A geological look at Hawaii shows that Oahu's mountains are dissolving from within due to groundwater. But will the Hawaiian Islands be around that long as tectonic plate movement suggests a tsunami could inundate the islands in the near future? Situated in the heart of the Pacific Ring of Fire, the Hawaiian Islands seem to be on borrowed time.
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O'ahu, or Oahu, known as "The Gathering Place", is the third largest of the Hawaiian Islands and the most populous of the islands in the U.S. state of Hawaii. The state capital, Honolulu, is on O'ahu's southeast coast. It is the 20th largest island in the United States. In the greatest dimension, this volcanic island is 44 miles (71 km) long and 30 miles (48 km) across. The length of the shoreline is 227 miles (365 km). The island is the result of two separate shield volcanoes: Wai'anae and Ko'olau, with a broad "valley" or saddle (the central O'ahu Plain) between them.
Hawaiian Islands Are Dissolving from Within, Study Says Science Daily - December 23, 2012
Most of us think of soil erosion as the primary force that levels mountains, however geologists have found that Oahu's mountains are dissolving from within due to groundwater. Someday, Oahu's Koolau and Waianae mountains will be reduced to nothing more than a flat, low-lying island like Midway. But erosion isn't the biggest culprit. Instead, scientists say, the mountains of Oahu are actually dissolving from within. The research pitted groundwater against stream water to see which removed more mineral material. According to the researchers' estimates, the net effect is that Oahu 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.
Hawaiian island is dissolving from within MSNBC - December 28, 2012
Plan your island getaway now: In time, the mountainous tropical paradise of Oahu will erode, according to new research, with the biggest losses coming from within the island itself. To be accurate, you do have some time to book that vacation before Hawaii's Oahu flattens from an island into a low-lying seamount. Researchers writing in the upcoming Feb. 15 issue of the journal Geochimica et Cosmochimica Acta estimate that the volcanic island will continue to grow, thanks to plate tectonics, for another 75,000 to 1.75 million years. After that, however, the forces working to eat away at Oahu from the inside out will begin to triumph.
Researchers at Brigham Young University in Utah investigated the forces that add and subtract material from Oahu. The island offers an ideal place to conduct such a study, the researchers said, as it consists of one kind of rock that is exposed to very different levels of precipitation. Various regions in Oahu can record between 2 and 23 feet of precipitation a year, depending on the local climate.
The researchers measured solids dissolved in both surface and groundwater from 45 streams and 30 springs and wells around the island, adding those new measurements to previously reported data, for a total of 170 water samples scattered across Oahu. Using that data, scientists calculated the mass Oahu loses each year. Although one might expect rain to carry away most of the soil in such a wet climate, underground freshwater springs actually removed the bulk of the mineral material from Oahu, the researchers found. "More material is dissolving from those islands than what is being carried off through erosion," study researcher Steve Nelson, a Brigham Young University geologist, said in a statement. In fact, groundwater carried between three and 12 times as much dissolved solids compared to surface water, the researchers report.
Oahu is made up of the remnants of two collapsed shield volcanoes, the kind known for burping out thick, oozy lava that hardens into new land. One volcano, Waianae, was active from about 4 to 2.6 million years ago; the other, Koolau, developed later.
Today, Oahu grows not because of volcanism, but from geologic uplift. As the younger Hawaiian Islands push the Pacific tectonic plate downward, nearby Oahu "pops up," as if on a seesaw. That uplift pushes Oahu's landforms upward at a rate of 0.2 feet per thousand years, enough (for now) to compensate for the losses caused by groundwater carrying away the island's mass. Researchers hope that the same methods they used on Oahu can help clarify how other tropical islands change in response to different climate conditions.
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