A new Rice University-led study finds that a deep connection about 50 miles underground can explain the enigmatic behavior of two of Earth's most notable volcanoes, Hawaii's Mauna Loa and Kilauea. The study, the first to model paired volcano interactions, explains how a link in Earth's upper mantle could account for Kilauea and Mauna Loa's competition for the same deep magma supply and their simultaneous "inflation," or bulging upward, during the past decade.

The study appears in the November issue of Nature Geoscience.

The research offers the first plausible model that can explain both the opposing long-term eruptive patterns at Mauna Loa and Kilauea - when one is active the other is quiet - as well as the episode in 2003-2007 when GPS records showed that each bulged notably due to the pressure of rising magma. The study was conducted by scientists at Rice University, the University of Hawaii, the U.S. Geological Survey (USGS) and the Carnegie Institution of Washington.

"We know both volcanoes are fed by the same hot spot, and over the past decade we've observed simultaneous inflation, which we interpret to be the consequence of increased pressure of the magma source that feeds them," said lead author Helge Gonnermann, assistant professor of Earth science at Rice University.

"We also know there are subtle chemical differences in the lava that each erupts, which means each has its own plumbing that draws magma from different locations of this deep source.

"In the GPS records, we first see inflation at Kilauea and then about a half a year later at Mauna Loa," he said.

"Our hypothesis is that the pressure is transmitted slowly through a partially molten and thereby porous region of the asthenosphere, which would account for the simultaneous inflation and the lag time in inflation.

Because changes in pore pressure are transmitted between both volcanoes at a faster rate than the rate of magma flow within the porous region, this can also explain how both volcanoes are dynamically coupled, while being supplied by different parts of the same source region."

Gonnermann said the transmission of pressure through the permeable rock in the asthenosphere is akin to the processes that cause water and oil to flow through permeable layers of rock in shallower regions of Earth's crust.

"When we fitted the deformation, which tells us how much a volcano inflates and deflates, and the lava eruption rate at Kilauea, we found that our model could simultaneously match the deformation signal recorded over on Mauna Loa," said James Foster, co-author and assistant researcher at the University of Hawaii School of Ocean and Earth Science and Technology.

"The model also required an increase in the magma supply rate to the deep system that matched very nicely with our interpretations and the increased magma supply suggested by the jump in CO2 emissions that occurred in late 2003."

Mauna Loa and Kilauea, Earth's largest and most active volcanoes, respectively, are located about 22 miles apart in the Hawaii Volcanoes National Park on the island of Hawaii.

They are among the planet's most-studied and best-instrumented volcanoes and have been actively monitored by scientists at USGS's Hawaiian Volcano Observatory (HVO) since 1912. Kilauea has erupted 48 times on HVO's watch, with a nearly continuous flank eruption since 1983. Mauna Loa has erupted 12 times in the same period, most recently in 1984.

"To continue this research, we submitted a proposal to the National Science Foundation (NSF) earlier this summer to extend our study back in time to cover the last 50 years," Foster said.

"We plan to refine the model to include further details of the magma transport within each volcano and also explore how some known prehistoric events and some hypothetical events at one volcano might impact the other. This work should help improve our understanding of volcanic activity of each volcano."

Gonnermann said there has been disagreement among Earth scientists about the potential links between adjacent volcanoes, and he is hopeful the new model could be useful in studying other volcanoes like those in Iceland or the Galapagos Islands.

"At this point it is unclear whether Hawaii is unique or whether similar volcano coupling may exist at other locations," Gonnermann said. "Given time and ongoing advances in volcano monitoring, we can test if similar coupling between adjacent volcanoes exists elsewhere."

Study co-authors include Michael Poland and Asta Miklius, both of HVO; Benjamin Brooks of the University of Hawaii; and Cecily Wolfe of the University of Hawaii and the Carnegie Institution of Washington.