| Brothers Seamount | |
|---|---|
 Brothers Volcano as looking into the caldera from the south | |
 Location of Brothers Seamount | |
| Summit depth | 1,350 m (4,430 ft) |
| Location | |
| Coordinates | 34°52′30″S179°04′30″E / 34.875°S 179.075°E /-34.875; 179.075 |
| Geology | |
| Type | Submarine volcano |
| Last eruption | Unknown |
TheBrothers Seamount (alsoBrothers Volcano) is a Pacific Oceansubmarine volcano in theKermadec Arc, 340 kilometres (210 mi) north east of New Zealand'sWhakaari/White Island. It is one of theSouth Kermadec Ridge Seamounts.
It was formed by volcanic activity within agraben structure delimited by regional faults created bysubduction of thePacific Plate under theAustralian Plate.[1][2]Within its oval outline, which measures 13 by 8 kilometres (8.1 by 5.0 mi), it contains a 3 km (1.9 mi) widecaldera with walls 300–500 metres (980–1,640 ft) high. It is three times bigger thanWhakaari / White Island.[2] Adacite[2] dome named the Upper Cone[1] rises 350 m from the caldera floor (which lies 1850 m below sea level), with a smaller dome just to its northeast.[3] There is now detailedmagnetic anomaly mapping of the Brothers caldera with very extreme range variation from −2000 to +2000 nT.[1] Such mapping has shown that the local magnetic highs correlate with the morphology of the caldera, in particular its rim and the Upper Cone, whereas magnetic lows correlate with zones of hydrothermal activity and/or alteration of the rocks by the hydrothermal fluids.[1]
The caldera walls and the larger dome host numeroushydrothermal vents, which send plumes of hot water 750 m up through the water column. It is the most hydrothermally active volcano known in the Kermadec Arc.[3][1] These hydrothermal vents are also known ashot springs and have created an 8 meter high field of "black smoker" chimneys.[4] These chimneys are created when the hydrothermal fluids hit the cold water and the chemicals in solution are deposited.[2] The hydrothermal fluids are an energy source to many unique species of organisms liketubeworms and bacteria.[4] The marine life and minerals found from these chimneys are beneficial to New Zealand's economy andbiotechnology industry.[2] It is likely that the richest mineral deposits should be in the caldera rim and walls.[1]
Two main types of hydrothermal activity exist:[1]
It is still unknown when the Brothers Volcano last erupted, but the crater walls tell us that it had an eruption sequence that was so explosive that it caused the volcano to blow out acaldera.[4] Drill samples of hydrothermally altered volcanoclastics products and lava flows of dacitic composition show a two stage history:[1]
This sequence was established by a joint expedition by the United States, New Zealand and Germany that mapped the volcano in detail in 2007,[5] and cores of the volcano and its hydrothermal systems that were taken during IODP Expedition 376 (D/V JOIDES Resolution, May–July 2018).[1]
Submarine volcanoes are not monitored by any organization, but have become a central interest in current expeditions.[2]
