Ni`ihau survey
The Ni`ihau survey imaged a region of young lava flows and volcanic cones on the submarine northwest flank of Ni`ihau Island. More than half of Ni`ihau Island consists of rejuvenated-stage alkalic basalt flows and cones of the Kiekie Volcanics (Stearns and Macdonald, 1947; Clague, 1987) and the submarine volcanic cones and flows are almost certainly related to them. The Kiekie Volcanics have been dated by potassium-argon techniques at 0.3-3.5 million years old (Clague and Dalrymple, 1987), and the submarine lava flows and cones, although unsampled, probably formed during this same time period.
The volcanic cones have unusual shapes with steep flanks and nearly flat tops that probably formed as submarine lava ponds overflowed levees, creating the circular shape and the flat top (Clague et al., 1999, in press). Such flat-topped volcanic cones had not previously been identified from the flanks of any of the Hawaiian Islands. A few cones have pointed tops and may be related to post-shield stage eruptions of volatile-rich alkalic basalt.
The new data also show an old shoreline of the island, probably formed near the end of the voluminous tholeiitic shield stage, as a sharp break-in-slope around 1,000 meters depth. The depth of this shoreline feature indicates the amount of subsidence that Ni`ihau Island has undergone since the end of the shield-building stage. In addition, the break-in-slope is deeper to the northeast (1,090 meters) than to the southwest (960 meters), indicating that Ni`ihau subsided more on the end closest to the adjacent Kauai Island. Several irregular-shaped cones are present on the gently-sloping platform above the break-in-slope.
The images below are map views of the bathymetry and backscatter data and several oblique views. The first of the oblique views is from the north, the second is a close-up from the same direction, and the final view is from the west. The oblique images are sun-illuminated bathymetry with a color scale superposed and the backscatter draped on the sun-illuminated bathymetry.
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 Map view 1 |
 Map view 2 |
 Map view 3 |
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 Oblique view 1 |
 Oblique view 2 |
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 Oblique view 3 |
 Oblique view 4 |
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 Oblique view 5 |
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| Index Map | Haleakala | Hilo | Kohala | Loihi | Mahukona | Moloka`i | Ni`ihau | Papa`u | Puna Ridge |