Seamounts of the Mariana Arc

The Mariana volcanic arc is a chain of underwater volcanoes (seamounts).  In this 3D view, the ocean floor is colored by depth - deep areas are cool colors and shallow areas are warm colors; the few islands in the scene above sea level are green. The image is 3 times vertically exaggerated.

The Mariana volcanic arc is a chain of underwater volcanoes (seamounts). In this 3D view, the ocean floor is colored by depth — deep areas are cool colors and shallow areas are warm colors; the few islands in the scene above sea level are green. The image is three times vertically exaggerated. Image courtesy of Submarine Ring of Fire 2014 - Ironman, NOAA/PMEL, NSF. Download high-resolution version (2.5 Mb).

Bill Chadwick
Oregon State University and NOAA Pacific Marine Environmental Laboratory

Click to view a computer-generated fly-through movie showing the chain of seamounts that make up the Mariana volcanic arc. The seafloor is colored according to depth, with cooler colors in deeper areas and warmer colors at shallower depths; islands above sea level are green. The bathymetry is three times vertically exaggerated.

Click to view a computer-generated fly-through movie showing the chain of seamounts that make up the Mariana volcanic arc. The seafloor is colored according to depth, with cooler colors in deeper areas and warmer colors at shallower depths; islands above sea level are green. The bathymetry is three times vertically exaggerated. Click image to watch video and for credit information.

Seamounts are underwater mountains, and sometimes they are also active volcanoes. The Mariana Arc is a chain of many seamounts (60) and a few islands (9), which are all active volcanoes. The islands are just the few volcanoes that have grown tall enough to reach above sea level. The seamounts in the Mariana Arc lie hidden below the ocean’s surface, and we are exploring them to find which have active hydrothermal systems and unique biological communities. Many of these seamounts are now part of the Mariana Trench Marine National Monument.

The more we explore in this region, the more amazing animals and environments we discover.

 

Why Are These Volcanoes Here?

Geologic cross-section showing the Pacific Plate (right) subducting beneath the Philippine Plate (left) at the Mariana Trench.  This causes melting that feeds magma to the volcanoes of the Mariana arc.  Image credit: Figure modified from Hussong and Fryer, 1981.

Geologic cross-section showing the Pacific Plate (right) subducting beneath the Philippine Plate (left) at the Mariana Trench. This causes melting that feeds magma to the volcanoes of the Mariana arc. Click image for credit and larger view.

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 near the boundaries of these tectonic plates. 

Where tectonic plates are moving toward each other and colliding, one plate is forced under the other in a process called "subduction." At subduction zones, the down-going plate dives back into the Earth and is eventually melted and recycled. This process causes molten rock (magma) to rise 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, like in the Mariana Arc. 

Map of the all the volcanoes around the Pacific (red triangles), making up the Ring of Fire.

Map of the all the volcanoes around the Pacific (red triangles) making up the Ring of Fire. Click image for credit and larger view.

The "Ring of Fire" is a circular zone of active volcanoes that surrounds the Pacific Ocean basin, mostly along plate boundaries and above subduction zones. Much is known about 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.

 

Hydrothermal Vents and Deep-sea Life

Where submarine volcanoes bring magma near the seafloor or erupt lava at the surface, seafloor hot springs called hydrothermal vents are common. Seawater that circulates deep within a submarine volcano gets heated up before it returns to the seafloor. Hydrothermal vent fluid is rich in chemicals dissolved from the rocks they pass through, and these vents support unique ecosystems of microorganisms and animals that rely entirely on chemical energy for survival. In this way, submarine volcanoes actually support many of Earth’s most unusual ecosystems. 

Our work on this expedition is focused on trying to understand how these ecosystems function and the interactions between volcanic activity, the chemistry of hydrothermal vents, and the ecology of their biological communities.

These mussels, shrimp, and limpets living at NW EIfuku seamount all depend on the chemical energy in hydrothermal vents for survival.  Image credit: Submarine Ring of Fire 2004 Exploration; NOAA/PMEL.

These mussels, shrimp, and limpets living at NW EIfuku seamount all depend on the chemical energy in hydrothermal vents for survival. Image courtesy of Submarine Ring of Fire 2004 Exploration, NOAA/PMEL. Download high-resolution version (3.2 Mb).

 

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