The Brothers Seamount (also Brothers Volcano) is a Pacific Ocean

submarine volcano Submarine volcanoes are underwater vents or fissures in the Earth's surface from which magma can erupt. Many submarine volcanoes are located near areas of tectonic plate formation, known as mid-ocean ridges. The volcanoes at mid-ocean ridges ...

in the Kermadec Arc, north east of New Zealand's

Whakaari/White Island Whakaari / White Island (, mi, Te Puia Whakaari, lit. "the dramatic volcano"), also known as White Island or Whakaari, is an active andesite stratovolcano situated from the east coast of the North Island of New Zealand, in the Bay of Plent ...

. It is one of the

South Kermadec Ridge Seamounts The South Kermadec Ridge Seamounts are a continuation of the volcanic island arc, formed at the convergent boundary where the Pacific Plate subducts under the Indo-Australian Plate. The subducting Pacific Plate created the Kermadec Trench, the s ...

Geology

It was formed by volcanic activity within a

graben In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic contex ...

structure delimited by regional faults created by

subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

of the

Pacific Plate The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At , it is the largest tectonic plate. The plate first came into existence 190 million years ago, at the triple junction between the Farallon, Phoenix, and Iza ...

under the Australian Plate. Within its oval outline, which measures , it contains a wide

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...

with walls high. It is three times bigger than

Whakaari / White Island Whakaari / White Island (, mi, Te Puia Whakaari, lit. "the dramatic volcano"), also known as White Island or Whakaari, is an active andesite stratovolcano situated from the east coast of the North Island of New Zealand, in the Bay of Plent ...

. A dacite dome named the Upper Cone rises 350 m from the caldera floor (which lies 1850 m below sea level), with a smaller dome just to its northeast. There is now detailed magnetic anomaly mapping of the Brothers caldera with very extreme range variation from −2000 to +2000 nT. 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.

Hydrothermal activity

The caldera walls and the larger dome host numerous

hydrothermal vent A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspot ...

s, 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. These hydrothermal vents are also known as

hot springs A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by circ ...

and have created an 8 meter high field of " black smoker" chimneys. These chimneys are created when the hydrothermal fluids hit the cold water and the chemicals in solution are deposited. The hydrothermal fluids are an energy source to many unique species of organisms like

tubeworms A tubeworm is any worm-like sessile invertebrate that anchors its tail to an underwater surface and secretes around its body a mineral tube, into which it can withdraw its entire body. Tubeworms are found among the following taxa: * Annelida, the ...

and bacteria. The marine life and minerals found from these chimneys are beneficial to New Zealand's economy and biotechnology industry. It is likely that the richest mineral deposits should be in the caldera rim and walls. Two main types of hydrothermal activity exist: # In the Upper Caldera and NW-Caldera high temperature hydrothermal vents exist with medium gas enrichment and the formation of Cu-Zn-Au-rich chimneys # At the Upper and Lower Cones lower temperature (< 120 °C) diffuse venting of very gaseous acidic sulfate containing fluids

History

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 a

. Drill samples of hydrothermally altered volcanoclastics products and lava flows of dacitic composition show a two stage history: # Pre-caldera collapse with magmatic activity, including a dominant magmatic-hydrothermal system of acid sulfhate fluids, magmatic volatiles and metal rich brines, followed by # Post-caldera collapse with the growth of the resurgent Upper and Lower Cones, and new magmatic hydrothermal activity. This sequence was established by a joint expedition by the United States, New Zealand and Germany that mapped the volcano in detail in 2007, and cores of the volcano and its hydrothermal systems that were taken during IODP Expedition 376 (D/V JOIDES Resolution, May–July 2018).

Monitoring

Submarine volcanoes are not monitored by any organization, but have become a central interest in current expeditions.

References

External links