A study has changed a conception of how the Hawaiian Islands formed, researchers say, with a new model of the most common volcanic activity in the island chain. Researchers from the University of Hawaii and the University of Rhode Island say they\'ve determined it\'s eruptions of lava on the surface -- a process known as extrusion -- that grow Hawaiian volcanoes, rather than internal emplacement of magma as was previously thought. It had long been believed Hawaiian volcanoes grew primarily internally -- from magma intruding into rock and solidifying before it reaches the surface -- but that process does not appear to be representative of the overall history of how the Hawaiian Islands formed, the researchers said. Previous estimates of the internal-to-extrusive ratios -- internally emplaced magma versus extrusive lava flow -- were based on observations over a very short time frame in the geologic scheme of things, they said. Historical land-based gravity surveys with more recent surveys on the Big Island of Hawaii and Kauai, along with marine surveys, allow them to infer processes that have taken place over longer time periods, the researchers said. \"The discrepancy we see between our [study] estimate and these past estimates emphasizes that the short term processes we currently see in Hawaii (which tend to be more intrusive) do not represent the predominant character of their volcanic activity,\" researcher Ashton Flinders said.