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The 2017 Nishinoshima Eruption: Combined Analysis Using Himawari

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The 2017 Nishinoshima Eruption: Combined Analysis Using Himawari Kaneko et al. Earth, Planets and Space (2019) 71:140 https://doi.org/10.1186/s40623-019-1121-8 FULL PAPER Open Access The 2017 Nishinoshima eruption: combined analysis using Himawari-8 and multiple high-resolution satellite images Takayuki Kaneko1* , Fukashi Maeno1, Atsushi Yasuda1, Minoru Takeo1 and Kenji Takasaki2 Abstract Nishinoshima volcano suddenly resumed eruptive activity in April 2017 after about 1.5 years of dormancy since its previous activity in 2013–2015. Nishinoshima is an uninhabited isolated island. We analyzed the eruption sequence and the eruptive process of the 2017 eruption (17 April–10 August: 116 days) by combining high-temporal-resolution images from Himawari-8 and high-spatial-resolution images from the ALOS-2, Landsat-8, and Pleiades satellites. We used these data to discuss how temporal variations in the lava efusion rate afected the fow formations and topographical features of the efused lava. The total efused volume was estimated to be 1.6 107 m3, and the aver- age efusion rate was 1.5 105 m3/day (1.7 m3/s). Based on variations in the thermal anomalies× in the 1.6-μm band of Himawari-8, which roughly× coincided with that of the lava efusion rate estimated by ALOS-2, the activity was segmented into fve stages. In Stage 1 (17–30 April: 14 days), the lava efusion rate was the highest, and lava fowed to the west and southwest. Stage 2 (1 May–5 June: 36 days) showed a uniform decrease in fow, and lava fowed to the southwest and formed the southwestern lava delta. During Stage 3 (6–15 June: 10 days), the lava efusion rate increased in a pulsed manner, the fow direction changed from southwestward to westward, and a narrow lava fow efused from the southern slope of the cone. In Stage 4 (16 June–31 July: 46 days), the lava efusion rate decreased and lava fowed westward through lava tubes, enlarging the western lava delta. Around the end of July, lava efusion mostly stopped. Finally, in Stage 5 (1–10 August: 10 days), explosive eruptions occurred sporadically. The variation in lava efusion rate seemed to play an important role in forming diferent fow patterns of lava on Nishinoshima. In Stages 1 and 3, lava fowed in multiple directions, while in Stages 2 and 4, it fowed in single direction, probably because the efusion rate was lower. A pulsed increase in the lava efusion rate during Stage 3 caused new breaks and disturbances of the lava passages near the vents, which resulted in changes in fow directions. Diferences in the size of lava lobes between the southwestern and western deltas are also considered to result from diferences in the lava efusion rate. Keywords: Himawari-8, LAVA FLOW, Volcano, Nishinoshima, Thermal anomaly, Remote sensing Introduction formed a new volcanic island (Fig. 1c). In the 2017 activ- Nishinoshima volcano, located in the Ogasawara Islands ity, lava efusion continued for about 4 months, and the in the western Pacifc (Fig. 1a), suddenly resumed activ- areas from the southwest to the west of the island were ity (Phase 2) in April 2017 after about 1.5 years of dor- covered with lava fows (Fig. 1d) (further, a small erup- mancy since the 2013–2015 eruption (Phase 1), which tion occurred in 2018—Phase 3). Te activities at Nishi- noshima are a rare case of volcanic island formation in *Correspondence: [email protected] the ocean (Maeno et al. 2016) and furthermore are an 1 Earthquake Research Institute, The University of Tokyo, 1-1-1 Yayoi, important opportunity to observe the process of lava Bunkyo-ku, Tokyo 113-0032, Japan fowage and the eruption sequence of a volcano built up Full list of author information is available at the end of the article by successive layers of numerous lava fows. © The Author(s) 2019. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creat iveco mmons .org/licen ses/by/4.0/. Kaneko et al. Earth, Planets and Space (2019) 71:140 Page 2 of 18 a b N A B C Chichijima Island D Nishinoshima 0 200 km 21 Apr 2017 c 25 Jul 2016 d 28 Aug 2017 W-delta SW-delta 500 m 500 m Fig. 1 a Location of Nishinoshima (reproduced from Google Maps). b Aerial view of the cinder cone and the northern vents taken from the northwestern side on 21 April 2017 (provided by Asahi Shimbun). c Nishinoshima after the 2013–2015 eruption (25 July 2016) (Geospatial Information Authority of Japan). d Pleiades image of Nishinoshima after the 2017 eruption (28 August 2017) Unfortunately, a geological survey of the activi- Landing for surveying was performed once in October ties was difcult, as Nishinoshima is an uninhabited 2016 long after decline of the 2013–2015 activity, but isolated island located 1000 km south of Tokyo, and it was only a 3-h stay (Takeo et al. 2018). Geophysical 130 km west of the nearest inhabited island, Chichi- research was conducted by observing seismic activity jima (Fig. 1a). During the active periods, access to with ocean-bottom seismometers installed about 4 km areas within 4 km of the island was strictly prohibited. ofshore from the island (Shinohara et al. 2017) and Kaneko et al. Earth, Planets and Space (2019) 71:140 Page 3 of 18 also by a seismometer installed in the island in Octo- and topographical features of the efused lava fows, as ber 2016 (Takeo et al. 2018), which was destroyed by interpreted from the high-resolution images. the 2017 eruption. However, continuous or system- atic observation of island surface activity could not be Outline of the Nishinoshima activities carried out, and only aerial observations and images Te edifce of Nishinoshima volcano has a conical shape released by governmental agencies (e.g., the Japan with a height of about 3000 m above the adjacent seafoor Coast Guard (2019) or Geospatial Information Author- (Japan Coast Guard 2019). Te island of Nishinoshima ity of Japan (2018)) or media were available for exam- is the summit of this volcano that projects above the sea ining the eruptive conditions. Meanwhile, Maeno et al. surface (the original Nishinoshima). Te frst historic (2016) investigated the morphology of the lava fows eruption occurred in 1973–1974 in the ocean at a loca- efused in the frst 15 months of the 2013–2015 erup- tion adjacent to this island, and the edifce grew gradually tion using a series of Terra SAR images, and these and fnally joined the original Nishinoshima (Aoki and revealed the eruption sequence and rheological char- Ossaka 1974; Ossaka 2004). After this activity ended, the acteristics of the lava fows, which demonstrated the majority of the edifce was eroded by sea waves. About usefulness of satellite images for observing an isolated 40 years later, a new activity—the 2013–2015 (Phase 1) island in the ocean. However, the 2017 and 2018 erup- eruption occurred at about the same place as the previ- tions still remain uninvestigated. ous one. Te eruption began in the shallow ocean in Volcanoes are widely distributed in various areas on November 2013 and was followed by the subaerial efu- the earth, and some of them are located in remote areas sive activity involving Strombolian eruptions. Finally, a where access is difcult. Tus, remote sensing with satel- volcanic island with a diameter of approximately 2 km lites is becoming a common means of observing remote was formed by the end of 2015 (Maeno et al. 2016, 2018) locations. Lately, the spatial and temporal resolutions of (Fig. 1c). According to Maeno et al. (2016), lava fowed satellite images have been signifcantly improved com- down the slope and branched into several smaller lobes pared to those available in the 1980s (e.g., Francis and in a dendritic manner. Te edifce grew gradually through Rothery 1987; Rothery et al. 1988; Glaze et al. 1989), as these lava fows piled up around the cinder cone. when they were frst applied to volcano observations. We Lava initially fowed down as an open-channel fow, have worked on developing a combined analysis for erup- but over time as the surface solidifed, fows continued tive activities that uses satellite images with high tempo- through lava tubes formed below the solidifed surface ral resolution (e.g., Himawari-8) and multiple satellites layer. When the lava efusion rate was high, lava fowed that provide images with high spatial resolution and dif- through large open channels with a length of several hun- ferent properties (e.g., images obtained with synthetic dred meters. Te average efusion rate was estimated to 5 3 3 aperture radar (SAR), infrared images, and extremely be about 2.0 × 10 m /day (2.3 m /s). high-spatial-resolution (< 1 m) images). Tis approach Te 2017 Nishinoshima eruption (Phase 2) was frstly has enabled us to obtain detailed information about noticed on 20 April 2017 (JST) by routine observation eruption sequences and processes (Kaneko et al.
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