Mariana Arc of Fire National Wildlife Refuge

Hydrothermal vents on a volcanic seamount
Three smokers at the bottom of the Mariana Arc of Fire National Wildlife Refuge
Mussels and crabs
Crabs grazing through the mussels

The Mariana Arc of Fire National Wildlife Refuge is located along the Mariana Ridge, an undersea volcanic ridge that marks the Arc of Fire in this part of the Pacific Ocean. The property is composed of 21 non-contiguous parcels, each a circle of land one mile in radius around 21 defined seamounts in the area. The properties constitute an arc of undersea mud volcanoes and thermal vents with back-arc basins, a subduction zone, and numerous active and potentially active island and submerged volcanoes. This is the only area on Earth where huge mud volcanoes spew almost pure hydrogen gas into the water. At the Eifuku submarine volcano a vent spews almost pure carbon dioxide into the water. The pool of liquid sulfur found at the Daikoku submarine volcano is the only such molten sulfur found on Earth. The only other known possibility of that is on Io, a moon circling Jupiter

Bubbles well underwater
Underwater bubbles

The refuge supports life forms that have adapted to exist in some of the harshest conditions imaginable. Many of the vents spew highly acidic water and gases at temperatures up to 570°F (300°C). The area is also unique in that many of the deep sea creatures require basalt in their diet. The creatures also utilize different proteins in their makeup that allow them to eat, breed and reproduce in the temperatures and pressures found at the bottom of the ocean. Some of them thrive nowhere else.

Some areas of the refuge offer zones where photosynthetic and chemosynthetic life come together, where creatures from the deep trade base materials and DNA with creatures of the sunlit zone. Maug Crater is a submerged caldera about 1.5 miles in diameter and 820 feet deep. In the center of the crater is a lava dome that reaches up to 65 feet below the surface. At a depth of 475 feet on the northeast side of the dome are hydrothermal vents spewing highly acidic water at above-boiling temperatures. Very close by is a coral reef thriving with tropical fish.