3D view of topography and seafloor relief of Hawaiian Islands (colors show residual gravity anomaly)

A recent study by researchers at the University of Hawaiʻi at Mānoa School of Ocean and Earth Science and Technology and the University of Rhode Island changes the understanding of how the Hawaiian Islands formed. Scientists have determined that it is the eruptions of lava on the surface, extrusion, which grow Hawaiian volcanoes, rather than internal emplacement of magma, as was previously thought.

The study, “Intrusive dike complexes, cumulate cores, and the extrusive growth of Hawaiian volcanoes” was published in Geophysical Research Letters. Study authors are University of Rhode Island’s Ashton Flinders, UH Mānoa’s Garrett Ito, Michael O. Garcia, John M. Sinton and Brian Taylor and U.S. Geological Survey’s Jim Kauhikaua

Before this work, most scientists thought that Hawaiian volcanoes grew primarily internally—by magma intruding into rock and solidifying before it reaches the surface. While this type of growth does occur, along Kīlauea’s East Rift Zone, for example, it does not appear to be representative of the overall history of how the Hawaiian Islands formed. Previous estimates of the internal-to-extrusive ratios (internally emplaced magma versus extrusive lava flow) were based on observations over a very short time frame, in the geologic sense.

The researchers compiled historical land-based gravity surveys with more recent surveys on the Big Island and Kauaʻi, along with marine surveys from the National Geophysical Data Center and from the University of Hawaiʻi at Mānoa’s R/V Kilo Moana. These types of data sets allow scientists to infer processes that have taken place over longer time periods.

“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 lead author Flinders.

“This could imply that over the longterm, Kilauea’s East Rift Zone will see less seismic activity and more eruptive activity than previously thought. The three-decade-old eruption along Kilauea’s East Rift Zone could last for many, many more decades to come,” said Ito, professor of geology and geophysics at UH Mānoa.

“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.”

The authors, hope this new density model can be used as a starting point for further crustal studies in the Hawaiian Islands.

A UH Mānoa news release