Tongatapu) is a recent puffer, and the other is Kavachi seamount on the south west of Honiara in the Solomons (pic left).
Kavachi is a regular eruptive volcano either beneath the surface or just above. It is regarded as very active and maritime charts show that a wide berth is given to the south. Yeah just the sort of mission for a drog to dabble in. As the Coxn on HMNZS Tui in 1992 (the only drog onboard) I was given an HI (Hydrographic Instruction) to do a spot survey of Kavachi volcanic cone and surrounds, We were in Honiara for the 50th Anniversary of Guadalcanal, so a packed weekend of activities and some R&R, then we sailed Monday for a quick overnight steam to Kavachi.
The equipment to be used let's say was basic nonetheless, and coupled with untrained survey assistants (ships co volunteers) made for a very interesting process. To make it even more difficult the CO had put a 36 hour time limit to do the work. I gave all the volunteers a rush around on the Kelvin Hughes echo sounder and the hand held portable Satnavs and Honda Hand Held Sonar Torches (used for divers for underwater work) and used with the inflatable over the shallows. I guess that left me the Raytheon Deep Echo Sounder and plotting in the chart room..
Having briefed the CO, we started our task with vigour and after a 3 hour box search had managed to delineate three cones. The northern one required a rapid back down and inflatable was deployed which resulted in spot depths of 5 metres. Happy we had it covered and convinced no submarine activity moved on to the second cone to the south and east of this to Cone Two. This cone was a very volcanic cone shape (Fuji-like) and after a few hours we deduced this wasn't active. With darkness approaching we tackled the third cone, well not so much a cone more a convoluted peak vent. We approached this one from the south and at slow speed. The depth to seaward started at around 3000 metres and rose steadily past 1500 metres. Then it shot up and peaked as we reversed at 8 metres. The CO came and said that was close and I had a wry smile (pooped). We decided to drop the inflatable into the water and found the depth at highest was 2metres. And the water was boiling and the thermometer suggesting 50+ degrees.
Having got as much of this cone done, we worked through the night south and west of that cone to ensure there were no other submarine volcanoes which there weren't. Having done a 36 hour straight shift and same for some of the crew and the CO, we retired to our pits after a top scran, job well done. BZ to tech staff, sonarmen, and those also that helped.
And finally. This thing blows without any warning. Just imagine that after reading this :)
Editted 14/3/2018 an Undersea Volcano.
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Japanese survey ship lost surveying an Undersea Volcano.