Studies on the bathyal fauna of northern Pacific waters suggested that a transition or boundary between the North Pacific Province and Central Pacific Provinces would be found somewhere along the Emperor Seamount Chain. Strong currents flowed west to east across the seamount chain in a region known as the Main Gap and it was proposed that any larvae produced either north or south of the Main Gap would not be capable of crossing the gap. An expedition to test the hypothesis that a faunal change would be found in the vicinity of the Main Gap was conducted in 2019. Eleven ROV dives were conducted, one on an unnamed seamount at the southern edge of Hess Rise, and 10 dives on seven seamounts along the Emperor Seamount Chain. Six dives were on seamounts north of the Main Gap, while four (including the dive on Hess Rise) were on the southern side. Of the six northern dives, three were at deeper depths (∼2000 – 1800 m) and three were shallower (∼1500 – 1100 m); of the southern dives two were at the deeper depths and two were shallower. One shallower dive occurred on Jingu Seamount, situated on the southern edge of the Main Gap. Analysis of the fauna from both collected specimens and annotations of the dive video produced four clusters: a, the four dives south of the Main Gap; b, the three deeper dives north of the Main Gap; c, the shallower dive at Jingu Seamount; and d, the four shallower bathyal dives north of the Main Gap. It was concluded that the bathyal fauna underwent a significant change from north to south across the area of the Main Gap and the adjacent Small Gap, in the area of 37 – 39 °N, covering distances as small as 75 km or as much as 400 km.

New bathymetric and gravity mapping, refined volume calculations and petrologic analyses show that the Hawaiian volcano Pūhāhonu is the largest and hottest shield volcano on Earth. This ∼12.5-14.1 Ma volcano in the northwest Hawaiian Ridge (NWHR) is twice the size of Mauna Loa volcano (148 ± 29 vs. 74.0×103km3), which was assumed to be not only the largest Hawaiian volcano but also the largest known shield volcano. We considered four testable mechanisms to increase magma production, including 1) thinner lithosphere, 2) slower propagation rate, 3) more fertile source, and 4) hotter mantle. The first three of these have been ruled out. The lithosphere was old (∼88 Myrs) when Pūhāhonu was formed, and thus, too thick and cold to allow for greater extents of partial melting. The propagation rate was relatively fast when it erupted (87 km/Myr), so this is another unlikely reason. Source fertility was Kea-like and no more fertile than for other much smaller NWHR volcanoes. A hotter mantle remains the best mechanism to produce the large magma volumes and is consistent with the high forsteritic olivine phenocryst compositions (up to 91.8%) and the calculated high percent of melting (24%). Thus, the gargantuan size of Pūhāhonu reflects its high melting temperature, the highest reported for any Cenozoic basalt. A solitary wave within the Hawaiian plume is the probable cause of Pūhāhonu's higher melting temperature and the resulting increased volume flux given the absence of a more fertile source for Pūhāhonu basalts, as found for many basalts from the Hawaiian Islands.

The Northwest Hawaiian Ridge is a classic example of a large igneous province. The morphology and geology of the ridge is poorly characterized, although it constitutes the longest segment (similar to 47%) of the Hawaiian-Emperor Chain. Here we present a new bathymetric compilation, petrographic and X-ray fluorescence (XRF) data for lavas from 12 volcanoes along the Northwest Hawaiian Ridge, and review literature data for the age and isotopic variation of the ridge. The bathymetric compilation revealed that the Northwest Hawaiian Ridge consists of at least 51 volcanoes. The 45 new XRF analyses show that the Northwest Hawaiian Ridge contains tholeiitic and alkalic lavas with compositions typical of lavas from the Hawaiian Islands. The absolute ages and duration of volcanism of individual Northwest Hawaiian Ridge volcanoes are poorly known, with modern Ar-40/Ar-39 ages for only 10 volcanoes, mostly near the bend in the chain. We infer the initiation age of the Hawaiian-Emperor Bend to be ca. 49-48 Ma, younger than the age for the onset of island arc volcanism in the western Pacific (52-51 Ma). Thus, the kink in the Hawaiian-Emperor Chain and the onset of arc volcanism were not synchronous. Isotopic data are sparse for the Northwest Hawaiian Ridge, especially for Pb and Hf. Two transitional lavas from just south of the bend have Loa trend type Pb and Sr isotopic ratios. Otherwise, the available chemistry for Northwest Hawaiian Ridge lavas indicates Kea-trend source compositions. The dramatic increase in melt flux along the Hawaiian Ridge (similar to 300%) may be related to changes in melting conditions, source fertility, or plate stresses.

Large volcanic edifices constitute enormous loads at the surfaces of planets. The lithosphere, the mechanically strong outer layer of a planet, responds to growing edifice loads by flexing. The shape of this lithospheric flexure and the resulting stress state exert critical influences on the structure of the evolving edifices, which in turn feed back into the flexural response. Flexural subsidence of the lithosphere forms topographical moats surrounding volcanoes that are partially to completely filled by landslide debris, volcaniclastic materials and sediments, or by relatively flat aprons of volcanic flows. Flexure creates a characteristic 'dipole' state of stress that influences subsequent magma ascent paths and chamber dynamics in the lithosphere. Compression in the upper lithosphere can inhibit magma ascent and favour the development of oblate magma chambers or sill complexes. This compression can be transferred into the edifice unless a decollement allows the volcano base to slip over the underlying lithosphere; generally, basal decollements are found to operate via high pore-fluid pressure in a clay sediment-based layer. Volcanoes lacking such a layer, regardless of the thickness of the basal sediments, lack basal decollements and, thus, tend to be limited in size by compressive stresses adverse to magma ascent.

The South Kaua‘i Swell (SKS) is a 110 km x 80 km ovoid bathymetric feature that stands >2 km high and abuts the southern flank of the island of Kaua‘i. The origin of the SKS was investigated using multibeam bathymetry and acoustic backscatter, gravity data, radiometric ages, and geochemistry of rock samples. Most of the SKS rock samples are tholeiitic in composition with ages of 3.9–5.4 Ma indicating they were derived from shield volcanism. The ages and compositions of the SKS rocks partially overlap with those of the nearby Ni‘ihau, Kaua‘i and West Ka‘ena volcano complexes. The SKS was originally described as a landslide; however, this interpretation is problematic given the ovoid shape of SKS, its relatively smooth, flat‐to‐convex surface, and the lack of an obvious source region that could accommodate what would be one of Earth's most voluminous (6 x 103 km3) landslides. The morphology, size, and the surrounding gravity anomaly are more consistent with the SKS being a low‐relief shield volcano, which was partially covered with a small volume of landside debris from south Kaua‘i and later with some secondary volcanic seamounts. A shield origin would imply that Hawaiian and possibly other hotspot shield volcanoes can take on a wider variety of forms than is commonly thought, ranging from tall island‐building shields, to smaller edifices such as Ka‘ena Ridge and Mahukona, to even lower‐relief volcanoes represented by the SKS and possibly the South West O‘ahu Volcanic Field.

We present the geomorphology of the Eastern Samoa Volcanic Province, covering 28,446 km(2), and depths ranging from similar to 50 to 4,000 m. A new compilation of available multibeam data reveals 51 previously undocumented seamounts, and delineates major submarine rift zones, eruptive centers, and volcanic plateaus. Moving from a regional to local scale, and with regard to specific coral reef habitats, we report the results of three Pisces V submersible dives to the submerged flanks of Tutuila, with overall objectives of species identification of deep water fish and invertebrates (32 species of invertebrates and 91 species of fish identified, 9 new records), determining the base of extensive live bottom (i.e., coral cover of 20% and greater) as well as relations to any prior benthic terrain classifications at 100 m and deeper.

This database release, USGS Data Series 171, contains data collected during four Japan-USA collaborative cruises that characterize the seafloor around the Hawaiian Islands. The Japan Agency for Marine-Earth Science and Technology (JAMSTEC) sponsored cruises in 1998, 1999, 2001, and 2002, to build a greater understanding of the deep marine geology around the Hawaiian Islands. During these cruises, scientists surveyed over 600,000 square kilometers of the seafloor with a hull-mounted multibeam seafloor-mapping sonar system (SEA BEAM® 2112), observed the seafloor and collected samples using robotic and manned submersible dives, collected dredge and piston-core samples, and performed single-channel seismic surveys.

We present detailed bathymetry, remotely operated vehicle (ROV) and submersible observations, and sedimentary and radiocarbon age data from carbonate deposits recovered from two submerged terraces at − 150 m (T1) and − 230 m (T2) off Lanai, Hawaii. The tops of the terraces are veneered by relatively thin (< 5 m) in situ accumulations of coralline algal nodule, coralgal nodule, Halimeda and a derived oolitic facies deposited in intermediate (30–60 m) to deep fore-reef slope settings (60–120 m). The data are used to develop a sedimentary facies model that is consistent with eustatic sea-level variations over the last 30 ka. Both nodule facies on T1 and T2 initiated growth 30–29 ka following a fall in sea level of ∼50 m and increase in bottom currents during the transition from Marine Isotope Stage 3 to 2. The nodules accreted slowly throughout the Last Glacial Maximum when sea-level was relatively stable. Drowning occurred during the early deglaciation (17–16 ka) and was marked by the complete drowning of coralline algal nodules facies on T2 and incipient drowning of coralgal facies on T1. Abrupt sea-level rise during the middle deglaciation, perhaps associated with global meltwater pulse 1A (14–15 ka), finally drowned the coralgal facies on T1, which in turn was overlain by a deep-water Halimeda facies or an oolitic facies derived from upslope. Our data indicates that Lanai has experienced relatively little vertical tectonic movement over the last 30 ka. Using paleobathymetric data derived from the sedimentary facies, age vs. depth relationships, and published sea-level curves, we estimate that Lanai could be either slowly uplifting or subsiding, but at rates < 0.1 m/kyr (uplift) or < 0.4 m/kyr (subsidence) over this 30 kyr period.

The rapid mass wasting of shallow submarine basalts was documented during SCUBA dives along the flanks of Kilauea volcano, Hawaii during the Kii lava entry of the current eruption (19°20.5′N, 154°59.8′W). Lava entered the ocean at this site from mid-February to late March 1990, with several pauses. Dives on 19–20 March 1990 confirmed the widespread formation of lava pillows at this site over a water depth range of 20–40 m, and visual observations suggested that the resulting volcanic deposits were generally stable, despite the steep (∼40°) incline of the seafloor. (The pre-eruptive nearshore seafloor slope was ∼14°.) However, dives on 2 April 1990 revealed that nearly all submarine volcanic features had been subject to mass wasting, as the offshore area had been transformed into a debris field composed of material ranging in size from fine sand to boulder fragments. This generally featureless seascape extended uniformly to beyond the visual range of divers (∼60 m water depth). High-resolution multibeam bathymetry and sidescan imaging indicate that steeply sloped coarse sediment extends down the flanks of Kilauea in this area to abyssal depths, implying a linkage between nearshore submarine volcanism and deep-water deposits.

Additional reading: Decker, R.W., Wright, T.L., and Stauffer, P.H., eds., 1987, Volcanism in Hawaii: U.S. Geological Survey Professional Paper 1350, 2 v., 1667 p. Francis, Peter, 1993, Volcanoes—A planetary perspective: Oxford, Clarendon Press, 433 p. Heliker, Christina, Swanson, D.A., and Takahashi, T.J., eds., 2003, The Pu‘u ‘O‘o-Kupaianaha eruption of Kilauea Volcano, Hawai‘i—The first 20 years: U.S. Geological Survey Professional Paper 1676, 206 p. Macdonald, G.A., Abbott, A.T., and Peterson, F.L., 1983, Volcanoes in the sea—The geology of Hawaii (2d ed.): Honolulu, University of Hawai‘i Press, 517 p. Rhodes, J.M., and Lockwood, J.P., eds., 1995, Mauna Loa revealed—Structure, composition, history, and hazards: American Geophysical Union Geophysical Monograph 92, 348 p. Smith, W.H.F., and Sandwell, D.T., 1997, Global seafloor topography from satellite altimetry and ship depth soundings: Science, v. 277, p. 1957-1962. Takahashi, Eiichi, Lipman, P.W., Garcia, M.O., Naka, Jiro, and Aramaki, Shigeo, eds., 2002, Hawaiian volcanoes—Deep underwater perspectives: American Geophysical Union Geophysical Monograph 128, 418 p. Tarduno, J.A., Duncan, R.A., Scholl, D.W., Cottrell, R.D., Steinberger, Bernard, Thordarson, Thorvaldur, Kerr, B.C., Neal, C.R., Frey, F.A., Torii, Masayuki, and Carvallo, Claire, 2003, The Emperor Seamounts—Southward motion of the Hawaiian hotspot plume in Earth's mantle: Science, v. 301, p. 1064-1069. _ _ _

Ancestral Submarine Growth of Kïlauea Volcano and Instability of its South Flank Peter W. Lipman, Peter W. Lipman Volcano Hazards Program, U.S. Geological Survey, Menlo Park, CaliforniaSearch for more papers by this authorThomas W. Sisson, Thomas W. Sisson Volcano Hazards Program, U.S. Geological Survey, Menlo Park, CaliforniaSearch for more papers by this authorTadahide Ui, Tadahide Ui Graduate School of Science, Hokkaido University, Sapporo, JapanSearch for more papers by this authorJiro Naka, Jiro Naka Japan Marine Science and Technology Center, Yokosuka, JapanSearch for more papers by this authorJohn R. Smith, John R. Smith School of Ocean and Earth Science and Technology, University Of Hawai'i, Honolulu, Hawai'iSearch for more papers by this author Peter W. Lipman, Peter W. Lipman Volcano Hazards Program, U.S. Geological Survey, Menlo Park, CaliforniaSearch for more papers by this authorThomas W. Sisson, Thomas W. Sisson Volcano Hazards Program, U.S. Geological Survey, Menlo Park, CaliforniaSearch for more papers by this authorTadahide Ui, Tadahide Ui Graduate School of Science, Hokkaido University, Sapporo, JapanSearch for more papers by this authorJiro Naka, Jiro Naka Japan Marine Science and Technology Center, Yokosuka, JapanSearch for more papers by this authorJohn R. Smith, John R. Smith School of Ocean and Earth Science and Technology, University Of Hawai'i, Honolulu, Hawai'iSearch for more papers by this author Book Editor(s):Eiichi Takahashi, Eiichi TakahashiSearch for more papers by this authorPeter W. Lipman, Peter W. LipmanSearch for more papers by this authorMichael O. Garcia, Michael O. GarciaSearch for more papers by this authorJiro Naka, Jiro NakaSearch for more papers by this authorShigeo Aramaki, Shigeo AramakiSearch for more papers by this author First published: 01 January 2002 https://doi.org/10.1029/GM128p0161Citations: 23Book Series:Geophysical Monograph Series AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onFacebookTwitterLinked InRedditWechat Summary This chapter contains sections titled: Introduction Geologic Setting Stratigraphy and Structure of the Submarine South Flank Compositions of Breccia Clasts, Breccia Matrix, and Sandstones Submarine Growth of Ancestral Kilauea Ages of Early Events: Isotopic Dating and Piston-Core Stratigraphy Other Possible Sites of Early Alkalic Volcanism Past Slope Failures and Future Stability of the South Flank Citing Literature Hawaiian Volcanoes: Deep Underwater Perspectives, Volume 128 RelatedInformation

This chapter contains sections titled: Introduction Previous Multibeam Work Seabeam 2112 System Description Survey Areas Guide to the CD-Rom

The Koolau and East Molokai volcanoes are reconstructed and the volume changes associated with the Nuuanu and Wailau landslides are estimated. An objective and universal method is developed and applied to the digital bathymetric data obtained during recent cruises. Because the location of the headwall immediately after the landslides is poorly known, we model both subaerial and submarine headwalls. For the Wailau landslide, the missing slide volume is 1.5x 10 3 km 3 for the subaerial headwall and 0.8 x 10 3 km 3 for the submarine headwall. The total volume of the excess debris deposit is estimated as 1.5 x 10 3 km 3 . For the Nuuanu landslide, the slide volume is approximately 3 x 10 3 km 3 for the subaerial headwall and 2 x 10 3 km 3 for the submarine headwall. The debris volume is estimated as 3 x 10 3 km 3 . Tsunami generation and propagation from these landslides are computed on the present-day bathymetry. The tsunami reaches most of the Hawaiian Islands within half an hour from slide onset. Tsunami heights from the Nuuanu landslide are greater than 100 m on the northern coasts of Oahu and Molokai islands, and 20 - 30 m on the southern coasts. The tsunami arrives on the West Coast of North America in about 5 hours and Japan in 8 hours. The Nuuanu tsunami is strongly directed toward southern California where the tsunami heights would be as large as 70 m. The tsunami arrival times from the Wailau landslide are similar, butthe water heights are about 60 - 70 % of those from the Nuuanu landslide and are differently oriented.

This chapter contains sections titled: Introduction Emplacement and Inflation of Flow-Lobe Tumuli And Pahoehoe Lobes Lobe Emplacement And Lava Supply Rates Discussion Conclusion

This chapter contains sections titled: Introduction Methods Northeast Flanks of Kohala and Mauna Kea Hana Ridge Hilo Ridge Discussion Conclusions

This chapter contains sections titled: Introduction Geological Setting and Sampling Sites Textures and Compositions of Volcaniclastic Fragments Origin of the Volcaniclastic Layers Sediment Source and Depositional Processes on the South Flank Events Recorded in Piston Cores Summary