Oahu – the third largest of the Hawaiian Islands – will be reduced to nothing more than a flat island, someday, according to a research led by Brigham Young University geologist Steve Nelson.
“We tried to figure out how fast the island is going away and what the influence of climate is on that rate. More material is dissolving from those islands than what is being carried off through erosion,” said Nelson.
The findings, published in the journal Geochimica et Cosmochimica Acta, show that the Koolau and Waianae mountains of Oahu are dissolving from within.
The study pitted groundwater against stream water to see which removed more mineral material. Nelson and his colleagues spent two months sampling both types of sources. In addition, ground and surface water estimates helped them calculate the total quantity of mass that disappeared from the island each year.
“All of the Hawaiian Islands are made of just one kind of rock,” Nelson explained. “The weathering rates are variable, too, because rainfall is so variable, so it’s a great natural laboratory.”
Forecasting the Oahu’s future also needs to account for plate tectonics. As the island is pushed northwest, it actually rises in elevation at a slow but steady rate. You’ve heard of mountain climbing; this is a mountain that climbs.
The island will continue to grow for as long as 1.5 million years. Beyond that, the force of groundwater will eventually triumph and the island will begin its descent to a low-lying topography.
Bibliographic information: Nelson ST et al. 2013. The denudation of ocean islands by ground and surface waters: The effects of climate, soil thickness, and water contact times on Oahu, Hawaii. Geochimica et Cosmochimica Acta, vol. 103, pp. 276–294