Lobster
Lau Basin, Tonga, SW Pacific Ocean
15.333°S, 176.283°W; reported depth -1,500 m (seamount)
All times local (Fiji Standard = UTC + 12 hours)
Hydrothermally active submarine volcano found in 2008
The Australian Commonwealth Scientific and Industrial Research Organization (CSIRO)
announced in press releases that several large active submarine volcanoes, spreading ridges, and
rift zones had been discovered in the Northwest Lau back-arc basin, NE of Fiji Island (figure 1).
The discoveries were made by a team of Australian and American scientists aboard the CSIRO
Marine National Facility Research Vessel Southern Surveyor in Spring 2008 (CSIRO, 2008a).
While mapping previously uncharted areas for submarine volcanic and hot spring activity, the
team located several volcanoes, one of which they named Lobster. The depth of Lobster is given
as 1,500 m in the InterRidge Vents Database [Ver. 3.1] (2013). The location of Lobster is shown
in figure 1, based on coordinates given in Lupton and others (2012). The base maps in figure 1
came from Keller and others (2008), a study primarily discussing the area in the rectangle on the
larger map. The sea floor was mapped with multibeam sonar. Lobster is located ~75 km NNW
of Niuafo’ou volcano/island and ~680 km NE of Suva, Fiji (figure 1). Dugong volcano lies ~60
km E of Lobster.
Figure 1. Two maps showing (lower left) North Island, New Zealand (in black) and selected
plate tectonic features along the Kermadec and Tonga trenches (hachured line with teeth on
upthrown side) and (larger map) Lobster (white square) and other features such as the main
spreading centers, geographical features, and subaerial volcanoes (open yellow triangles). Note
Niuafo’ou volcano and island, and the location of Lobster (and Dugong, a neighboring volcano
discussed in a separate Bulletin report and plotted on a larger map). Abbreviations are as
follows: VFR - Valu fa ridge; ELSC - East Lau spreading center; ILSC - Intermediate Lau
spreading center; CLSC - Central Lau spreading center; LETZ - Lau Extentional transform zone;
PR - Peggy Ridge; NWLSC - Northwest Lau spreading center; NSC - Niuafo'ou spreading center
(location of Rochambeau Rifts); NELSC - Northeast Lau spreading center; FSC - Fonualei
spreading center; and MTJ - Mangatolu triple junction. Courtesy of Keller and others (2008).
Lobster volcano’s caldera is 2x2.5 km in diameter with a floor at 1.5 km depth (figure 2).
It was described as residing amid four radiating rift zones.
Figure 2. (a) Multibeam sonar three-dimensional (30 kHz swathmap) image made in 2008 of
Lobster which sits in what was described as the center of a rift zone and astride a spreading ridge
to its W (CSIRO, 2008). Image lacks scale for depth values, but in relative terms light blue is the
deepest, trending upwards through dark-to-light green, yellow, orange, and then red as the
shallowest. Image from news release of CSIRO (2008b). (b) Shaded relief, contour map of
Lobster caldera on the Rochambeau rifts showing part of a survey track completed in 2010 by
the research vessel Dorado Discovery. Taken from Lupton and others (2012). (c) Detail map of
Lobster Caldera showing locations and profiles for two chemistry hydrocasts. Inserts show
vertical profiles of 3He (deviation of the 3He/4He ratio measured at depth from the atmospheric
ratio), total Mn (manganese), and %T transmission of light (a measure of suspended particles)
plotted versus depth. Taken from Lupton and others (2012).
The caldera’s rim is about 100 m high on the W side whereas only ~20 m high on the E
side.
Dredge samples from Lobster recovered in 2008 contained olivine and plagioclase in
pillow basalts. A dredge sample taken on the smooth caldera floor recovered fresh flows as well
as thick, black aphyric pillows with glassy rinds.
Age. According to Arculus (2008) and Lupton and others (2012), active venting was
identified in the form of high helium anomalies (3He), suspended particles (%T), and trace
metals (manganese and iron) at 60 m off the bottom in the SE corner of the summit caldera.
Lupton and others (2012) reported, in 2012, that the site was still active.
The expedition mapped the seafloor using a 30 kHz multibeam sonar with Global
Positioning System (GPS) and an Inertial Motion Unit (IMU) to track the ship’s position and
attitude. They also made vertical conductivity, temperature, and depth (CTD) measurements as
well as rock dredging. In addition, by lowering the CTD package up and down a few hundred
meters from the bottom, while moving the ship, they obtained a far greater density of data. This
technique, often informally referred to as a CTD tow-yo, is effective for mapping and sampling
hydrothermal plumes.
References: Arculus, R.J., 2008, Marine National Facility RV Southern Survey 2008
Program: Voyage Summary SS07/2008 Northern Lau Vents Expedition (NoLauVE), 23 p (URL:
http://www.cmar.csiro.au/datacentre/process/data_files/cruise_docs/SS200807sum.pdf).
CSIRO, 2008a, Active submarine volcanoes found near Fiji, CSIRO web site (URL:
http://www.csiro.au/Organisation-Structure/Divisions/Earth-Science--ResourceEngineering/SubmarineVolcanoes.aspx).
CSIRO, 2008b, Active submarine volcanoes found near Fiji, CSIRO media release (URL:
http://www.scienceimage.csiro.au/mediarelease/mr08-93.html).
de Ronde, C.E.J, Baker, ET, Massoth, G.J, Lupton, J.E, Wright, I.C., Feely, R.A., and
Greene, R.R., 2001, Intra-oceanic subduction-related hydrothermal venting, Kermadec volcanic
arc, New Zealand, Earth and Planetary Science Letters, v. 193, p. 359-369.
Graham, I.J., Reyes, A.G., Wright, I.C., Peckett, K.M., Smith, I.E.M., and Arculus, R.J.,
2008, Structure and petrology of newly discovered volcanic centers in the northern Kermadec–
southern Tofua arc, South Pacific Ocean, Journal of Geophysical Research, v. 113, B08S02,
doi:10.1029/2007JB005453.
InterRidge Vents Database Ver. 3.1, 2013, Vent Fields (URL:
http://www.interridge.org/irvents/ventsfields?).
Keller, N.S., Arculus, R.J., Hermann, J., and Simon, R., 2008, Submarine back-arc lava
with arc signature: Fonualei Spreading Center, northeast Lau Basin, Tonga, Journal of
Geophysical Research, v. 113, B08S07, doi:10.1029/2007JB005451.
Lupton, J.E., Arculus, R.J., Resing, J., Massoth, G.J., Greene, R.R., Evans, L.J., and
Buck, N., 2012, Hydrothermal activity in the Northwest Lau Backarc Basin: Evidence from
water column measurements, Geochemistry, Geophysics, Geosystems, v. 13, no. 5, doi:
10.1029/2011GC003891.
Information Contacts. Commonwealth Scientific and Industrial Research Organization
(CSIRO) (URL: http://www.csiro.au).