Volcanism at mid-ocean ridges

Classic example of a pit and pillar feature from Endeavour Ridge.

The great majority of the Earth’s volcanism occurs at spreading centers, most of which are under the ocean, forming the mid-ocean ridge system where new ocean crust is being created. The Earth’s tectonic plates are slowly moving apart, and magma rises up to fill the gap, adding to the deep crust as sheeted dikes and sometimes flowing onto the seafloor as volcanic eruptions. The shallow magma provides a heat source that causes intense circulation of water within the shallow oceanic crust and the venting of the heated, mineral-laden water at the seafloor. These hot springs and spectacular hydrothermal vents transport heat and chemicals into the ocean and provide substrate for chemosynthetic biological communities.

The Gorda, Juan de Fuca and Endeavour Ridges have slow (~25 mm/yr) to moderate spreading rates, and are located off Oregon and Washington states and British Columbia. The Northern East Pacific Rise has a fast spreading rate, and is located off Mexico, south of the Gulf of California. Segments of the Southern East Pacific Rise have super-fast spreading rates (>140 mm/yr), the fastest of which are south-west of Easter Island in the South Pacific.

A major focus of our work has been at Axial Seamount, which is a hot spot interacting with the Juan de Fuca Ridge and where eruptions occurred in 1998 and 2011. We have mapped with our AUV at high resolution the summit caldera, upper flanks, and a large portion of the south rift zone, and extensively sampled with the ROVs lavas and sediments to obtain a record of the eruptive and explosive history of the volcano. Our papers on Axial Seamount are profiled in this Mid-ocean ridge section’s Volcanic Processes, Magmatic Processes, and Explosive Eruptions pages, and in our recent cruise logs.

Note that off-axis, near-ridge seamounts are discussed in the Seamounts section of this web.


Back arc spreading ridges

Behind the trench and volcanic arc of a subduction zone, the lithosphere may stretch and extend and volcanic spreading centers may develop. Such a back arc setting is found in the Lau Basin, behind the Tonga Trench in the South Pacific.

Hydrothermal systems

Hydrothermal vents are important for many reasons, including global fluxes of elements, deposits of economically-valuable minerals, and diverse assemblages of previously unknown animals and bacteria that are supported by the chemically-rich waters emanating from the vents.

Explosive eruptions

The volcanic eruptions at mid-ocean ridges have been thought only to be quietly effusive, but because we find glassy fragments of lava bubbles (limu o Pele) at mid-ocean ridges, there must be gas-rich mildly explosive eruptions at mid-ocean ridges as well.

Mid-ocean ridge volcanic processes

MBARI mapped the 2011 eruption at Axial Volcano with our AUV. Surprises included how most of the fissures had been pre-existing, and were reused (even widened and deepened) and fed lava into pre-existing channels.

Magmatic processes

AUV maps allow us for the first time, to comprehensively map the thickness and extent of lava flows from a deep-ocean submarine eruption in high resolution.


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