Brothers is an active submarine caldera volcano in the Kermadec Arc, 400 km north east of White Island. It is an oval shape about 13 km long and 8 km wide. The 3 km wide summit caldera has very steep walls 300-500 metres high. The caldera floor is 1850m below sea level, and has a 350 metre high dome within it.
For a one page fact sheet / poster on Brothers Volcano click VolcanoFactSheets Brothers.pdf (548.34 kB)
At present Brothers has more hydrothermal activity than any other volcano in the Kermadec Arc. Hydrothermal vents (hot springs) on the caldera wall and the dome have formed a large field of “black smoker’ chimneys up to 8m high. Plumes of hot water from the vents can rise 750 metres through the ocean above.
When hot hydrothermal fluid jets out of a vent, it mixes with cold sea water and metals in the fluid precipitate out of the solution. The plumes of black ‘smoke’ created by this reaction settle and form deposits of metallic minerals on the crater floor. As this reaction occurs it can also build ‘chimneys’ rich in metals above the vents.
The area around the hydrothermal vents has unique forms of marine life such as tubeworms, and bacteria which use the hydrothermal fluids as an energy source.
The eruptive history, including that of any recent eruptions is still unknown. The crater walls reveal layers of dacite lava flows from which a later eruption has blown out a caldera.
Undersea volcanoes are not monitored by GNS Science, however they are a focus of current exploration. The spectacular minerals and marine life found around active undersea volcanoes may have economic and biotechnology benefits for New Zealand.