Even an area so studied as Hawaii sometimes yields surprises – a recent study conducted by researchers at the University of Hawaiʻi at Mānoa School of Ocean and Earth Science and Technology (SOEST) and the University of Rhode Island (URI) changes the very foundation of how the Hawaii islands were formed: it is the eruptions of lava on the surface, extrusion, which grow Hawaiian volcanoes, rather than internal emplacement of magma, as was previously thought.

3-D view of topography & seafloor relief of Hawaiian Islands; colors show residual gravity anomaly - red shows higher densities, blue shows lower densities.

3-D view of topography & seafloor relief of Hawaiian Islands; colors show residual gravity anomaly – red shows higher densities, blue shows lower densities.

Before this, the currently accepted theory was that Hawaiian volcanoes grew primarily internally – magma intrudes and solidifies before it hits the surface. While this type of growth does occur, it is definitely not the major component of the growth; previous studies which concluded otherwise were based on observations over a very small time frame.

“The discrepancy we see between our estimate and these past estimates emphasizes that the short-term processes we currently see in Hawaiʻi (which tend to be more intrusive) do not represent the predominant character of their volcanic activity,” said Ashton Flinders, study author.

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Ashton Flinders (M.S. from UHM), lead author and graduate student at URI worked with his colleagues and Jim Kauhikaua of the U.S. Geological Survey – Hawaiʻi Volcano Observatory to compile historical land-based gravity surveys as well as marine surveys from the National Geophysical Data Center and from the UH R/V Kilo Moana. These data provide an insight over longer periods of time.

This could have a significant impact on how the island develops and what kind of challenges it has to face in the future.

“This could imply that over the long-term, Kilauea’s ERZ will see less seismic activity and more eruptive activity that previously thought. The 3-decade-old eruption along Kilauea’s ERZ [east rift zone] could last for many, many more decades to come,” said Dr. Garrett Ito, Professor of Geology and Geophysics at UHM and co-author.

“I think one of the more interesting possible implications is how the intrusive-to-extrusive ratio impacts the stability of the volcano’s flank. Collapses occur over a range of scales from as large as the whole flank of a volcano, to bench collapses on the south coast of Big Island, to small rock falls,” said Flinders. Intrusive magma is more dense and structurally stronger than lava flows. “If the bulk of the islands are made from these weak extrusive flows then this would account for some of the collapses that have been documented, but this is mainly just speculation as of now.”

They are now working on a new density model which will serve as a starting point for future studies and pave the way for a better understanding of the entire volcanic system.

Via University of Hawai’i at Manoa.