Exploring the Kermadec volcanic arc

Short-term temporal changes in the characteristics of hydrothermal plumes at Rumble III volcano on the Kermadec arc, New Zealand

The Kermadec arc, off the north east coast of New Zealand, hosts numerous submarine volcanoes. Many of these volcanoes are located at shallow depths, are highly active and are associated with hydrothermal plumes. Plumes rise buoyantly through the water column and “settle out” at a depth based on their density. The distribution of black smoker plumes can be mapped using a light scattering sensor to detect anomalously high particle concentrations. Variability in vent source conditions and the water column, in particular background currents, result in changes in plume distribution on short temporal scales. Therefore, it is difficult to obtain an accurate picture of plume dynamics based on a single “snapshot”. Rumble III volcano on the Kermadec arc has a shallow summit (310 m), and rising hydrothermal plumes are strongly influenced by surface currents that vary over the tidal cycle. The unique shallow depth of Rumble III was utilized in this study to more easily and accurately investigate changes in plume distribution over the tidal cycle. Surveying occurred in March 2009, aboard the R/V Thomas G. Thompson as part of a student field course in collaboration with New Zealand scientists, Dr. Cornel de Ronde and Sharon Walker. Measurements with a conductivity-temperature-depth-optical (CTD-O) package revealed some of the highest particle anomaly signals ever recorded in a hydrothermal plume and were correlated with strong temperature anomalies. Background currents were quantified at Rumble III based on acoustic doppler current profiler (ADCP) analyses and used together with plume rise heights and temperature anomalies to document plume variability. The intensity, location and structure of plumes varied with the tides, highlighting the inaccuracy of characterizing a hydrothermal system based on one survey. Results have been used in concert with simple buoyant plume models to estimate previously unknown vent source conditions at Rumble III. The calculated heat flux (107 &plusmn7 MW) is over an order of magnitude greater than previous estimates, emphasizing the need to monitor hydrothermal vents to accurately estimate their contribution to the oceans heat budget.