Geophysicists in Hawaii and Texas have come up with a mathematical model that could explain how Mauna Loa and Kilauea volcanoes are linked yet have distinct, separate eruptions.
The answer relates to how pressure waves behave below the Earth’s crust, 50 miles down, in a section of the upper mantle called the asthenosphere.
"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 Helge Gonnermann, an assistant professor of Earth science at Rice University in Houston.
Yet Kilauea and Mauna Loa must have separate channels to the source because their respective flows have slightly different chemical signatures.
Rarely do Hawaii’s two most active volcanoes erupt together — as most recently in 1984.
Far more often they have alternated: when one is active, the other is quiet. For instance, between 1934 and 1952, only Mauna Loa was active and between 1952 and 1974 only Kilauea was, according to the U.S. Geological Survey.
Yet between 2003 and 2007, global positioning system records showed they both bulged upward due to the pressure of rising magma.
"In the GPS records, we first see inflation at Kilauea and then about a half a year later at Mauna Loa," Gonnermann said in a statement Tuesday. "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."
In an email Wednesday, Gonnermann said magma rises to the surface from beneath each volcano from a partially molten region of the mantle, through what is called the brittle lithosphere, in likely long-lived and relatively well-connected pathways and cracks. He compared the lava system to an aquarium capped by brittle rock.
"If one were to pump water at one side into the bottom of the aquarium, the pressure would increase there first and then spread laterally throughout the aquarium," he said. "If there are multiple cracks in the overlying rock, water would squirt out first at the crack nearest to where water is added and last furthest from there. That water that squirts out is not the water that was added to the aquarium at that time. Rather, the water closest to the crack gets ‘pushed’ out by the increase in pressure that is transmitted from the inlet throughout the aquarium.
"In an aquarium filled with sand and water this will all happen very quickly. However, magma beneath Hawaii has the consistency (viscosity) of honey and as you may imagine it will take longer for pressure changes to be transmitted."
The results of the study, the first to model paired volcano interactions, is in the November issue of Nature Geoscience. The co-authors are UH geophysicists James Foster, Benjamin Brooks an Cecily Wolfe; and Michael Poland and Asta Miklius of the Hawaiian Volcano Observatory.
