Mariana Back-Arc Segment at 15.5°N Volcano — United States

The Mariana back-arc spreading segment centered at 15.5°N is part of a line of recently surveyed segments with anomalous hydrothermal plumes. The line parallels the Mariana Islands (about 100 km E) and the Mariana Trench (~300 km E). A series of very recently erupted lava flows were discovered in late 2015 along this back-arc zone about 130 km WNW of Saipan. Flows near 15.4°N were not present at the time of a February 2013 bathymetric survey. Large hydrothermal plumes and intense chemical anomalies in the ocean overlie the area. The sediment-free pillow lavas have a dark glassy crust at water depths of between 4,100 and 4,450 m, believed to be the deepest reported eruption known, and the first to be found along a slow-spreading ridge.