2003/2006 Mariana Arc
Distribution of hydrothermally active volcanoes
Submarine volcanic arcs extend for fully a third of the length of the mid-ocean ridge system, but systematic investigation of hydrothermal venting on those arcs is sparse. In 2003 and 2004 we conducted an extensive exploration for hydrothermal activity along the intraoceanic Mariana arc. From these surveys we identify 76 volcanic edifices along 1370 km of arc, grouped into 60 ‘‘volcanic centers,’’ of which at least 26 (20 submarine) are hydrothermally or volcanically active. The overall volcanic center density is 4.4/100 km of arc, and that of active centers is 1.9/100 km. An equal length of the Tonga-Kermadec arc holds fewer centers, 2.9/100 km, but a similar density of active centers, 1.8/100 km. Active centers are found from 80 to 230 km above the subducting Pacific slab, and a quarter lie behind the arc front. The frequency distribution of center spacing along the arc front peaks between 20 and 30 km, and there is no evidence for a regular spacing of volcanic centers. Using the new Mariana data and recent data from the Tonga-Kermadec arc, we estimate that all intraoceanic arcs combined may contribute hydrothermal emissions equal to ~10% of that from the global mid-ocean ridge.
Baker, E. T., R. W. Embley, S. L. Walker, J. A. Resing, J. E. Lupton, K.-I. Nakamura, C. E. J. de Ronde, and G. J. Massoth (2008), Hydrothermal activity and volcano distribution along the Mariana arc, J. Geophys. Res., 113, B08S09, doi:10.1029/2007JB005423. (PDF)
Volcanic ash transport from NW Rota-1
NW Rota-1 is an active submarine volcano in the Mariana Arc with a summit depth of 517 m and an explosively erupting volcanic vent southwest of the summit at a depth of 530–560 m. During periods of ongoing explosive eruptions, particle plumes can surround the volcano. At least 3.3 x 107 m3 of volcaniclastic material was deposited on the southern flank between 2003 and 2006. Particle plumes over the summit are magmatic-hydrothermal in origin characterized by 3He enrichment, hydrothermal precipitates, and low pH values. Plumes at multiple depths below the summit surround the volcano and are composed overwhelmingly of fresh, glassy shards of basalt. Rare anhydrite particles are present, indicating that the source of the deep plumes is at the eruptive vent, and that the downslope transport must be far faster than settling of individual particles. The deep plumes most likely originate from sediment gravity flows generated by explosive eruptions or slope failure and landslides of unstable materials that accumulate near the eruptive vent. These observations link mechanisms for the transport of volcanic ash in the submarine environment to the types of deposits common in volcaniclastic aprons and fine ash layers in distal sediments.
Walker, S. L., E. T. Baker, J. A. Resing, W. W. Chadwick Jr., G. T. Lebon, J. E. Lupton, and S. G. Merle (2008), Eruption-fed particle plumes and volcaniclastic deposits at a submarine volcano: NW Rota-1, Mariana Arc, J. Geophys. Res., 113, B08S11, doi:10.1029/2007JB005441. (PDF)