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Article Abstract

An expedition to the Kavachi submarine volcano (Solomon Islands) in January 2015 was serendipitously timed with a rare lull in volcanic activity that permitted access to the inside of Kavachi’s active crater and its flanks.  The isolated location of Kavachi and its explosive behavior normally restrict scientific access to the volcano’s summit, limiting previous observational efforts to surface imagery and peripheral water-column data.  This article presents medium-resolution bathymetry of the main peak along with benthic imagery, biological observations of multiple trophic levels living inside the active crater, petrological and geochemical analysis of samples from the crater rim, measurements of water temperature and gas flux over the summit, and descriptions of the hydrothermal plume structure.  A second peak was identified to the southwest of the main summit and displayed evidence of diffuse-flow venting.  Microbial samples collected from the summit indicate chemosynthetic populations dominated by sulfur-reducing ε-proteobacteria.  Populations of gelatinous animals, small fish, and sharks were observed inside the active crater, raising new questions about the ecology of active submarine volcanoes and the extreme environments in which large marine animals can exist. 

Supplementary Materials

Figure S1.  Bathymetric map of Kavachi and the summit crater (inset, lower right) showing locations of single-beam echosounder returns used to create the plot (black dots).  See the Methods section for a detailed description of how the bathymetric data was processed. 
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Video S1.  Edited highlights of a baited autonomous camera dropped into the summit crater of Kavachi.  The entire descent from 0-50 m depth is shown, followed by representative clips of the reef fish, sharks, and gelatinous zooplankton that were observed.  Note the distinct orange coloration and high turbidity of seawater inside the crater at depth. 
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Burd, B.J., and R.E. Thomson.  2015.  The importance of hydrothermal venting to water-column secondary production in the Northeast Pacific.  Deep Sea Research Part II 121:85–94, https://doi.org/​10.1016/​j.dsr2.2015.04.014.