New research has revealed that in addition to the well known forces of soil erosion, the Hawaiian Islands are experiencing significant erosion due to the groundwater under the islands working to dissolve the island from within. Specifically, the mountains on Oahu will eventually be completely leveled and end up as flat as Midway Island.
The effect that groundwater is having, dissolving the rock that makes up the Hawaiian Islands, is actually more significant than the forces of soil erosion.
“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 pitted groundwater against stream water to see which removed 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.”
The future of the islands is also going to be influenced significantly by plate tectonics. Oahu is currently being slowly pushed northwest, and as it is the mountains are being pushed upwards somewhat.
“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.”
“Undergraduate student Brian Selck co-authored the study, which appears in the journal Geochimica et Cosmochimica Acta. Unfortunately for him, he joined the project only after the field work in Hawaii took place.”
“Instead, Selck performed the mineralogical analysis of soil samples in the lab back in Provo. The island’s volcanic soil contained at least one surprise in weathered rock called saprolites.”
“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,” Selck said.
“After he graduates from BYU, Selck will pursue a career in hydrogeology. BYU geology professor David Tingey joins Nelson and Selck as a co-author on the new study.”
Here’s some more information on the formation and geology of the Hawaiian Islands:
“An archipelago situated some 2,000 mi southwest of the North American mainland, Hawaii is the southernmost state of the United States and the second westernmost state after Alaska. Only Hawaii and Alaska do not share a border with another U.S. state.”
“Hawaii is the only state of the United States that is not geographically located in North America, grows coffee, is completely surrounded by water, is entirely an archipelago, has royal palaces, and does not have a straight line in its state boundary.”
“Hawaii’s tallest mountain, Mauna Kea, stands at 13,796 ft but is taller than Mount Everest if followed to the base of the mountain, which, lying at the floor of the Pacific Ocean, rises about 33,500 ft.”
“The eight main islands, Hawaiʻi, Maui, Oʻahu, Kahoʻolawe, Lanaʻi, Molokaʻi, Kauaʻi and Niʻihau are accompanied by many others. Kaʻala is a small island near Niʻihau that is often overlooked. The Northwest Hawaiian Islands are a series of nine small, older masses northwest of Kauaʻi that extend from Nihoa to Kure that are remnants of once much larger volcanic mountains. There are also more than 100 small rocks and islets, such as Molokini, that are either volcanic, marine sedimentary or erosional in origin, totaling 130 or so across the archipelago.”
“The Hawaiian islands were (and continue to be) continuously formed from volcanic activity initiated at an undersea magma source called a hotspot. As the tectonic plate beneath much of the Pacific Ocean moves to the northwest, the hot spot remains stationary, slowly creating new volcanoes. Due to the hotspot’s location, the only active volcanoes are located around the southern half of the Big Island. The newest volcano, Lōʻihi Seamount, is located south of the Big Island’s coast.”
“The last volcanic eruption outside the Big Island occurred at Haleakalā on Maui before the late 18th century, though it could have been hundreds of years earlier. In 1790, Kīlauea exploded with the deadliest eruption (of the modern era) known to have occurred in what is now the United States. As many as 5,405 warriors and their families marching on Kīlauea were killed by that eruption.”
“Volcanic activity and subsequent erosion have created impressive geological features. The Big Island has the third highest point among the world’s islands.”
“Slope instability of the volcanoes has generated damaging earthquakes with related tsunamis, particularly in 1868 and 1975. Steep cliffs have been caused by catastrophic debris avalanches on the submerged flanks of ocean island volcanos.”
Image Credits: Brigham Young University; Lava via Wikimedia Commons