Scientists chart
ancient mega-MauiThe four islands were joined
as a large land mass for
most of the last million years
About 1.2 million years ago, Maui, Molokai, Lanai and Kahoolawe were part of one huge land mass, about 30 percent to 40 percent larger than the Big Island.
Now scientists have put together a picture of what this land mass -- known as Maui Nui, or "big Maui" -- might have looked like and how the islands we know today came about.
Jonathan Price, of the Smithsonian Institution Museum of Natural History, and Deborah Elliott-Fisk, of the University of California at Davis, developed the computer images of Maui Nui using modern techniques to examine the effects of global sea-level change, age of volcanism and likely rates of volcano subsidence or sinking.
"They've sort of taken this thing back over a million years to when the various islands were growing and tried to look at what the large mass, Maui Nui, may have looked like at various times," said John Sinton, University of Hawaii geologist-geophysicist.
Price, in a telephone interview, said, "Definitely, a surprising feature was that it was considerably bigger than the Big Island."
That had been suggested, but the rate at which it shrank and split up was never clear, he said.
The major point, Price said, is that Maui Nui was a single land mass for about 75 percent of the last million years.
The concept that all four islands were once connected was first proposed 60 years ago by geologist Harold Stearns based on geologic evidence, and it has been well studied.However, Warren Wagner, Museum of Natural History curator of Pacific biology, said he was startled when he saw from the model that Maui Nui was "actually a big structure" and continued that way much longer than anyone thought.
Sinton, who reviewed a paper on the study by Price and Elliott-Fisk for publication in the journal Pacific Science, said they used good data on ocean depth and topography, "plus they've accounted for subsidence of the islands, which has never been done quantitatively before."
Price, a biogeographer interested in factors that help to shape biodiversity, such as geologic and climate history, said, "In Hawaii, more than just about anywhere you can imagine, the distribution of species and what species you find here are really a function of the history of the islands."
Price said Maui Nui had "an interesting array of environments in the past. ... What we look at today as discrete islands is really not the whole picture."
Maui Nui had extensive lowlands, dotted with upland areas, which permitted easy dispersal of plants and animals, according to the model."Even flightless or slowly dispersing species could spread widely, making the biologic communities on these islands more similar than might be expected for islands always isolated from each other," Price and Elliott-Fisk wrote.
Chances also were greater that species traveling by air or water could land on the ancient land mass, they said.
"Once there, those species had a wealth of environments in which to evolve. Thus Maui Nui provided a rich storehouse for subsequent colonization by plants and animals on the island of Hawaii, the youngest island in the chain."
Providing evidence that the four islands were once a single island were flightless ibises found on Molokai and Lanai and one type of flightless duck found on Molokai, Maui and Oahu, Price said.
"There was a brief connection between Oahu and the younger volcanoes that make up Maui Nui more like 2 million years ago. It didn't last very long. But the fact that you have this type of flightless duck on Oahu and also on Maui Nui suggests it managed to walk all the way across."
Maui Nui included Penguin Bank, a shoal west of Molokai that began as a shield volcano and finished its building stage when it was connected to Oahu, the study showed.
Now lying under a thick coral cap, the Penguin Bank volcano once covered an area eight times that of Kahoolawe today.
"Using Price's model, we can watch the response of Maui Nui to subsidence and sea level change as we move the clock forward or back," the Hawaiian Volcano Observatory reported on the study.
"Hawaii's volcanoes build by a vast outpouring of lava from the earth's upper mantle. The oceanic crust bows under the added weight, subsiding at rates exceeding 0.1 inch per year," the scientists wrote.
"As Maui Nui's upbuilding volcanoes waned, the saddles between them were submerged, isolating the different volcanoes as distinct islands."
Sea level changes also contributed to separation of the islands, either shrinking or enlarging them. The last low sea stand was only about 20,000 years ago, Price said, but the sea level is higher now than at almost any time in 200,000 years because of melting glaciers.
The first connection broken was between Penguin Bank and West Molokai volcanoes, according to the model. "A permanent embayment separated East Molokai from West Maui by about 700,000 years ago, but these two volcanoes remained connected via Lanai.
"The saddle between East Molokai and Lanai submerged about 600,000 years ago, then re-emerged whenever glaciers grew and sea level fell."
The Kahoolawe-Maui connection disappeared between 200,000 and 150,000 years ago, but Maui, Lanai and Molokai remained together intermittently until as recently as about 18,000 years ago, the model shows.
As sea level rose, Molokai became isolated, and the land bridging Lanai and Maui was submerged, creating the four islands.
UH geologist-geophysicist Michael Garcia said Price's model provides a framework to try to fine-tune the concept of Maui Nui.
But he said, "One thing that is not clear is trying to integrate the notion that the islands sink at different rates, and they may actually rise, as Chip Fletcher (UH geologist-geophysicist) has suggested for Oahu."
Sea level changes resulting from growth and melting of continental glaciers is pretty well known, Garcia said, "but sinking of the islands is a more complicated issue that we don't fully understand."