Kaûena Ridge, also referred to as the Kaûena Volcano, is a submerged remnant of an ancient shield volcano that is to the north of and once comprised the northern section of the Hawaiian Island of Oûahu.
Kaûena Ridge was the oldest of the three volcanoes to form Oûahu and it was also the shortest when it grew out of sea level. It was about 3,000 ft.
Activity from Kaûena began roughly 5 million years ago. Despite being Oûahu's oldest volcano, it broke sea level 400,000 years after the Waiûanae did. This is due to Kaûena being built on a lower sea depth, whereas other Oûahu volcanoes were built on pre-existing ridges.
Around 3 million years ago, Kaûena, Waiûanae and Koûolau simultaneously emerged. Kaûena would later submerge below sea level at an unknown date.
In its current state, the crest of the Kaûena Ridge extends 35âÂÂ55 km wide and is located 75âÂÂ100 km northwest of Kaûena Point, the westernmost tip of Oûahu.
On May 22, 1956, a military plane flying to Oûahu reported brown pumice floating on the water and a smell of sulfur. One of the pilots reported it looked similar to volcanic eruption he had witnessed in the Philippines in 1952. Subsequent flights were flown out, and pilots reported yellow-colored water around Kaûena Ridge. Within days, brown pumice began washing up on the shores of Oûahu, and dead whales were reported around the area. A 1991 study found that lava had recently erupted in the area but couldn't determine the exact date, but it did state that an eruption in the 1900s could have occurred, or the volcanism may have occurred in the past 1,000 years. The most likely explanation for this event by scientists is a rejuvenation stage volcanic eruption. If this is the case it would be the only time that a rejuvenation stage eruption was witnessed by humans.