Mauna Kea and Mauna Loa were created from different sources of lava, geophysicists conclude in a new report using isotopic analysis to "fingerprint" the plumes.
The same holds true for the massive volcanoes’ predecessors on Maui, Molokai, Oahu and Kauai, the scientists said.
The study is the first to conclusively relate geochemical differences in surface lava rocks from both chains to differences in their sources, 1,700 miles deep at the core-mantle boundary.
During the past 5 million years, Hawaiian volcanoes formed two parallel chains, one including Kilauea, Mauna Kea, Kohala, Haleakala and Molokai, and the other including Loihi (a submarine volcano off the coast of Kau), Mauna Loa, Hualalai, the seamount Mahukona, Kahoolawe, Lanai and Koolau on Oahu.
Each line has a distinct plumbing system, the researchers found using lava samples, including 120 new samples from Mauna Loa.
The scientists looked at radioactive isotopes of some exotic elements — rubidium, samarium and lutetium — as well as uranium-235 and thorium-232, which have a very long half-life and decay into isotopes of strontium, neodymium, hafnium and lead.
The daughter isotope ratios reflect the long-term history of the basalt-source reservoirs in the mantle, the researchers said.
"Hawaiian volcanoes are the best studied in the world and yet we are continuing to make fundamental discoveries about how they work," said co-author and University of Hawaii volcanologist Michael Garcia in a statement Tuesday.
The next step for the researchers will be to study the entire length of the Hawaiian chain as well as other key oceanic islands to determine if the two sources can be traced further back, possibly up to 42 million years ago.
The Hawaiian chain and the Emperor Seamounts to the northwest have been volcanically active for more than 80 million years.
The findings, published in the current issue of Nature Geoscience, come additionally from the University of British Columbia’s Pacific Centre for Isotopic and Geochemical Research and the University of Massachusetts.
