Geomorphometry and processes that built Necker Ridge, central North Pacific Ocean

• First complete multibeam bathymetry map of Necker Ridge at 100 m/pixel.
• Necker Ridge constructed of stacked volcanic flows capped by 3 carbonate platforms.
• Small conical volcanic pinnacles occur throughout Necker Ridge.
• Four basal flows can be followed more than 600 km along strike of Necker Ridge.
• Lack of pelagic sediment on volcanic flows and saddles between summit platforms.

Necker Ridge is an enigmatic 650-km long, narrow, linear aseismic bathymetric feature that rises 2500 to 3000 m above the abyssal seafloor south of the Hawaiian Ridge. The ridge is the largest of a series of aseismic ridges that emanate from the eastern side of the Mid-Pacific Mountains outward towards the northeast. The trend of Necker Ridge is at an angle to fracture zones and spreading centers in the region, so its origin is controversial, yet it is a major feature on this part of the Cretaceous Pacific Plate. The entire feature, from Necker Island on the Hawaiian Ridge to the eastern Mid-Pacific Mountains, including the adjacent abyssal seafloor, was mapped in 2009 and 2011 with the latest generation of multibeam echosounders. The detailed bathymetry shows the ridge to be constructed of a series of stacked, thick (200–400 m) volcanic flows that can be traced along the trend of Necker Ridge for 100 s of km. This continuity suggests that the volcanism erupted simultaneously along almost the entire length of the feature and not as spatially episodic areas of extrusion. Three relatively flat platforms occur on the summit region, presumably constructed of shallow-water carbonates when these portions of the ridge were at sea level. A conspicuous lack of thick pelagic sediment on the non-platform ridge summit and flanks is seen throughout the ridge. The lack of landslides along the length of the ridge is equally puzzling. The southern end of the ridge is connected by a saddle to the Mid-Pacific Mountains whereas the northern end of the ridge is buried by an archipelagic apron of the southern flank of the Hawaiian Ridge.