This global view of the Pacific Ocean basin shows the Ring of Fire and the location of Explorer Ridge and the Marianas volcanic arc. Click image for larger view and more details
Submarine Volcanism 2004
Bill Chadwick
Oregon State University
NOAA Vents Program
The "Ring of Fire" is a circular arc of active volcanoes that surrounds the Pacific Ocean basin. Much is known about the volcanoes on land within the Ring of Fire (for example, in the Aleutians, the Cascades, the Andes, etc.), but comparatively little is known about the submarine volcanoes, simply because they are more difficult to observe. This multi-year project aims to explore submarine volcanoes within the Ring of Fire in two very different tectonic settings on either side of the Pacific: one in which new sea floor is created and the other in which old sea floor is destroyed.
Volcanoes and Plate Tectonics
The Earth is covered with tectonic plates that are in constant motion over the partially molten interior. Almost all the volcanoes and earthquakes on Earth occur where tectonic plates are either moving apart or are coming together.
Most submarine volcanoes and earthquakes occur where tectonic plates are either colliding or moving apart. Click image for larger view
Where tectonic plates are moving apart, molten rock (magma) rises up from deep within the Earth to fill the gap and create new ocean floor. The boundaries between separating plates are called "spreading centers" or "mid-ocean ridges," and they are the sites of frequent submarine volcanic eruptions.
View the 3-dimensional structure of a mid-ocean ridge. (QuickTime, 576Kb) A Quicktime VR animation of the ridge is also available (2.6Mb)
Explorer Ridge in the northeast Pacific is an example of a mid-ocean ridge and was the focus of our exploration program during the 2002 Submarine Ring of Fire expedition.
Watch an animation that shows the deployment of ABE, and the different sonar surveys that were used to characterize the Magic Mountain site. (Quicktime, 2.1 Mb).
Where tectonic plates are moving toward each other or colliding, one plate is usually forced under the other in a process called subduction. At subduction zones, the plate that is forced downward dives back into the Earth and is eventually melted and recycled. This process also causes melting above the subduction zone. This molten rock rises back up to the surface to feed chains of active volcanoes called volcanic arcs. Volcanic arcs can be on land or underwater, or can be a combination of islands and submarine volcanoes. The Marianas Arc in the Western Pacific is an example of a volcanic arc with many volcanic islands and underwater volcanoes, and is the focus of this year's Submarine Ring of Fire expedition, as it was in 2003.
View the 3-dimensional structure of a subduction zone. (QuickTime, 824Kb) A Quicktime VR animation of the subduction zone is also available (1.8Mb)
Submarine eruptions at mid-ocean ridges produce fresh lava flows like these "pillow" lavas, which form as lava slowly oozes out of a fissure on the sea floor. Click image for larger view and more details
Satellite derived bathymetry from Sandwell and Smith (1997) of the Mariana Arc region. 500-m contour interval. Islands are labeled in black. Small white stars indicate submarine volcanoes. Click image for larger view and more details
Volcanoes in these two different settings have very different characteristics. Mid-ocean ridge volcanoes tend to be linear, and look like long, low ridges, whereas arc volcanoes are cone shaped, centralized, and isolated. Mid-ocean ridge volcanoes also have more primitive lava compositions because the lava comes more or less directly from the Earth's interior without changing much. On the other hand, the lava that reaches arc volcanoes rises through a longer path from its source region to the surface, so its composition can change significantly along the way. This difference is reflected in the fact that mid-ocean ridge eruptions are generally nonexplosive, whereas arc eruptions are often explosive.
Volcanoes, Hydrothermal Vents, and Life
Where submarine volcanoes bring hot magma near the sea floor or cause lava to erupt at the surface, sea-floor hot springs called hydrothermal vents are common. Seawater that circulates deep within a submarine volcano gets heated up before it returns to the sea floor. Hydrothermal vent fluid is rich in dissolved chemicals, and these “black smokers” support a unique ecosystem of microorganisms and animals that is not dependent on sunlight.
The Magic Mountain Virtual Site Take a trip to the sea floor! Explore the hydrothermal vents of the Magic Mountain Vent Fields with virtual fly-through movies, panoramas, and video clips.
Biotech companies are particularly interested in the heat-tolerant microbes that live on and below the sea floor at submarine volcanoes because they have novel enzymes that may be useful for creating new medicines. Because the DNA of organisms living at sea-floor hot springs is very primitive, some scientist believe that life on Earth may have originated at deep-sea hydrothermal vents on submarine volcanoes.
