Senshu Guyot

It's a flat-topped undersea mountain, or guyot, on the North Pacific Ocean floor, officially recognized as a named feature in the GEBCO Gazetteer of Undersea Feature Names. Its flat top is the giveaway of its volcanic guyot origin rather than a peaked seamount.

A guyot began as a volcanic island whose summit was flattened by wave erosion at sea level. As the oceanic plate cooled and subsided, the eroded volcano sank, leaving the flat top hundreds or thousands of meters beneath the surface.

GEBCO, the General Bathymetric Chart of the Oceans, is an international seafloor-mapping project dating back to 1903. Its gazetteer is the reference list of standardized names for undersea features like Senshu Guyot, maintained under the auspices of the International Hydrographic Organization and UNESCO's ocean commission.

Senshu is a traditional regional name for the southern Osaka area of Japan, and Japanese regional names are commonly applied to seafloor features in the northwest Pacific. The naming follows international conventions so that charts and scientific literature use one consistent label.