Why Are Scientists Exploring the Submarine Ring of Fire?
A key purpose of NOAA’s Ocean Exploration Initiative is to investigate the more than 95 percent of Earth’s underwater world that until now has remained virtually unknown and unseen. Such exploration may reveal clues to the origin of life on Earth, cures for human diseases, answers on how to achieve sustainable use of resources, links to our maritime history, and information to help protect endangered species. In addition, exploration of active volcanoes provides important information on potential hazards such as risks to shipping from shallow eruptions, as well as the generation of dangerous tsunamis from large submarine eruptions and landslides.
The Submarine Ring of Fire is an arc of active volcanoes that partially encircles the Pacific Ocean Basin, including the Kermadec and Mariana Islands in the western Pacific, the Aleutian Islands between the Pacific and Bering Sea, the Cascade Mountains in western North America, and numerous volcanoes on the western coasts of Central America and South America. These volcanoes result from the motion of large pieces of the Earth’s crust known as tectonic plates. This volcanic activity releases immense quantities of heat, minerals, gases and other substances, and often produces “hydrothermal systems” or seafloor hot springs. These processes influence the entire ocean, and support unique biological communities. Many species in these communities are new to science, and have a high potential for developing important new natural products for industrial and medical applications. In addition, fluids produced by volcanic activity often have high concentrations of metals that quickly precipitate in cold ocean waters, and may be directly linked to the formation of ores and concentrated deposits of gold and other precious and exotic metals.
Beginning in 2002, Ocean Exploration expeditions have undertaken systematic mapping and study of hydrothermal systems in previously unexplored areas of the Submarine Ring of Fire. The first of these expeditions (http://oceanexplorer.noaa.gov/explorations/02fire/) focused on Explorer Ridge, part of the seafloor spreading center about 160 km south of Vancouver Island, Canada. This expedition produced the first highly detailed maps of a major hydrothermal field known as “Magic Mountain,” and located more than 30 active vents (see http://oceanexplorer.noaa.gov/explorations/02fire/logs/magicmountain/).
In 2003 and 2004, the Submarine Ring of Fire Expeditions (http://www.oceanexplorer.noaa.gov/explorations/03fire/ and http://www.oceanexplorer.noaa.gov/explorations/04fire/) explored the submarine volcanoes of the Mariana Arc, located to the north of Guam in the western Pacific. These volcanoes are the result of converging tectonic plates, in contrast to the diverging plates at Explorer Ridge. These expeditions discovered at least ten new hydrothermal sites, and were on site during an actual eruption of a volcano that spewed hot acidic fluid, molten sulfur, and chunks of volcanic ash (see http://oceanexplorer.noaa.gov/explorations/04fire/logs/april01/april01.html). The expeditions also deployed Autonomous Underwater Hydrophones to monitor undersea seismicity and marine mammal activity. See http://www.oceanexplorer.noaa.gov/explorations/03fire/logs/feb22/feb22.html for more about these instruments and the ocean’s SOFAR region that “traps” sound and allows it to be heard at extremely long distances.
The 2005 Submarine Ring of Fire Expedition (http://www.oceanexplorer.noaa.gov/explorations/05fire/) explored the volcanoes of the Kermadec Arc, located north of New Zealand. Manned submersibles were used to explore active hydrothermal systems that had never been visited before. Some of these systems were well within the photic zone at 160-180 meters, so that chemosynthetic systems overlapped with organisms from photosynthetic systems. Iron-rich fluids venting at one volcano were accompanied by large areas (acre size) covered with actively-forming or recently-formed microbial mats.
In 2006, the Submarine Ring of Fire Expedition (http://oceanexplorer.noaa.gov/explorations/06fire/welcome.html) continued exploration of submarine volcanoes along the Marina Arc. Discoveries included an actively erupting volcano, liquid carbon dioxide vents, the shallowest “black smoker” yet discovered, and more than 12 new species of chemosynthetic organisms at hydrothermal vent sites.
In 2007, the New Zealand American Submarine Ring of Fire Expedition focuses on detailed exploration of hydrothermal systems at Brothers Volcano. Previous expeditions have mapped this area at a resolution of about 35 meters (so features smaller than 35 meters are “invisible”). This resolution gives a good impression of the overall shape of the area, but cannot reveal details about the location and features of hydrothermal communities. The 2007 expedition will produce maps with a resolution of about one meter, which will provide much more detailed information about the most hydrothermally-active submarine volcano on the Kermadec Arc. Key goals include:
- Complete a high-resolution bathymetric, magnetic, and chemical survey of Brothers Caldera (a caldera is a large depression at the top of a volcano, and is more fully-described below) using the Autonomous Benthic Explorer (ABE) underwater robot (see “Expedition Technology”);
- If time permits, survey the summit of a second Kermadec Arc volcano; and
- Collect CTD/rosette data (see “Expedition Technology”) to groundtruth CTD data collected by ABE.
More About Plate Tectonics and the Submarine Ring of Fire
Tectonic plates are portions of the Earth’s outer crust (the lithosphere) about 5 km thick, as well as the upper 60 - 75 km of the underlying mantle. The plates move on a hot flowing mantle layer called the asthenosphere, which is several hundred kilometers thick. Heat within the asthenosphere creates convection currents (similar to the currents that can be seen if food coloring is added to a heated container of water). These convection currents cause the tectonic plates to move several centimeters per year relative to each other.
The junction of two tectonic plates is called a “plate boundary.” Three major types of plate boundaries are produced by tectonic plate movements. If two tectonic plates collide more or less head-on they form a convergent plate boundary. Usually, one of the converging plates will move beneath the other, which is known as subduction. Deep trenches are often formed where tectonic plates are being subducted, and earthquakes are common. As the sinking plate moves deeper into the mantle, fluids are released from the rock causing the overlying mantle to partially melt. The new magma (molten rock) rises and may erupt violently to form volcanoes, often forming arcs of islands along the convergent boundary. These island arcs are always landward of the neighboring trenches. For a 3-dimensional view of a subduction zone, visit: http://oceanexplorer.noaa.gov/explorations/03fire/logs/subduction.html.
The junction of two tectonic plates that are moving apart is called a divergent plate boundary. Magma rises from deep within the Earth and erupts to form new crust on the lithosphere. Most divergent plate boundaries are underwater (Iceland is an exception), and form submarine mountain ranges called oceanic spreading ridges. While the process is volcanic, volcanoes and earthquakes along oceanic spreading ridges are not as violent as they are at convergent plate boundaries. View the 3-dimensional structure of a mid-ocean ridge at: http://oceanexplorer.noaa.gov/explorations/03fire/logs/ridge.html.
The third type of plate boundary occurs where tectonic plates slide horizontally past each other, and is known as a transform plate boundary. As the plates rub against each other, huge stresses are set up that can cause portions of the rock to break, resulting in earthquakes. Places where these breaks occur are called faults. A well-known example of a transform plate boundary is the San Andreas fault in California. See animations of different types of plate boundaries at:
The volcanoes of the Submarine Ring of Fire result from the motion of several major tectonic plates. The Pacific Ocean Basin lies on top of the Pacific Plate. To the east, along the East Pacific Rise, new crust is formed at the oceanic spreading center between the Pacific Plate and the western side of the Nazca Plate. Farther to the east, the eastern side of the Nazca Plate is being subducted beneath the South American Plate, giving rise to active volcanoes in the Andes. Similarly, convergence of the Cocos and Caribbean Plates produces active volcanoes on the western coast of Central America, and convergence of the North American and Juan de Fuca Plates causes the volcanoes of the Cascades in the Pacific Northwest.
On the western side of the Pacific Ocean, the Pacific Plate converges against the Philippine Plate and Australian Plate. Subduction of the Pacific Plate creates the Marianas Trench (which includes the Challenger Deep, the deepest known area of the Earth’s oceans) and Kermadec Trench. As the sinking plate moves deeper into the mantle, new magma is formed as described above, and erupts along the convergent boundary to form volcanoes. The Mariana and Kermadec Islands are the result of this volcanic activity, which frequently causes earthquakes as well. The movement of the Pacific Ocean tectonic plate has been likened to a huge conveyor belt on which new crust is formed at the oceanic spreading ridges, and older crust is recycled to the lower mantle at the convergent plate boundaries of the western Pacific. For more information on plate tectonics, visit the NOAA Ocean Explorer Multimedia Discovery Missions. Click on the links to Lessons 1, 2 and 4 for interactive multimedia presentations and Learning Activities on Plate Tectonics, Mid-Ocean Ridges, and Subduction Zones.
More About Volcanism and Hydrothermal Vents Along the Kermadec Arc
Volcanoes at convergent plate boundaries along the Kermadec and Mariana arcs often erupt as violent explosions, and form chains of isolated cone-shaped islands. In contrast, volcanoes found near the divergent plate boundaries of oceanic spreading ridges generally do not erupt explosively and look like long, low ridges. Many volcanoes in the
Kermadec and Mariana arcs form calderas, which are large depressions at the top of a volcano. A caldera is formed when so much magma erupts from a volcano that an empty chamber is left beneath the volcano, and the overlying surface collapses into the chamber. See the satellite and sonar survey animation of the Mariana Arc Volcanic Chain at:
When seawater penetrates the permeable ocean crust in the vicinity of volcanoes, increased heat and pressure cause a variety of gases, metals and other materials to dissolve into the water from the surrounding rock. This process causes many metals to be concentrated by a thousand to a million times their concentration in normal seawater. When the fluid is vented into cold ocean water, some dissolved substances precipitate out of solution, forming metal deposits, “chimneys,” and “black smokers.” Dissolved gases may react to form other materials. At NW Rota Volcano, for example, dissolved sulfur dioxide forms sulfuric acid and elemental sulfur. At NW Eifuku Volcano, 1600 meters below the sea surface, the 2004 Ring of Fire Expedition found buoyant droplets of liquid carbon dioxide, probably formed from degassing of a carbon-rich magma.
Hydrothermal fluids also provide an energy source for a variety of chemosynthetic microbes that in turn are the basis for unique food webs associated with hydrothermal vents. Many of these microbes have specific adaptations to extreme conditions; scientists found evidence for microbes living in hot spring fluids on NW Rota with a pH of 2.0 or less. Other new and unique microbes are expected to be found in association with extreme vent fluids as other sites are identified and explored along the Kermadec Arc.
The key technology component of the New Zealand American Submarine Ring of Fire 2007 Expedition is the Autonomous Benthic Explorer (ABE), a one-of-a-kind underwater robot that operates independently without a pilot or cable connected to a ship or submersible. This independence allows ABE to cover large areas of the ocean floor, as well as to monitor a specific underwater area over a long period of time. ABE can follow the contours of underwater mountain ranges, fly around sheer pinnacles, dive into narrow trenches, take photographs, and collect data and samples at a top cruising speed of 2 knots.
ABE is a little over 2 meters long, weighs about 1,200 pounds, and can survey bottom environments at depths of 5000 meters. Onboard equipment includes conductivity and temperature probes, a depth recorder, video cameras, a magnetometer, sonar for advanced mapping, geological sampling tools, and a wax core sampler that collects rock and sediment samples by pressing a heavy weight with sticky wax on its bottom onto the seafloor. ABE was designed and built at the Woods Hole Oceanographic Institution (WHOI) in the mid 1990’s. For more information, visit http://dsg.whoi.edu:90/ships/auvs/abe_description.htm.
In addition to ABE, a variety of other devices will be used to explore the volcanoes and hydrothermal vent systems of the Kermadec Arc. An instrument called a CTD will be used to collect data on seawater conductivity, temperature, and depth. These data can be used to determine salinity of the seawater which is a key indicator of different water masses. In addition to the CTD carried by ABE, a second CTD attached to a water sampling array known as a rosette will be deployed from the research ship to verify results from the robotic survey. For more information on CTDs and rosettes visit http://oceanexplorer.noaa.gov/technology/tools/sonde_ctd/sondectd.html.
Detailed bathymetric maps and three-dimensional images of the Brother Caldera will be made with a multibeam sonar system. Multibeam sonars send out multiple, simultaneous sonar beams in a fan-shaped pattern that is perpendicular to the ship’s track. This allows the seafloor on either side of the ship to be mapped at the same time as well as the area directly below (visit http://oceanexplorer.noaa.gov/technology/tools/sonar/sonar.html for more information).
For More Information
Contact Paula Keener-Chavis, national education coordinator for the NOAA Office of Ocean Exploration, for more information.
Other lesson plans developed for this Web site are available in the Education Section.