Lō'ihi Seamount

Lō`ihi Seamount defines the volcanically active, leading edge in the Hawaiian hotspot chain. It is located on the submarine flank of Mauna Loa, 30 km south of the island of Hawai`i. Lō`ihi’s summit is at 975-m water depth (Pisces Peak), and the seamount has a pronounced southern rift that extends down to about 5000-m water depth (Figure 1). The summit displays three pit craters (Figure 1), including Pele’s Pit (1350-m water depth), the most hydrothermally active crater, which was formed during an earthquake swarm in 1996 (Garcia et al., 2006). Lō`ihi was not recognized as an active volcano until a sampling expedition in 1978 that led to a detailed understanding of Lō`ihi as a juvenile oceanic intraplate volcano; it then became the de facto type location for the first stage in the development of a typical oceanic intraplate volcano (Figure 2; Moore et al., 1982; Staudigel et al., 1984; Koppers and Watts, 2010). Key characteristics of this “Lō`ihi Stage” of ocean island formation include: (1) a very small volume relative to the final completed volcano, (2) a diverse suite of rock types ranging from very alkalic to tholeiitic, and (3) heterogeneous mantle sources. Since then, Lō`ihi has been the focus of substantial scientific research, with numerous sampling expeditions, leading to a detailed understanding of its volcanic history, seismic activity, petrology, geochemistry, and microbiology (see review by Garcia et al., 2006; Emerson et al., 2007; http://en.wikipedia.org/wiki/Loihi_Seamount)

Researchers Rapidly Respond to Submarine Activity at Loihi Volcano, Hawaii

The largest swarm of earthquakes ever observed at a Hawaiian volcano occurred at Loihi Seamount during July and early August 1996. The earthquake activity formed a large summit pit crater similar to those observed at Kilauea, and hydrothermal activity led to the formation of intense hydrothermal plumes in the ocean surrounding the summit. To investigate this event, the Rapid Response Cruise (RRC) was dispatched to Loihi in early August and two previously planned LONO cruises (named for a Hawaiian warrior god) sailed in September and October on the R/V Kaimikai-O-Kanaloa. Calm weather and a newly refurbished ship provided excellent opportunities for documenting the volcanic, hydrothermal plume, vent, and biological activities associated with the earthquake swarm

Submarine volcanic morphology of the western Galapagos based on EM300 bathymetry and MR1 side-scan sonar

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 8 (2007): Q03010, doi:10.1029/2006GC001464.A compilation of high-resolution EM300 multibeam bathymetric and existing MR1 side-scan sonar data was used to investigate the volcanic morphology of the flanks of the western Galápagos Islands. The data portray an assortment of constructional volcanic features on the shallow to deep submarine flanks of Fernandina, Isabela, and Santiago Islands, including rift zones and groups of cones that are considered to be the primary elements in constructing the archipelagic apron. Ten submarine rift zones were mapped, ranging in length from 5 to 20 km, comparable in length to western Canary Island rift zones but significantly shorter than Hawaiian submarine rift zones. A detailed analysis of the northwestern Fernandina submarine rift, including calculated magnetization from a surface-towed magnetic study, suggests that the most recent volcanism has focused at the shallow end of the rift. Small submarine volcanic cones with various morphologies (e.g., pointed, cratered, and occasionally breached) are common in the submarine western Galápagos both on rift zones and on the island flanks where no rifts are present. At depths greater than ∼3000 m, large lava flow fields in regions of low bathymetric relief have been previously identified as a common seafloor feature in the western Galápagos by Geist et al. (2006); however, their source(s) remained enigmatic. The new EM300 data show that a number of the deep lava flows originate from small cones along the mid-lower portion of the NW submarine rift of Fernandina, suggesting that the deep flows owe their origin, at least in part, to submarine rift zone volcanism.Data collected on TN188 was funded by NSF grant OCE0326148 and NOAA grant NA04OAR460009 to S.M.W. Support for data collected on previous multibeam and MR1 cruises was provided by NSF grants OCE9811504 and OCE0002461 (D.J.F.)

Fore-arc deformation and underplating at the northern Hikurangi margin, New Zealand

Geophysical investigations of the northern Hikurangi subduction zone northeast of New Zealand, image fore‐arc and surrounding upper lithospheric structures. A seismic velocity (Vp) field is determined from seismic wide‐angle data, and our structural interpretation is supported by multichannel seismic reflection stratigraphy and gravity and magnetic modeling. We found that the subducting Hikurangi Plateau carries about 2 km of sediments above a 2 km mixed layer of volcaniclastics, limestone, and chert. The upper plateau crust is characterized by Vp = 4.9–6.7 km/s overlying the lower crust with Vp > 7.1 km/s. Gravity modeling yields a plateau thickness around 10 km. The reactivated Raukumara fore‐arc basin is >10 km deep, deposited on 5–10 km thick Australian crust. The fore‐arc mantle of Vp > 8 km/s appears unaffected by subduction hydration processes. The East Cape Ridge fore‐arc high is underlain by a 3.5 km deep strongly magnetic (3.3 A/m) high‐velocity zone, interpreted as part of the onshore Matakaoa volcanic allochthon and/or uplifted Raukumara Basin basement of probable oceanic crustal origin. Beneath the trench slope, we interpret low‐seismic‐velocity, high‐attenuation, low‐density fore‐arc material as accreted and recycled, suggesting that underplating and uplift destabilizes East Cape Ridge, triggering two‐sided mass wasting. Mass balance calculations indicate that the proposed accreted and recycled material represents 25–100% of all incoming sediment, and any remainder could be accounted for through erosion of older accreted material into surrounding basins. We suggest that continental mass flux into the mantle at subduction zones may be significantly overestimated because crustal underplating beneath fore‐arc highs have not properly been accounted for

Crustal and Upper Mantle Structure of the Solomon Islands as Revealed by Seismic Refraction Survey of November-December 1966

A seismic refraction survey was carried out in the waters around the Solomon Islands during November and December 1966. Three ships were involved in the survey: two, stationed at the end points of the traverses, acted as recording ships; the third steamed along the traverses and dropped explosives. Reflection profiling and magnetic surveys were simultaneously carried out with the refraction survey. The results show that (a) on the Ontong Java Plateau to the northwest of the islands the crust is about 25 km thick with subnormal crustal velocities; (b) southwest of the New Georgia Islands the crust is thinner than normal and is underlain by a mantle with low velocity; (c) southwest of Bougainville Island the crust is generally of normal oceanic structure underlain by a mantle with low velocity; and (d) mantle material in the Slot is found at a depth of 14 km