2015-2016 EL NINO-GENERATED OCEAN WAVE IMPACTS AND OTHER RECENT EROSIONAL CHANGES TO KUKUIHOOLUA ISLAND SEA ARCH AT LAIE, HAWAII, U.S.A

Kukuiho’olua Island is an islet that lies 164 meters due north of Laie Point, a peninsula of cemented, coastal, Pleistocene and Holocene sand dunes. Kukuiho’olua Island consists of the same dune deposits as Laie Point. The island is 173.75 meters in length, at its longest, with its eastern area having a width of 47 meters, which is the widest part, and a width of 27.5 meters on its western side. The island runs nearly due east-west, with a narrow, eroded, center that forms a sea arch that, prior to February 26, 2016 had a large boulder sitting inside of it – a large block that had fallen from the ceiling of the arch. The 2015-2016 El Niño was one of the strongest on record, resulting in anomalous wave heights across the Pacific. During the night of February 24-25, 2016, large storm waves, resulting from the unique El Niño conditions in the Pacific Ocean, washed the large boulder out from beneath the rock, significantly increasing the open area beneath it. Large waves also rose high enough for seawater to wash over Laie Point, causing significant erosion of its upper surface. Although it has not been previously documented, locals that live in Laie say that the sea arch formed during the 1 April 1946 tsunami – otherwise known as the April Fools’ Day Tsunami. The earliest known, surviving photograph of the island, taken in 1919 shows the island to be solid, with no sea arch present. A subsequent photo, taken in 1959 shows a very distinct arch with a large boulder lying beneath it, which lends credibility to the idea that the arch was created by the 1946 tsunami – despite the lack of a public record of being associated with the 1946 tsunami. In 1946, Laie was a remote, agricultural community. It was not until 1955 that a local university, the Brigham Young University-Hawaii campus, was founded. No detailed, geologic records were being kept in the area at the time of the 1946 tsunami. A comparison of photographs extending from 1959 to February 2016 shows little to no change in the structure and shape of the arch, despite another large tsunami that impacted Laie in 1957, and strong El Niño events in 1982-83 and 1997-98. This impact of the 1946 April Fools Day tsunami and the 2015-2016 El Niño waves on Kukuiho’olua Island and Laie Point are thus significant in the coastal history of Oahu’s North Shore region.