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...)
Vulnerable spots in Earth's plates crack when they are stressed. In this case, cracking resulted from the movement of the Pacific Plate roughly 50 million years ago. It likely started to dive or submerge back into Earth's crust at its northern and western edges, forming the younger seamounts.
"We believe tectonic changes along the margins of the Pacific Plate around 50 million years ago put the weakest points of the Pacific Ocean crust under tension and created the youngest Musicians Ridge seamounts," Muller added.
These findings also provide a possible explanation for the unique bend in the Hawaiian-Emperor chain.
"It also caused the flow in the slowly convecting mantle under the Pacific to change dramatically, to the point that the Hawaiian hot spot in Earth's mantle changed its position," the researcher explained. "The resulting seamounts along the Hawaii-Emperor chain changed their position accordingly and the bend was born."
While such underwater volcanoes are fascinating, they are also a concern to scientists. Nature World News recently reported that underwater volcano flare-ups could affect climate change. Although these volcanoes are normally non-volatile, changes in the Earth's orbit and sea levels could cause more frequent flare-ups, or pulses. This would release so much carbon dioxide into the atmosphere that it could shift planetary temperatures.
"People have ignored seafloor volcanoes on the idea that their influence is small - but that's because they are assumed to be in a steady state, which they're not," marine geophysicist Maya Tolstoy, who led the research, said in a statement. "They respond to both very large forces, and to very small ones, and that tells us that we need to look at them much more closely."
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