Morphological evidence of an explosive eruption event in October 2023 at Sofu Seamount in the Izu-Bonin Arc

IF 2.6 3区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Marine Geology Pub Date : 2024-09-24 DOI:10.1016/j.margeo.2024.107405

Hiroki Minami , Kenichiro Tani

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引用次数: 0

Abstract

Sofu Seamount is one of the poorly studied submarine edifices in the Izu-Bonin Arc. There is no known historical record of volcanic activity, thus its eruptive history and volcanic features are completely unknown. However, on October 9, 2023, at least 14 T-phases originating near Sofu Seamount were observed. An 80 km-long raft of floating pumice was observed off Sofu Seamount on October 20. These spatially and temporally coherent observations indicate that an eruption occurred from a deep seafloor vent somewhere near Sofu Seamount. In order to investigate the origin of this submarine eruption, we collected new bathymetric data in 2024 and compared it with older bathymetric data collected in 2022, 2007 and 1987. The bathymetric comparison revealed evidence for explosive eruptions at Sofu Seamount between 2022 and 2024. During this time, a crater, 1.6 km wide and 400 m deep, was formed at the pre-existing central cone on the western part of Sofu Seamount, whose pre-eruption summit depth was 737 m. The maximum negative depth change was 451 m and a volume of 430 × 10⁶ m³ was removed due to the crater formation. A dome-like structure, 1 km wide and 100 m high was constructed northeast of the crater, part of which collapsed as a result of the crater formation. The volcanic products were transported over 6 km downslope and emplaced on the adjacent seafloor where positive depth changes up to 75 m were observed. Landslides also occurred around the crater. The largest slide on the northern flank formed a slide scar that is 3.8 km long and 1 km wide. Here, the maximum negative depth change was 148 m and 140 × 10⁶ m³ of material was removed. The slide materials were deposited downslope where positive depth changes up to 61 m were observed. Considering the occurrence of the earthquake swarm on October 2–8, 2023 and T-phase swarm on October 9, the timing of the eruption can be constrained within October 2023.

An analysis of volcanic and tectonic morphology reveals a distinct tectonic influence on volcanism at Sofu Seamount. Sofu Seamount is located in a back-arc rift zone where the N–S trending Torishima and Sofu Rifts have formed. The new bathymetric data showed that the rifts have an asymmetric structure and can be divided into two segments, which are identified here as inner and outer rifts. The inner rifts are bounded by steeper fault scarps that have experienced more subsidence than the outer rifts. The western part of Sofu Seamount, where the eruption occurred, is located within the inner rifts, and is heavily dissected by rifting-related normal faults, while the eastern part is located outward of the inner rifts and is not dissected by faults. The October earthquake swarm was more concentrated in the area of the inner rifts and some large earthquakes showed normal fault focal mechanisms with a tension axis approximately in E–W direction. Our morphological observations combined with recent seismic events show that the inner rifts are the currently active tectonic structures and young volcanism at Sofu Seamount is controlled by the back-arc rifting of the Izu-Bonin Arc.

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伊豆-波宁弧区 Sofu 海山 2023 年 10 月爆发事件的形态学证据

索福海山是伊豆-波宁弧区研究较少的海底建筑之一。由于没有已知的火山活动历史记录，因此其喷发历史和火山特征完全不为人知。不过，在 2023 年 10 月 9 日，观测到至少有 14 个 T 相从 Sofu Seamount 附近发源。10 月 20 日，在索孚海山附近观测到一个 80 公里长的浮石筏。这些时空连贯的观测结果表明，索孚海山附近的某个深海海底喷口发生了喷发。为了研究这次海底喷发的起源，我们收集了 2024 年的新测深数据，并与 2022 年、2007 年和 1987 年收集的旧测深数据进行了比较。水深测量对比显示，索孚海山在 2022 年至 2024 年期间曾发生过爆炸性喷发。在此期间，索孚海山西部原有的中心圆锥形成了一个宽 1.6 千米、深 400 米的火山口，火山爆发前的顶点深度为 737 米。在火山口东北方向形成了一个宽 1 公里、高 100 米的圆顶结构，其中一部分由于火山口的形成而坍塌。火山产物向下迁移了 6 千米，并沉积在邻近的海底，在那里观察到深度变化达 75 米。火山口周围也发生了滑坡。北侧最大的滑坡形成了一条长 3.8 公里、宽 1 公里的滑痕。这里的最大负深度变化为 148 米，140 × 106 立方米的物质被清除。滑坡物质向下沉积，在此观察到的正深度变化达 61 米。考虑到 2023 年 10 月 2 日至 8 日发生的地震群和 10 月 9 日发生的 T 相地震群，可以将喷发时间限制在 2023 年 10 月。索孚海山位于弧后断裂带，N-S 向的鸟岛断裂带和索孚断裂带在此形成。新的水深数据显示，裂谷具有非对称结构，可分为两段，在此被确定为内裂谷和外裂谷。内侧裂谷以陡峭的断层疤痕为界，比外侧裂谷经历了更多的沉降。发生喷发的索孚海山西部位于内裂谷内，被与断裂有关的正断层严重剖切，而东部则位于内裂谷外侧，没有断层剖切。10 月份的地震群更多地集中在内侧裂谷地区，一些大地震显示了张力轴大致位于东西方向的正断层聚焦机制。我们的形态观察结果与最近的地震事件相结合，表明内裂谷是目前活跃的构造结构，索孚海山的年轻火山活动受伊豆-波宁弧后弧裂谷的控制。

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来源期刊

Marine Geology 地学-地球科学综合

CiteScore

6.10

自引率

6.90%

发文量

175

审稿时长

21.9 weeks

期刊介绍： Marine Geology is the premier international journal on marine geological processes in the broadest sense. We seek papers that are comprehensive, interdisciplinary and synthetic that will be lasting contributions to the field. Although most papers are based on regional studies, they must demonstrate new findings of international significance. We accept papers on subjects as diverse as seafloor hydrothermal systems, beach dynamics, early diagenesis, microbiological studies in sediments, palaeoclimate studies and geophysical studies of the seabed. We encourage papers that address emerging new fields, for example the influence of anthropogenic processes on coastal/marine geology and coastal/marine geoarchaeology. We insist that the papers are concerned with the marine realm and that they deal with geology: with rocks, sediments, and physical and chemical processes affecting them. Papers should address scientific hypotheses: highly descriptive data compilations or papers that deal only with marine management and risk assessment should be submitted to other journals. Papers on laboratory or modelling studies must demonstrate direct relevance to marine processes or deposits. The primary criteria for acceptance of papers is that the science is of high quality, novel, significant, and of broad international interest.