Soil erosion is often considered to be the primary cause of land and mountain loss on islands, but new research has found that on Oahu the mountains are being dissolved and destroyed by groundwater.
Eventually the mountains Koolau and Waianae on Oahu will be dissolved until the island becomes a nearly flat, very low-lying island similar to Midway.
“We tried to figure out how fast the island is going away and what the influence of climate is on that rate,” said Brigham Young University geologist Steve Nelson. “More material is dissolving from those islands than what is being carried off through erosion.”
The research was done by comparing the effects of groundwater compared to stream water, to find out which one was removing more mineral material. “Nelson and his BYU colleagues spent two months sampling both types of sources. In addition, ground and surface water estimates from the U.S. Geological Survey 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 said. “The weathering rates are variable, too, because rainfall is so variable, so it’s a great natural laboratory.”
In order to get an idea of what will happen to the island in the future it was also necessary to take into account plate tectonics. As Oahu is being forced northwest, it actually rises in elevation slowly.
“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.”
The researchers got something of a surprise when they were doing their mineralogical analysis of the soil samples that they took.
“The main thing that surprised me on the way was the appearance of a large amount of quartz in a saprolite taken from a 1-meter depth,” Brian Selck, co-author of the study, said.
The research was just published in the journal Geochimica et Cosmochimica Acta.
Source: Brigham Young University
Image Credits: Brigham Young University
For the fate of the sons of men and the fate of beasts is the same; as one dies, so dies the other. They all have the same breath, and man has no advantage over the beasts; for all is vanity. - Ecclesiastes 3:19