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Name Alias(es): 
Volcano O
Niua Tahi
Caldera "O"
Target "O"
Northeast Caldera
North East Lau Caldera
MTJ-1 caldera
MGDS_FeatureID lowest in hierarchy: 
Vent Sites: 
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Notes on Vent Field Description: 
off-axis caldera, lying between the Northeast Lau Spreading Center (NELSC) and the northern Tofua arc; 15-km diam caldera with central cone Motutahi; SS11/2004 cruise: "the most spectacular retrieval of massively altered and sulfide-bearing lithologies was from Target O."; magnetic data also suggests active hydrothermal field (Kwak et al. 2006); Merle et al. (2008): tow t08c15; "Directly east of the NELSC the seafloor is dominated by an impressive circular volcanic caldera named Volcano “O”. Backscatter data acquired during our bathymetric surveys showed that Volcano O is the source of several lava flows covering large areas of the seafloor. Our plume surveys showed that Volcano O is also host to several active hydrothermal vents." (; Resing et al. (2010) indicate that this site may be confirmed active as of May 2009 ROV Jason II: "Observations of hydrothermal activity at two sites were made within the caldera at Volcano “O”"; May 2010 NOAA cruise report camera tow: "In response to the discovery of a very intense sulfur-rich plume over the dacite cone in the SE corner of Volcano O, Tow 8 found concentrated venting of sulfur near its summit at ~1280 m"; Baker et al. 2019: sites 41 and 42 in Table 2;
Year and How Discovered (if active, visual confirmation is listed first): 
2009 ROV Jason II; 2003 plume only; 2004 dredging (SS11/2004 cruise); 2005 plume only; 2008 commercial ROV (report does not confirm activity)
Discovery References (text): 
cruise report NoToVE-2004, SS11/2004,, accessed 28 May 2015;
(plume only) Kim, J. et al. (2009) Venting sites along the Fonualei and Northeast Lau Spreading Centers and evidence of hydrothermal activity at an off-axis caldera in the northeastern Lau Basin. Geochemical Journal 43: 1-13;
(deposits only), accessed 28 May 2015: Tunu-Sosisi SMS;
SRK Consulting report for Nautilus Minerals,, accessed 28 May 2015;
Resing, J. A., et al. (2010) Hydrothermal Activity and its Chemical Characteristics in the NE Lau Basin. AGU Fall Meeting Abstract #T13B-2187;
Other References (text): 
(magnetics) Kwak et al. 2006 AGU Fall Meeting abstract #T51B-1529;
Arculus "Arc-backarc systems of northern Kermadec-Tonga" (;
Merle, S., et al. (2008) Northeast Lau Basin, R/V Thompson Expedition TN227, November 13-28, 2008, Apia to Apia, Western Samoa. Cruise report. Accessed 8 May 2015,;
Embley et al. (2009) Extensive and Diverse Submarine Volcanism and Hydrothermal Activity in the NE Lau Basin. AGU Fall Meeting abstract #V51D-1719;
Baker ET, Walker SL, Massoth GJ and Resing JA (2019) The NE Lau Basin: Widespread and Abundant Hydrothermal Venting in the Back-Arc Region Behind a Superfast Subduction Zone. Front. Mar. Sci. 6:382. doi: 10.3389/fmars.2019.00382;