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Mapping an Unnamed Seamount SE of Pearl and Hermes Atoll
By Jonathan R. Weiss
Seafloor Mapping Specialist
NOAA Coral Reef Ecosystem Division

Multi-beam mapping aboard the NOAA Ship Hiialakai during the recent coral bleaching Cruise in the Northwestern Hawaiian Islands (NWHI) has enabled NOAA scientists to create images of the seafloor such as these, in locations where little data were previously available. For example, prior to the cruise, the seamount in these images, located southeast of Pearl and Hermes Atoll, NWHI, was unmapped and only one forty fathom (-73 m) sounding existed in its vicinity.

There is over 2000 m of relief between the top of the seamount at -105 m and the surrounding seafloor. The northwest-trending ridge connecting the seamount to Pearl and Hermes atoll suggests a linked geologic history between the two submarine mountains. The small peaks on top of the ridge might suggest the presence of ancient volcanic centers and the hummocky topography on the north face of the ridge may be slump blocks. Additional linear ridges radiate from the northern and southwestern apices of the triangular-shaped seamount in a fashion similar to submarine volcanic rift zones such as the southeast rift zone of the active Kilauea Volcano on Hawaii Island. The flat-topped nature of the seamount suggests it was planed off by erosion at sea level tens of millions of year ago and has since subsided to its present depth as the Pacific tectonic plate moves to the northwest.

In addition to the geologic significance of the data, it is of biological and resource management importance as well. For example, the location of the newly mapped seamount is associated with monk seal foraging sites, and the data around Pearl and Hermes Atoll will aid in NWHI Coral Reef Ecosystem Reserve boundary determination. This is just one of many exciting new pieces of information gained through the combined efforts of NOAA’s National Marine Sanctuary Program and Coral Reef Ecosystem Division.