An expedition to confirm the presence of underwater hazards was carried out in Halmahera waters, Indonesia, to the west of Halmahera Island from August to September 2021. The expedition carried out a multibeam survey, surface-towed magnetic survey, and seafloor sampling. A ~ 615-m-tall conical feature with traces of hydrothermal activity was discovered. The feature is bounded on the southeastern (SE) side by a series of normal faults at the peak, with possible dextral strike-slip faults traced west of the feature. The feature displays the potential presence of volcanic rocks based on the observed contrasting magnetic anomaly signature of down to − 100 nT, which at the magnetic equator corresponds to the presence of highly magnetised material. Four 2.5-D magnetic models were built to test various scenarios on the subsurface structure of the feature, mainly focusing on the presence of volcanic rocks at different epochs and a possible presence of serpentinisation. X-ray diffraction (XRD) of the silt and clay sediments sampled confirms traces of late-stage hydrothermal activity, indicated by a high percentage of quartz (53.87%), followed by calcite (34.56%), kaolinite (6.54%), and illite minerals (5.04%). Non-carbonate materials are yet to be found in the sampled sand and gravel sediments, which mainly consist of shell and coral fragments. The discovery of the conical feature, now termed the Yudo Sagoro Hill, provides new information on the structure and activities on the seafloor of Halmahera waters.

中文翻译：

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在印度尼西亚哈马黑拉水域发现圆锥形特征：晚期热液活动的痕迹

2021年8月至9月，在印度尼西亚哈马黑拉岛以西的哈马黑拉海域进行了一次确认水下危险存在的考察。该考察进行了多波束勘测、水面拖曳磁力勘测和海底采样。发现了约 615 米高的圆锥形特征，带有热液活动的痕迹。该地物的东南 (SE) 侧以一系列位于峰顶的正断层为界，在该地物的西侧可能存在右旋走滑断层。该特征根据观察到的低至 − 100 nT 的对比磁异常特征显示火山岩的潜在存在，该特征在磁赤道处对应于高磁化材料的存在。建立了四个 2.5 维磁性模型来测试该特征地下结构的各种情况，主要关注不同时期火山岩的存在以及可能存在的蛇纹石化。对淤泥和粘土沉积物取样的 X 射线衍射 (XRD) 证实了晚期热液活动的痕迹，石英百分比很高 (53.87%)，其次是方解石 (34.56%)、高岭石 (6.54%) 和伊利石矿物（5.04%）。采样的砂砾沉积物中尚未发现非碳酸盐物质，主要由贝壳和珊瑚碎片组成。这个圆锥形特征（现在被称为 Yudo Sagoro 山）的发现提供了有关哈马黑拉水域海底结构和活动的新信息。