Hawaii's Volcanoes Revealed

The Japan Agency for Marine-Earth Science and Technology (JAMSTEC) funded and led a four-year collaborative survey of the underwater flanks of Hawaii's shield volcanoes. This exploration, involving scientists from the U.S. Geological Survey (USGS) and other Japanese and U.S. academic and research institutions, used manned and unmanned submersibles, rock dredges, and sediment piston cores to directly sample and visually observe the seafloor at specific sites.

Ship-based sonar systems were used to map the bathymetry from the sea surface more widely. The state-of-the-art multibeam sonar systems, mounted on the hull of GPS-navigated research vessels, convert the two-way travel times of individual sonar pings and their echoes into a line of bathymetry values across the ship track. The resulting swaths across the ocean bottom, obtained along numerous overlapping ship tracks, reveal the seafloor in stunning detail.

The survey data collected by JAMSTEC forms the basis for the bathymetry shown on the map, augmented with bathymetric data from other sources. Bathymetry that is predicted from variations in sea-surface height, observable from satellites, provides the low-resolution (fuzzy) bathymetry in between ship tracks. Subaerial topography is from a 30-meter USGS digital elevation model of Hawaii. Historical lava flows are shown in red. Prominent terraces (shown in orange and yellow) illustrate the larger size of the islands in the past. O'ahu and the Maui-Nui complex (Maui, Moloka'i, Lāna'i, and Kaho'olawe islands and Penguin Bank), in particular, are mere vestiges of their former extent. Lō'ihi, the youngest volcano in the chain, has not yet reached the sea surface.

Fields of blocky debris, such as Ko'olau's Nu'uanu Slide, were created by catastrophic landslides, which carried large parts of some volcanoes as much as 200 kilometers across the seafloor. In contrast, slower-moving, sediment-blanketed slumps typically develop ridges that parallel the paleo coastlines such as Haleakalā's Hana Slump. Eruptions along the submarine part of a volcano's rift zone produce a rugged morphology, as at Kīlauea's Puna Ridge. Numerous seamounts of late Cretaceous age are scattered across the deep-sea floor and are unrelated to the hot spot that supplies Hawaii's volcanoes.