About the Refuge

Brimstone Pit

Called Brimstone Pit, the pressure of 1,837 feet of water over the site reduces the power of the explosive bursts. Also, the water quickly slows down the rocks and ash that are violently thrown out of the vent.


The Mariana Trench National Wildlife Refuge is located in the Western Pacific 3,520 miles west-southwest of Honolulu, Hawai‘i, and neighboring the Mariana Archipelago. 

The crescent-shaped Mariana Trench, stretching approximately 940 nautical miles and 38 nautical miles wide from the northern limit of the U.S. Exclusive Economic Zone in the Commonwealth of the Northern Mariana Islands to the southern limit of the U.S. EEZ in Guam, was designated as part of the Marianas Trench Marine National Monument on January 6, 2009, through Presidential Proclamation 8335. These submerged lands are managed as a unit of the National Wildlife Refuge System in accordance with Secretary’s Order 3284, which created the refuge on January 16, 2009.

The Mariana Trench was created geologically as the Pacific Plate plunged beneath the Philippine Sea Plate and into the Earth’s mantle and contains some of the deepest known points in the global ocean. The Mariana Trench is also recognized by the international scientific community as the oldest place geologically on the floor of any ocean on earth. Due to its inaccessibility, the region is virtually unexplored, and much remains to be learned about its ecological and biological characteristics.

The ocean floor at such depth consists of a type of pelagic sediment known as biogenous "ooze." Biogenic pelagic sediment is composed of the shells (tests, frustules) of microscopic plankton, both animal (zooplankton) and plant (phytoplankton) plankton.