th November, 2016 Movie taken by the time of research on land


 

4th March, 2015
(Volcano research Center: Setsuya Nakada)
 
  • Activity of Nishinoshima on March 4, 2015 Observation time: 2:00 p.m.~2:30 p.m. and 6:10 p.m.~ 6:45 p.m. Fuel refilling at Iwoto Island.
    Aircraft used: Citation Encore of Asahi-Shimbun, “Asuka”
    Weather: clear and SW wind.

 Active volcanic eruption still continues at Nishinoshima, which started in late November of 2013. Until now, lava flows have extended into all directions from the base of the scoria cone located in the central south of the new land, expanding the area of lava plateau, almost engulfing the previous island (Nishinoshima).

During air inspection in this time, Strombolian explosions were repeated in the intervals of about ten seconds. Bombs and scoria landed on the slope of the scoria cone. Ash plume about 100 m from the crater changed its color from brown to white, drifting to northeast more than a few km (Photo 1). Lava flows were expanded their distribution area toward the east, entering to the ocean with steaming (Photos 1 and 2). New lava appeared on the surface about a few hundred meters before the ocean entry by breaking the colder crusts of older lava flows, and were moving directly to the ocean. The new lava flows are surrounded by dikes in the both sides and the flowing inside is darker (fresh; reddish in night) (Photos 3 and 4).

Photo 1: Easterly view of Nishinoshima. Strombolian explosions are repeated at the central scoria cone and dendritic lava flows extended radially but complexly from the base of the cone. In the eastern part, lava flows are entering to the ocean. Taken by from the Asahi-Shimbun aircraft by SN on the afternoon of March 4, 2015.
Photo 1: Easterly view of Nishinoshima. Strombolian explosions are repeated at the central scoria cone and dendritic lava flows extended radially but complexly from the base of the cone. In the eastern part, lava flows are entering to the ocean. Taken by from the Asahi-Shimbun aircraft by SN on the afternoon of March 4, 2015.
Photo 2: Close-up view of the eastern part of Nishinoshima. New lava flows, with lava dikes in the both sides and moving darker parts inside, are pouring to the ocean with steaming.Taken by from the Asahi-Shimbun aircraft by SN on the afternoon of March 4, 2015.
Photo 2: Close-up view of the eastern part of Nishinoshima. New lava flows, with lava dikes in the both sides and moving darker parts inside, are pouring to the ocean with steaming.Taken by from the Asahi-Shimbun aircraft by SN on the afternoon of March 4, 2015.
Photo 3: Night view of the scoria cone repeating the strombolian explosions and new lava flows pouring to the ocean. The latter were moving under the solid lava crust and appeared at the surface on half way to the ocean entry, implying the lava tube system of lava flowing.Taken by from the Asahi-Shimbun aircraft by SN on the evening of March 4, 2015.
Photo 3: Night view of the scoria cone repeating the strombolian explosions and new lava flows pouring to the ocean. The latter were moving under the solid lava crust and appeared at the surface on half way to the ocean entry, implying the lava tube system of lava flowing.Taken by from the Asahi-Shimbun aircraft by SN on the evening of March 4, 2015.
Photo 4: Close-up view of moving lava flows in the eastern part of Nishinoshima. Taken by from the Asahi-Shimbun aircraft by SN on the evening of March 4, 2015.
Photo 4: Close-up view of moving lava flows in the eastern part of Nishinoshima. Taken by from the Asahi-Shimbun aircraft by SN on the evening of March 4, 2015.
Photo 5: Strombolian explosion and hot bombs scattered on the slope of the central cone. Taken by from the Asahi-Shimbun aircraft by SN on the evening of March 4, 2015.
Photo 5: Strombolian explosion and hot bombs scattered on the slope of the central cone. Taken by from the Asahi-Shimbun aircraft by SN on the evening of March 4, 2015.

13th November, 2014

Volcanic eruption at Nishinoshima, showing continuous lava effusion to the north with repeating Strombolian events at the pyroclastic cone in the southern part:The original Nishinoshima island (yellow low land) still remains in a small part of the western part of lava field. Steam can be seen at the place where lava enters into the sea. Movies taken from above the island and near the sea surface by S. Nakada in the Asahi Shimbun Aircraft.

(Volcano research Center: Setsuya Nakada)
*Pictures are taken under favor of the Asahi Shimbun. For any citation, please contact Asahi Shimbun. 
*Click the image to see movie

  16th January, 2014
On the eruptive activity of Nishinoshima (further studies) Summary
The volcanic activity of the Nishinoshima is still active. Newly formed area, lava volume, discharge rate till 8th of January is summarized. The area is approx.650m EW, 550m SN, which is about 260000 m2: almost the same size as when a new island was at its maximum growth in the 1973-74 eruption (1 year after the emergence of the new island). The lava volume which flew into the ocean is more than 3×106 m3. The discharge rate is estimated to be still keeping approx.105m3/day or less. The change in discharge rate is important in order to predict the further volcanic activity, and should be closely observed continuously.
Area change of the new island
図1 西之島の新たに形成された部分の輪郭と面積変化.エラーバーは海岸線の読み取り精度から生じる誤差.2013年12月までは海上保安庁が公開している空撮写真および輪郭を参考にしているほか,2014年1月2日,8日はJAXAが公開している衛星画像,2013年12月17日までは国土地理院が公開している空撮写真,その他メディア等により報道されている空撮写真等も参考にしている.海底地形は海上保安庁水路部 (1993) ,旧西之島の輪郭は海上保安庁水路部1999年作成の地形図をもとにしている.
Fig.1 The profile and area change of the new island. The error bar is due to error in estimation of the coastline. Till December 2013, this is done by referencing the aerial photo and outline taken by the Japan Coast Guard, as well as satellite image published by JAXA for 2nd, 8th January 2014, and aerial photos taken by Geospatial Information Authority of Japan and press till 17th December. Bathymetric feature is based on the Hydrographic Department of the Japan Coast Guard (1993). The profile of former Nishinoshima is based on the topography, published in 1999 by the Hydrographic Department of the Japan Coast Guard.
      20140116fig2
Volume of lava flown into the sea and discharge rate
図2 海へ流出した溶岩体積とその変化※.エラーバーは,海岸線の読み取り誤差,海水面上の溶岩の比高と水深の不確かさから生じる誤差.なお,1月8日までの溶岩流出量は,前回の総噴出量のおよそ1/7に相当する.
Fig.2. The volume of lava flown into the sea and its development*. The error bar indicates the margin of error caused by uncertainty of relative elevation of lava on sea surface and water depth. The lava volume till 8th January is about 1/7 of the total volume of the previous eruption in 1973-74.
* Lava volume is estimated according to the difference between coast line it had before lava effusion (21st November), and the assumed water depth together with the distribution of lava flow on the sea-surface. Each time, there is a margin of error of 30%.
図3 期間毎の溶岩流出率とその変化※.エラーバーは,海岸線の読み取り誤差,海水面上の溶岩の比高と水深の不確かさから生じる誤差. Fig.3. Discharge rate of lava per period and its change*. The error bar indicates the margin of error caused by uncertainty of relative elevation of lava on sea surface and water depth.
*Discharge rate is estimated according to the difference between coast line it had before lava effusion, and the assumed water depth together with the distribution of lava flow on the sea-surface.
References
  • Japan Coast Guard Oceanographic Department http://www1.kaiho.mlit.go.jp/GIJUTSUKOKUSAI/kaiikiDB/kaiyo18-2.htm
  • Japan Coast Guard Hydrographic Department (1993) bathymetric geological survey report “Nishinoshima”, p. 47.
  • Geospatial Information Authority of Japan (information on Nishinoshima volcanic activity) :http://www.gsi.go.jp/gazochosa/gazochosa60010.htmlhttp://www.gsi.go.jp/gyoumu/gyoumu41000.html
  • JAXA Satellite Application and Promotion Center
  • http://www.sapc.jaxa.jp/topics/2014/news0110.html
(Volcano research Center: Fukashi Maeno)

On the eruptive activity of Nishinoshima Summary
Since the eruption off Nishinoshima, the new island kept growing and connected with the mainland Nishinoshima on 25th December 2013. Newly formed area, lava volume, discharge rate till 26th of December is summarized. The area is approx. 160000 m2, the lava volume which flew into the ocean is more than 2000000 m3. The discharge rate is estimated to be still keeping approx.105 m3/day. If this eruptive condition is still continuing, the newly formed part should be larger than the existing Nishinoshima by the time of January 2014. The change in discharge rate is important in order to predict the further volcanic activity, and should be closely observed continuously.
Area change of the new island
Fig.1. The profile and area change of the new island. The error bar is due to error in estimation of the coastline. This is done by referencing the aerial photo and outline taken by the Japan Coast Guard, as well as aerial photos taken by Geospatial Information Authority of Japan and press till 7th December. Bathymetric feature is based on the Hydrographic Department of the Japan Coast Guard (1993). The profile of former Nishinoshima is based on the topography, published in 1999 by the Hydrographic Department of the Japan Coast Guard.
Fig.1. The profile and area change of the new island. The error bar is due to error in estimation of the coastline. This is done by referencing the aerial photo and outline taken by the Japan Coast Guard, as well as aerial photos taken by Geospatial Information Authority of Japan and press till 7th December. Bathymetric feature is based on the Hydrographic Department of the Japan Coast Guard (1993). The profile of former Nishinoshima is based on the topography, published in 1999 by the Hydrographic Department of the Japan Coast Guard.
  20140110maeno_fig2
Volume of lava flown into the sea and discharge rate
Fig.2. The volume of lava flown into the sea and its development. The error bar indicates the margin of error caused by uncertainty of relative elevation of lava on sea surface and water depth.
Fig.2. The volume of lava flown into the sea and its development. The error bar indicates the margin of error caused by uncertainty of relative elevation of lava on sea surface and water depth.
Fig.3. Discharge rate of lava per period and its change*. The error bar indicates the margin of error caused by uncertainty of relative elevation of lava on sea surface and water depth.
Fig.3. Discharge rate of lava per period and its change*. The error bar indicates the margin of error caused by uncertainty of relative elevation of lava on sea surface and water depth.
※ Discharge rate (per day during the period) and lava volume is estimated according to the difference between coast line it had before lava effusion, and the assumed water depth together with the distribution of lava flow on the sea-surface (Ref. report on 8th Dec). Please note that the maximum estimation of the thickness of the lava flow is lowered from the previous reports, based on the 3D picture of the new island released by the Geospatial Information Authority of Japan on 3rd, 17th December. In accordance to this, the upper limit of the error bar for lava volume and discharge rate have changed, and therefore the estimation for before 20th December, is slightly lowered than the first estimation.
References
  • Japan Coast Guard Oceanographic Department http://www1.kaiho.mlit.go.jp/GIJUTSUKOKUSAI/kaiikiDB/kaiyo18-2.htm
  • Japan Coast Guard Hydrographic Department(1993) bathymetric geological survey report “Nishinoshima”, p. 47.
  • Geospatial Information Authority of Japan (information on Nishinoshima volcanic activity) :http://www.gsi.go.jp/gazochosa/gazochosa60010.html http://www.gsi.go.jp/gyoumu/gyoumu41000.html
(Volcano research Center: Fukashi Maeno)

Observed date/time: 26th December 2013, 12:30-13:00
Observer: Setsuya Nakada
Aircraft: The Mainichi Newspaper’s Cessna Citation CJ2+
Caption:The new volcanic island found on 20th November, continues discharging lava since 24th November, following vigorous explosions (phreatomagmatic events) due to interaction of magma with seawater. It jointed with Nishinoshima (older volcanic body) due to lava extension on 26th December 2013.
*Pictures are taken under favor of the Mainichi News Papers. For any citation, please contact the Mainichi Newspapers.
*Click the pictures to see movie
 20131227_nakada nishinoshima_movie2
(Volcano Research Center: Setsuya Nakada)

Growth process of the new island off Nishinoshima island (further study)
Summary Area, lava volume, discharge rate till 20th of December is summarized. As of 20th, the area is approx. 120000 m2, the lava volume which flew into the ocean is approx. 2×106 m3. The discharge rate is slightly increasing, however, is estimated to be still keeping approx.105 m3/day. The change in discharge rate is important in order to predict the further volcanic activity, and should be closely observed continuously.
Area change of the new island
図1 新島の輪郭と面積変化.エラーバーは海岸線の読み取り精度から生じる誤差.12月13日まで海上保安庁が公開している空撮写真および輪郭を参考にしているほか,12月7日までは国土地理院が公開している空撮写真,その他メディア等により報道されている空撮写真等も参考にしている.海底地形は海上保安庁水路部 (1993) ,西之島の輪郭は海上保安庁水路部1999年作成の地形図をもとにしている.
Fig.1. The profile and area change of the new island. The error bar is due to error in estimation of the coastline. This is done by referencing the aerial photo and outline taken by the Japan Coast Guard by 13th December, as well as aerial photos taken by Geospatial Information Authority of Japan and press till 7th December. Bathymetric feature is based on the Hydrographic Department of the Japan Coast Guard.
20131220nishinoshima_fig.2           図2 新島から海へ流出した溶岩体積とその変化※.エラーバーは海水面上の溶岩の比高と水深の不確かさから生じる誤差.
Fig.2. The volume of lava flown into the sea and its development. The error bar indicates the margin of error caused by uncertainty of relative elevation of lava on sea surface and water depth.
図3 期間毎の溶岩流出率とその変化※.エラーバーは海水面上の溶岩の比高と水深の不確かさから生じる誤差.
Fig.3. Discharge rate of lava per period and its change*. The error bar indicates the margin of error caused by uncertainty of relative elevation of lava on sea surface and water depth.
*Discharge rate (per day during the period) is estimated according to the difference between coast line it had before lava effusion, and the assumed water depth together with the distribution of lava flow on the sea-surface (Ref. fig 4 and report on 13th Dec). Please note that the maximum estimation of the thickness of the lava flow is lowered from the previous report, based on the 3D picture of the new island released by the Geospatial Information Authority of Japan. In accordance to this, the upper limit of the error bar for lava volume and discharge rate have changed, and therefore the estimation for before 7th, is slightly lowered than the first estimation.
図4 西之島から新島にかけての北西―南東方向の模式断面図(改訂版,12月20日時点)

Fig.4 cross-sectional diagram of Nishinoshima to the new island along the line of northwest to southeast (revised version, on 20th Dec.)

*It’s been a while since bathymetric chart is published in 90s, and so there are some possibility of shallow water area of 10 m depth have extended toward offshore by now (Erosion on the Nishinoshima main land is developing and materials are supplied on the southeast side). Also, hypothesis with slightly shallow water depth is also made, since there are possibilities of sedimentation at shallow water area before 20th November.

References

  • Japan Coast Guard Oceanographic Department http://www1.kaiho.mlit.go.jp/GIJUTSUKOKUSAI/kaiikiDB/kaiyo18-2.htm
  • Japan Coast Guard Hydrographic Department(1993) bathymetric geological survey report “Nishinoshima”, p. 47.
  • Geospatial Information Authority of Japan (information on Nishinoshima volcanic activity) http://www.gsi.go.jp/gazochosa/gazochosa60010.htmlhttp://www.gsi.go.jp/gyoumu/gyoumu41000

Observation from aircraft (20th Dec. 2013)
Observed date/time: 20th December 2013, 12:30-13:05
Observer: Fukashi Maeno
Aircraft: The Mainichi Newspaper’s Jet aircraft: “Kibou”
Summary
The volcanic activity of the new island off the southeast coast of Nishinoshima is still active with continuous Strombolian eruption and lava flow emission. Compared to how it was in early December, the new island is growing further from southwest to northwest with its size 450 m NS by 450 m EW (pic. 1, 2). Although there are no significant changes are found at the main crater, the height of the new island is estimated to be doubled and reaching around 40-50 m above sea level, due to pyroclastic cone growing again.
Main crater
Strombolian eruption is repeated every 10 to a few minutes at the main crater, and pyroclastic cone is growing (pic.3, 4). The new cone is growing on the partially collapsed crater, and its foot is extending on the lava flow at east side. Also, at the slope on the east side, there are at least 2 small vents and exploding with dark-brown plume, separately from the Strombolian eruption at the main vent (pic. 5).
Lava flows
Lava flow emission is continuing on the west side of the pyroclastic cone (pic. 1, 6). The flux of lava flow is mainly in 3 different directions: northwest, southwest and south east. Amongst them, the flux toward southwest is starting from relatively in a lower level. The water vapor caused by lava contacting the seawater is seen especially on the southwest, but it is occurring also on the northwest and southeast. Consequently, lava flux is all over on the west side, and this is considered to be increasing the area of the new island. The shortest distance to Nishinoshima is about 70 m, but the amount of water vapor in this area is a little. The distance between Nishinoshima and the actively moving part with lots of water vapors are approximately 100 m. On the other hand, the lava flow on the east side of the new island seems to be stopped, and partial erosion by the wave is recognized.
*Pictures are taken under favor of the Mainichi News Papers. For any citation, please contact the Mainichi Newspapers Co.Ltd.
写真1. 新島成長の様子.12月初旬以降,南西から北西側に大きく拡大し,西之島に接近している.南東から撮影.
Pic.1 Growth process of the new island. Since after early December, it is extending largely from southwest to northwest, getting closer to Nishinoshima. Picture taken from the southeast.   写真2. 新島成長の様子.褐色噴煙は火砕丘東斜面から上がっている.西から撮影.
Pic.2 Growth process of the new island. Dark brown plume is rising from the eastern slope of the pyroclastic cone. Picture taken from the west.
写真3. ストロンボリ式噴火が間欠的に発生し,再び火砕丘が成長している.海水面からの高さは,40-50 mと推定される.西側から撮影.
Pic.3. Strombolian eruption is occurring intermittently, and pyroclastic cone is growing again. The height is estimated to be 40-50 m above sea level. Picture taken from the west.
写真 4. 主火口付近の様子.マグマが見えている主火口(黄色矢印)のほかに,東側斜面に小火口が認められる(白矢印).写真奥は12月初旬までに東側に流出した溶岩.火砕丘はその上に裾野を広げている.西側から撮影.
Pic.4. Surroundings of the main crater. There is a small volcanic vent on the east side, other than the main crater where magma is seen. Lava that was discharged toward east by early December is at the back. Pyroclastic cone is spreading on top of them. Picture taken from the west.
写真 5. 火砕丘の東側斜面から立ち上がる褐色噴煙.斜面には小火口が少なくとも2箇所ある.北西側から撮影.
Pic.5. Dark brown plume rising from the eastern slope of pyroclastic cone. There are at least 2 small vents on the slope. Picture taken from the northwest.
写真 6. 火砕丘西側から流出している溶岩流.溶岩先端部では,高温の溶岩と海水との接触により蒸発した海水が激しく立ち昇っている.西から撮影.
Pic.6. Lava flowing from the west side of the pyroclastic cone. The leading end of the lava flow is entering into the ocean with vigorous white smoke. Picture taken from the west.

Growth process of the new island off Nishinoshima island (further study)

Summary on changes in lava volume and discharge rate of the erupting new island off Nishinoshima island by 13th of December (fig.1,2). The approximate volume of the lava and discharge rate (the discharge rate per day during the period) are estimated, according to the difference between oval shaped coast line it had before lava effusion, and the assumed water depth together with the distribution of lava flow seen on the sea-surface based on the aerial photos taken by the Japan Coast Guard (refer to fig.3 and previous reports).
図1 新島から海へ流出した溶岩体積とその変化.エラーバーは海水面上の溶岩の比高と水深の不確かさから生じる誤差.
Fig.1. The volume of lava flown into the sea and its development. The error bar indicates the margin of error caused by uncertainty of relative elevation of lava on sea surface and water depth.
図2 期間毎の溶岩流出率とその変化.エラーバーは海水面上の溶岩の比高と水深の不確かさから生じる誤差.
Fig.2 Discharge rate of lava per period and its change. The error bar indicates the margin of error caused by uncertainty of relative elevation of lava on sea surface and water depth.
図3 西之島から新島にかけての北西―南東方向の模式断面図
Fig.3. Cross-sectional diagram of Nishinoshima to the new island, seen from northwest to southeast. *Till 7th December, lava volume and discharge rate are determined referring to aerial photos by Geospatial Information Authority of Japan, as well as publications from other media.
(Volcano research Center: Fukashi Maeno)

13th December, 2013
Growth process of the new island off Nishinoshima island
Summary
Area, lava volume, discharge rate are estimated based on the aerial photos taken by the Japan Coast Guard and Geospatial Information Authority of Japan. The area of the new island increased up to 50,000 m2 by 4th December, and it is revealed that its growth rate is 8 times faster than the eruption that happened in 1973-74. The discharge rate of the lava is increasing over time, and is considered to be nearly 105 m3/day since end of November. This discharge rate is almost the same as the average discharge rate of the lava in Showa-Iwojima Island: ~1×105 m3/day (between January to March in 1935), the latest new island in our country excluding the previously formed Nishinoshima-Shinto. The changes in area and lava discharge rate by time lapse is important by means of estimating the further volcanic activity.
The process of formation
2013,
  • 20th November : Oval shaped new island extending northwest to southeast was found by the Japan Coast Guard, as well as discolored water. The eruption center is almost on the same location of the volcanic vents, where erupted in 1973.
  • 21st November: Phreatomagmatic eruption with cock’s tail jet (a typical Surtseyan eruption) is intermittently occurring. A pyroclastic cone is formed at the center of the island.
  • 22nd November: A new volcanic vent was formed on the east side. A lava flow was found (based on the aerial photos taken by the Japan Coast Guard)
  • 24th November: Strombolian eruption repeated from the volcanic vent at the summit, and the east side of the pyroclastic cone had partially collapsed in accordance with formation of a new volcanic vent and lava outflow. The lava flow with clinker has flown 50 m offshore on the east side.
  • 26th November: The new island enlarged as lava-flow on the east side kept spreading.
  • 1st December: Lava kept spreading toward east, forming number of lobes.
  • 4th December: The island spread on the southeast side with lava outflow.
  • 7th December: Lava outflow on the west side continued.

*There are no records of observation before 20th November, but it is inferred that there was a stage of eruption at the neritic, before reaching the sea surface. At the time of eruption in 1973, it took 5 months since recognition of discolored water, to become an island with pyroclastic cone, as we have now since 20th November. (Osaka, 1991)

Area change of the new island
The appearance of the new island is indicated in Fig.1, based on the aerial photos publicized on website of the Japan Coast Guard, Geospatial Information Authority of Japan, and other photos taken by media. Fig.2 shows the approximate area change of the new island. Defining the coast line is difficult and therefore, have margin of error. The island has been spreading since the outflow of the lava, and it was 50000 m2 on 4th December, 2 weeks since its initial eruption, and by 7th December, it had reached up to 60000 m2. By the 1973-74 eruption, it had taken 2 months to become larger than 50000 m2 (Osaka, 1991), and this time, it is growing 8 times faster.
Based on bathymetric chart (Japan Coast Guard, 1993), it is considered that the most part of lava flow, flew toward the east side where water depth gets deeper. It is considered that the direction of the lava flow, i.e. the growth direction of the island, has been affected by the bathymetric feature. Then afterward, lava changed its direction to southwest. This may be due to lava landfill and solidification on the southeast side, blocking the discharge, and had led the flow to choose a new fluid channel.
Fig.1. Growth process of the new island in Nishinoshima. bathymetric feature is by Japan Coast Guard Hydrographic Department (1993). The profile of Nishinoshima is based on the topography by the Japan Coast Guard Hydrographic Department in 1999.
Fig.1. Growth process of the new island in Nishinoshima. bathymetric feature is by Japan Coast Guard Hydrographic Department (1993). The profile of Nishinoshima is based on the topography by the Japan Coast Guard Hydrographic Department in 1999.
Fig.2 Area change of the new island. The error bar is due to error in estimation of the coastline. The analysis result of 7th December is derived by the Japan Coast Guard.
Fig.2 Area change of the new island. The error bar is due to error in estimation of the coastline. The analysis result of 7th December is derived by the Japan Coast Guard.
Lava volume and discharge rate
The eruption began approx.10-20 m deep, and by 4th December, it is estimated that the leading end of the lava flow had reached 25-30 m deep (fig.1).
The approximate volume of the lava (Fig.3) and discharge rate (the discharge rate per day during the period, Fig.4) are estimated, according to the difference between oval shaped coast line it had before eruption, and the assumed water depth together with the area of lava seen on the sea-surface.
The relative elevation of increased lava-flow on the sea surface is assumed to be 5 m (minimum)-15 m (maximum) in average, and also for the water depth, 5-10 m margin of error is taken into account.
The volume of lava flown into the sea is gradually increasing almost up to 1×106 m3. On the other hand, the ratio of lava outflow increased between 1st to 4th December, with average of 1×105 m3/day in 4 days, but is decreasing a little thereafter.
Fig.3 The volume of lava flown into the sea and its development. The error bar is the margin of error caused by uncertainty of relative elevation of lava on sea surface and water depth.
Fig.3 The volume of lava flown into the sea and its development. The error bar is the margin of error caused by uncertainty of relative elevation of lava on sea surface and water depth.
Fig.4 Lava outflow ratio per period and its difference. The error bar is the margin of error caused by uncertainty of relative elevation of lava on sea surface and water depth.
Fig.4 Lava outflow ratio per period and its difference. The error bar is the margin of error caused by uncertainty of relative elevation of lava on sea surface and water depth.
Comparison with Showa Iwo jima eruption in 1934-35
The average discharge rate of the Showa Iwo jima in Kagoshima Pref., the latest newly formed land in Japan other than Nishinoshima, was estimated to be ~1×105 m3/day during the period of lava outflow (2 months from January to March 1935) by the time of formation(Maeno and Taniguchi, 2006). The average ratio of lava outflow in Nishinoshima, is almost the same with average ratio of the Showa Iwo jima’s by the time it was formed.
*Note that these two erupting mechanism and outflow process of lava, can’t be simply compared since chemical composition in rocks of Nishinoshima and Showa Iwo jima are different (lava in Showa Iwo jima is dacite and rhyolite, on the other hand, lava in Nishinoshima is presumed to be andesite). However, I suppose that there is importance in comparing the basic physical quantity, such as eruptive volume and discharge rate.
Prospects
It is expected that lava will be outflowing and landfilling toward the west side as it is on the east. Also, after most of the surroundings of the new island will be filled with cooled and solidified lava, it is possible that a new volcanic vent will be formed by ascending magma, finding a new location where it is easy to explode. In this case, it is likely to have a phreatomagmatic eruption again, like we had on 20th November.
Further observation on the eruption is necessary, by paying close attention to lava outflowing location, direction, volume and ratio.
Referrence:
  • Data base of Hydrographic and oceanographic researches, the Japan Coast Guard: http://www1.kaiho.mlit.go.jp/GIJUTSUKOKUSAI/kaiikiDB/kaiyo18-2.htm
  • the Japan Coast Guard (report on Nishinoshima), p47
  • Geospatial Information Authority of Japan (information on Nishinoshima volcanic activity) http://www.gsi.go.jp/gazochosa/gazochosa60010.html
  • Maeno, F. and Taniguchi, H. (2006) Silicic lava dome growth in the 1934-1935 Showa Iwo-jima eruption, Kikai caldera, south of Kyushu, Japan. Bulletin of Volcanology, 68, 673-688.
  • Osaka Jouyo (1991), “Submarine volcanic activity in Japan sea” Tokai.university press, p. 279.
(Volcano research Center: Fukashi Maeno)

Observed date/time: 24th November 2013, 11:20-12:05AM
Observer: Setsuya Nakada
Aircraft: Asahi Shimbun’s Cessna (Citation Encore)
Summary
Condition of the new island haven’t changed much since 21st November afternoon when observed by the Japan Coast Guard, and it is still in an oval shape of approx.200m×100m extending from northwest to south east. The height of the new island is estimated as approx.20m high, just about the same height as the highest peak of Nishinoshima. On the northeast side, a lava landform sticking 50m out of the sea was found (pic.1 and 2). The island itself is in a trapezoidal shape and its surface is covered by rough volcanic bombs varying in sizes. On the other hand, on the southeast and southwest side, relatively smooth slopes covered by light brown volcanic ash develop from near the summit area, which suggest surface failure. (pic.2)
The eruption Around the volcanic vent in summit area
At the vent on the peak located southeast of the island center, strombolian explosion is repeated every few seconds to several tens of seconds. Volcanic plume and bombs are reaching up to 300-400m high and splashdowns within an area of 500m in the horizontal distance (pic.3). The vent size is becoming smaller (about 10m), with red-hot lava spouting out as it erupts, and its base is lava fountain of about 10m in height. Therefore, it is conceivable that a small lava lake is formed at the vent.
Lava flow in the northeast
There is also a small vent in the midst of the northeast slope of the summit vent. This vent spout volcanic ashes immediately after the explosion of the summit vent. Red-hot lava can be also seen in this small vent. A darker lava flow can be observed flown like a tongue from below the small vent to the coast line on the northeast side (pic.2b). This lava flow hits the relatively old lava at the coast line, and changes its direction toward the east, entering into the ocean with vigorous white smoke. This lava landform sticking out in the northeast, including the this lava flow tongue, is a part of the lava flow grown out from 21st, and the front had already been eroded partially.
*Pictures are taken under favor of the Asahi Shimbun. For any citation, please contact Asahi Shimbun. pic.1a.
Pic. 1a. Distant view of eruption of Nishinoshima and Shin-jima (new island). 24th November before noon. The new island repeating strombolian explosion. Aerial shot from the south east side of the Nishinoshima and the new island.
pic.1b.
Pic. 1b. Easterly view of eruption of Nishinoshima and Shin-jima. 24th November before noon. A white steam rising from the lava flow tongue that reached the ocean. Aerial shot from the southeast.
2a
Pic. 2a Northeasterly view of a small strombolian explosion on Shin-jima. Black lava flow streaming into the ocean.
Pic. 2b.
Pic. 2b. Easterly view of the lava flow entering the sea. A bank which develops on the right (north) side is probably made by the older lava flow. A brownish ashy cliffs develop on the slope in front (southeast) and behind (southwest) of the island top.
Pic. 3
Pic. 3 Westerly view of Shin-jima and ripples on the sea surface by volcanic bomb. Taken on 24th before noon.
Northerly view of Nishinoshima and Shin-jima taken from the aircraft flying about 50 m above the sea surface.
(Volcano Research Center: Setsuya Nakada)

We observed the 2013 activity of Nishinoshima volcano from an aircraft of the Asahi Shimbun, and recognized a pyroclastic cone was forming in the southeast of Nishinoshima isle.
Observation date/time: 21st November 2013, 9:13-9:31 (Observer/Kaneko)
Location: 400-500m southeast of the coastline of Nishinoshima (fig.1).
Size: major axis=300m, minor axis=100m (including ocean surface level)
Height: Approx.20-30m
Edifice: The pyroclastic cone is elongating along northwest-southeast direction, and has a vent in the southeast side of the center (major axis=100m) (fig.2). No lava flow is recognized.
Eruption state: Phreatomagmatic eruptions involving cock’s tail jet occur every 1-2 minutes (fig.2). The plume height is about 200-300m, however the white plumes eventually reach at the height of 900m.
Discolored water: Spreading to the southern side of the eruptive area(fig.3). No discolored area suggesting a new eruptive point is recognized.
*location and size have some ambiguity due to visual estimation. fig1. Location of active area 2013
Fig1. Location of active area 2013
*Pictures are taken under favor of the Asahi Shimbun. For any citation, please contact Asahi Shimbun. Fig.2 eruption with cock's tail jet (taken from the north side)
Fig.2 eruption with cock’s tail jet (taken from the north side)
Fig.3:Nishinoshima(1973-7Shinjima on the right)and eruptive area (white plume blows up)
(Volcano Research Center: Takayuki Kaneko)