Hawaii’s two most active volcanoes, Maunaloa and Kilauea, are only 21 miles apart. Because of their proximity, people have long wondered whether they are connected beneath the surface of the Earth and how a connection might affect their eruptions.   

New research from scientists at the University of Hawaii at Manoa, which was published in the Journal of Petrology last month, indicates the two shield volcanoes share a magma source within Hawaii’s hotspot, also known as the mantle plume. They also have their own magma sources within the mantle plume. 

Sometimes the magma from the shared portion of the mantle plume travels up to Kilauea, while at other times it travels up to Maunaloa. The volcano receiving magma from this shared area is more likely to be active, while the other “becomes sleepy,” according to Aaron Pietruszka, the lead researcher on the study and an associate professor at UH Manoa. 

However, Pietruszka added, this is a broad pattern, and it is possible for both volcanoes to erupt at the same time, since they also have their own sources of magma. “Each volcano gets a boost of extra magma from the mantle from time to time. And then when that happens, its activity increases from its baseline.”

Melt (aka magma) is generated within the Hawaiian mantle plume (asthenosphere). Each volcano taps melt from their respective end-member sources. A third, compositionally distinct mantle source — the shared component — is likely between these volcanoes. Melt from the shared mantle source is diverted alternately to Maunaloa (a) or Kilauea (b) on a timescale of decades. (Figure courtesy of Journal of Petrology/Aaron Pietruszka)

For this research, Pietruszka studied the chemical composition of lava that came from Maunaloa and Kilauea eruptions over the past 200 years. 

“The magma coming up beneath Kilauea and Mauna Loa is typically different from each other,” said Pietruszka. “They're broadly similar, but there are very easy to measure differences in chemistry between the two volcanos, and those compositional signatures change over time, and that's what we're tracking.” 

The magma that rises from the mantle takes decades to make its way to the Earth’s surface, so Pietruszka said his research won’t tell us about eruptive activity within the next few years, but can be useful when wondering what might happen over a longer timescale. 

Since 2010, Pietruszka’s team has noticed changes in the chemical composition of lava from Kilauea, which indicates it is receiving less and less magma from the shared area in the mantle plume. Instead, the magma from the shared area in the mantle plume is heading to Maunaloa.

“My prediction is that over the next decades, like 10, 20, 50 years, if the chemical changes continue, we would expect to see Kilauea activity slow down a little bit, and Maunloa’s activity to pick up,” said Pietruszka. 

Michelle Broder Van Dyke covers the Hawaiian Islands for Spectrum News Hawaii. Email her at michelle.brodervandyke@charter.com.