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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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Host Rock: 
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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"
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.