Spotlight 9: South Chamorro Seamount

Sixteen large, active serpentinite mud volcanoes exist in the Mariana forearc, the region of seafloor between the Mariana Trench and the volcanic island arc. Up to 50 km in diameter and rising as much as 2.4 km above the surrounding seafloor, these seamounts form as a consequence of subduction processes, which generate deep-seated faults that penetrate the crust and mantle of the overriding Mariana microplate to the depth of the underlying and subducting Pacific plate. Faults are observed up to 100 km west of the Mariana trench and provide a pathway for fluid, released from dehydration reactions within the subducting Pacific plate, and ground-up rock fragments to ascend. As this fluid upwells, it reacts with the overlying mantle, producing serpentine, hydrogen gas, and alkaline fluids (up to pH 12.5).