Mapping the Nuuanu and Wailau landslides in Hawaii
This chapter contains sections titled: introduction seafloor surveys of the nuuanu and wailau landslides discussion
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Geology topics
D. A. Clague
Publications and source records attributed to D. A. Clague.
Petrology of Submarine Lavas from Kilauea's Puna Ridge, Hawaii
We have studied 30 quenched tholeiitic lava flows recovered by 20 dredge hauls and one submersible dive along Puna Ridge, the submarine part of the East Rift Zone of Kilauea Volcano, Hawaii Glass grains from numerous additional flows were recovered in turbidite sands cored in the Hawaiian Trough. These quenched lavas document variable primary magma compositions; olivine and multiphase crystallization and fractionation; degassing; wall-rock stoping and assimilation; mixing in the crustal reservoir and the rift zone; entrainment of olivine xenocrysts from a hot, ductile, olivine cumulate body; and disruption of gabbro wallrocks in the rift zone. Glass grains in turbidite sands contain up to 15⋅0wt% MgO, in contrast to < 7⋅0wt% MgO for the sampled glass rinds on lavas. The most forsteritic olivine phenocryst (F0 90·7 ) is in equilibrium with primary Kilauea liquid containing an average 16⋅5 wt% MgO, but ranging from 13⋅4 to 18⋅4%. Lavas and glass grains have more restricted P 2 O 5 /K 2 O and TiO 2 /K 2 O than glass inclusions in olivine, because more diverse liquids trapped as glass inclusions are mixed and homogenized before eruption. Variable trace element compositions in glass grains and whole rocks indicate that the primary liquids form by partial melting of mantle sources retaining clinopyroxene and garnet. Orthopyroxene xenocrysts formed at moderate pressures provide evidence for a sub-crustal staging zone. Chromite and olivine crystallize in the crustal magma reservoir as the liquid cools from an average 1346°C to ∼1170°C. Low viscosities of the primary liquids (0·4 Pas) facilitate olivine settling, and the crystallized olivine forms an olivine cumulate body at the base of the reservoir. Olivine is deformed as the hot ductile dunite body flows down and away from the summit. This flow drives instability of the Hilina landslide on Kilauea. Dikes intrude the dunite, and magma flowing through the dikes disaggregates and entrains olivine xenocrysts in Puna Ridge magmas. Primary liquids pond at or near the base of Kilauea's crustal reservoir because they are denser than more fractionated liquids that occupy the upper parts of the reservoir. The sulfur and water contents of glass rinds indicate that fractionated liquids near the top of the reservoir degas at low pressure, a process that increases their density and causes them to sink to levels where they mix with resident undegassed, near-primary liquid. The fractionated liquids near the top of the magma reservoir acquire excess Cl, owing to assimilation of hydrothermally altered roofrocks. Magma flowing into the rift zone encounters and mixes with low-temperature, multiphase-fractionated melt. The mixed magmas typically contain rare orthopyroxene, plagioclase as sodic as andesine, olivine as fayalitic as F0 75 and Fe-rich augite derived from the fractionated magma. Magma flowing through dikes also dislodged fragments of gabbroic wallrocks that occur as xenoliths. The interrelations in the Kilauean submarine lavas between host glass and glass inclusion compositions, volatile contents and mineral chemistry reveal an extraordinarily complex sequence of petrogenetic processes and events that are difficult or impossible to determine in subaerial Kilauea lavas because of crystallization, reequilibration and degassing during or after their eruption.
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Subsidence and volcanism of the Haleakala Ridge, Hawaii
Side-looking sonar (GLORIA) mapping has revealed a series of four arcuate bands of high sonic backscatter on the crest of the Haleakala Ridge, a major rift-zone ridge extending 135 km east of the island of Maui. Dredge recovery indicates that the shallowest of these bands is a drowned coral reef, and the deeper bands are also inferred to be coral reefs. The reefs occur above a prominent submarine bench 1500–2500 m deep on the ridge (H-terrace) that marks the shoreline at the end of vigorous shield building of Haleakala volcano when lava flows ceased crossing and reworking the shoreline. Since their growth these reefs have subsided as much as 2200 m and have tilted systematically about 20 m/km southward as a result of post-reef volcanic loading on the island of Hawaii, whose center of mass is about directly south of the Haleakala Ridge. The 234 U/ 238 U age of the dredged coral is 750 ± 13 ka "> 750 ± 13ka , in reasonable agreement with an age of 850 ka for the underlying H terrace previously estimated from its relationship to other dated reefs to the southwest. Basalt glass fragments dredged from the Haleakala Ridge below the H terrace are tholeiitic and contain high sulfur indicative of eruption in water deeper than 200 m. Basalt glass fragments associated with the reefs above the H terrace are dominantly tholeiitic and contain intermediate sulfur contents, indicative of subaqueous eruption in shallow, near-shore conditions. One alkalic glass fragment was recovered above the H terrace. These relations indicate that the morphologic end of shield building as recorded by construction of the H terrace was not accompanyed by a change from tholeiitic to alkalic basalt; instead tholeiite eruptions continued for some time before the erupted lava became alkalic.
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Diverse basalt types from Loihi seamount, Hawaii
Loihi seamount is the southeasternmost active volcano in the Hawaiian-Emperor volcanic chain. The seamount is considered representative of the early phase of Hawaiian volcanism because of its youth, small size, and location near the melting anomaly. Seventeen dredge stations recovered transitional basalt, alkalic basalt, and basanite, in addition to the expected tholeiitic basalt. Four flows of alkalic basalt contain common small dunite xenoliths. The recovered samples have thin palagonite rinds and almost no manganese on the glassy surfaces; we estimate that the lavas are less than about 4,000 yr old, and many are less than 1,000 yr old. Loihi seamount is apparently in a transitional growth phase between the early eruption of alkalic lavas and the commonly observed (subaerial) tholeiitic eruptive phase, previously thought to dominate Hawaiian volcanism from inception until the postcaldera collapse, alkalic stage.
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