Scientists have discovered that mountains on the Hawaiian island of Oahu are dissolving from within.Oahu, the third largest of the Hawaiian islands, is well known for its two shield volcanoes: Waiʻanae and Koʻolau. Measurements of minerals loss taken from their ground water and surface run-off allowed the scientists to work out how much is lost from the mountains each year. The team’s findings suggest that this mountainous island could one day be as flat as the low-lying Midway Island, another part of the Hawaiian archipelago.
"We tried to figure out how fast the island is going away and what the influence of climate is on that rate," says geologist Steve Nelson from Brigham Young University.
Their surprising discovery was that both Waiʻanae and Koʻolau are actually shrinking from within, rather than by the usual loss from erosion.
"More material is dissolving from those islands than what is being carried off through erosion," says Nelson.
However, it’s not likely that the mountains will be disappearing any time soon. The scientists estimate this shrinking will be off-set by the island rising as it is pushed north-west by plate tectonics. The dissolving effect will eventually triumph, but not for another 1.5 million years.
The team made their calculations based on the difference between minerals lost through ground water, the dissolving effect, and those lost through weathering and erosion, seen in the surface run-off. Their discovery that greatest loss was in the groundwater rather than the surface run-off indicates that Waiʻanae and Koʻolau are disappearing from within. They hope their findings will shed further light on how climate change may affect Hawaii in the future.
"All of the Hawaiian Islands are made of just one kind of rock," says Nelson.
"The weathering rates are variable, too, because rainfall is so variable, so it’s a great natural laboratory."
The study is published in the journal Geochimica et Cosmochimica Acta.