Volcanoes In The Ocean

Oceanic volcanoes develop mainly by movements in Earth’s crust, segmented in large pieces, or tectonic plates. The tectonic plates continue to move, and their movements cause volcanic activity in three basic ways:

1. Mid-Ocean Ridges: The Earth’s most extensive volcanic activity is on mid-ocean ridges, where tectonic plates are moving apart. As they do, mantle magma moves up to take up space, solidifying and becoming new crust for the seafloor. The slow spreading on the seafloor widens the ocean basins. The Mid-Atlantic Ridge is a perfect example of such activity.
2. Subduction Zones: In places, a tectonic plate is driven under another in a process called subduction. As the lower plate is driven downwards towards Earth’s warmer regions of the mantle, it melts and forms magma, and ultimately, makes it to Earth’s surface to form volcanoes. The world’s deepest point, the Mariana Trench, is in a subduction zone and is dotted with multiple active volcanoes underwater.
3. Hotspots: Some volcanoes form in the middle of tectonic plates, where there is no ridge and no subduction. These volcanoes form through mantle plumes—columns of heated-up rock rising up from deep in Earth. As a tectonic plate moves over a stationary hotspot, a chain of volcanoes may form. The Hawaiian Islands formed in such a way, and new islands formed progressively while the plate moved.

Because they’re surrounded by water, undersea eruptions have distinct behavior compared to on-land eruptions. Water changes how magma cools, how gas is able to exit, and how explosive an eruption is. There are three basic types of undersea eruptions:

1. Effusive Eruptions: These eruptions result in lava in a smooth flow rather than an explosion. The lava quickly solidifies on hitting the water, and forms characteristic, spherical structures, or pillow basalts. These eruptions tend to pile up on top of the floor of the ocean in time, and contribute to seafloor spreading.
2. Explosive Eruptions: If there is sufficient gas in the magma, pressure might build up and lead to violent explosive activity. The gas and heat, quickly released, result in explosive materials and volcanic ash, and in extreme cases, might rise to the surface of the ocean or even create temporary islands. There have been explosive eruptions by shoreland undersea volcanoes.
3. Hydrothermal Venting: Submarines have multiple hydrothermal vents, through which seawater seeps through the bottom of the ocean, is heated by magma, and spews up in the ocean, releasing dissolved minerals. The black and white smokers, so named for their appearance, provide special communities living on chemical, instead of sunlight, energies.

Underwater volcanoes have two types of effects on marine life: good and bad.

• Creating New Habitats: As lava solidifies, it presents a new surface for marine life to colonize. Coral, sponges, and marine life in general tend to take up residence on rock, establishing diverse and fertile marine communities.
• Nutrient Supply: Volcanism is responsible for delivering necessary nutrients including sulfur and iron, giving nutrients to life in deep waters. Bacteria in and around hydrothermal vents metabolize such compounds for their source of power, and such bacteria in turn provide food to tube worms, giant clams, and specialized animals through food webs.
• Destructive Effects: On the other hand, explosive eruptions have catastrophic effects, including degrading marine life, releasing noxious fumes, and altering water chemistry. Large amounts of ash and fragments emanating from some eruptions have the power to suffocate marine life and destabilize local communities.

Oceanic volcanoes influence not only the ocean but also the atmosphere and climate. Among their major effects are:

1. Gas Emissions: Volcanoes also produce carbon dioxide (CO2) and sulfur dioxide (SO2) gas. CO2 is implicated in global warming, while SO2 creates short-run cooling by releasing minute particles in the atmosphere, reflecting sunlight.
2. Ocean Acidification: The CO2 in seafloor eruptions dissolves in seawater and forms carbonic acid, lowering the pH of the ocean. This makes marine animals, including corals and shellfish, have a harder time building their protective skeletons and shells.
3. Tsunamis and Earthquake Activity: The ability to cause undersea earthquakes and hence, tsunamis, is found in large eruptions. These massive waves have the capability to inundate entire ocean basins and destroy coastal regions.

1. Loihi Seamount (Hawaii): Loihi is a slowly growing undersea volcano, located off the coast of the Big Island. In time, it is expected to rise to sea level to form a new Hawaiian island.
2. Kick ’em Jenny (Caribbean): This highly active submarine volcano near Grenada has erupted multiple times and poses a potential tsunami risk.
3. Axial Seamount (Pacific Ocean): An Oregon coastal volcano under intensive surveillance, Axial Seamount is no stranger to recent activity and is providing top-notch data for scientists.

Since underwater volcanoes are inaccessible, scientists have to use advanced technologies to study them. Among their chief tools are:

• Remotely Operated Vehicles (ROVs): These unmanned submarines descend to deep-sea volcanoes, capture photos, and retrieve samples.
• Seismic Monitoring: Networked seismometers beneath the water surface detect vibrations caused by earthquake and volcano activity.
• Satellite Imaging: Satellites help in observing large-scale eruptions by gauging gas emissions and alterations in seawater temperature.
• Acoustic Sensors: Hydrophones, specialized microphones designed for use underwater, capture sounds of eruptions in real time.

Scientists continue to explore how undersea volcanoes influence Earth’s environment. As monitoring equipment is developed, scientists anticipate having enhanced forecasts for eruptions and their eventual influence on marine life and world climate. Further discovery excursions may also identify unknown undersea volcanoes, showing us more of such hidden natural power.

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