The island of O‘ahu is the leftovers of two volcanoes, Wai‘anae and Ko‘olau. But stretching out nearly 100 km from the western tip of the island of O‘ahu is a sizable region of shallow bathymetry (“submarine topography” or the depths and shapes of underwater terrain), known as the submarine Ka‘ena Ridge, that is the region that has now been identified as a precursor volcano to the island of O‘ahu.