Hawaiian Hot Spots Not to Blame for Underwater Volcanoes

It turns out hot spots in Earth's mantle are not to blame for some of Hawaii's known underwater volcanoes, but rather they formed from cracks or fractures in the oceanic crust, according to a new study.

The discovery not only sheds light on the formation of this oceanic range, but also helps explain the famous bend in the Hawaiian-Emperor seamount chain, where the bottom half kinks at a 60-degree angle compared to the top half.

"There has been speculation among geoscientists for decades that some underwater volcanoes form because of fracturing," researcher Professor Dietmar Muller, from the University of Sydney, said in a statement. "But this is the first comprehensive analysis of the rocks that form in this setting that confirms their origins."

It is widely accepted among scientists that as Earth's plates move over fixed hot spots in its underlying mantle, it causes eruptions that create chains of now extinct underwater volcanoes, or "seamounts."

One of the most well known seamounts is the Hawaiian-Emperor chain in the northern Pacific Ocean. It is mostly composed of ocean island basalts - the type of lava that erupts above hot spots. But north of the Hawaiian chain, in a formation called the Musicians Ridge, researchers were surprised to find samples from seamounts that were not made up of the ocean island basalts.

"The oldest part of the Musicians Ridge formed approximately 90 million years ago from hot spots but these new samples are only about 50 million years old and have a different geochemistry," said Muller.

"They did not form because of a hot spot but because of plates cracking open at their weakest point, allowing new magma to rise to the seabed and restart the formation of underwater volcanoes," he explained. "They are near extinct hot spot volcanoes because that hot spot action millions of years earlier helped weaken the crust (the layer directly above the mantle) where new volcanoes now form." (Scroll to read on...)