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Middle age spread. More than one person moving through their 40s and 50s has been known to complain about getting old and heavier at the same time. But it now appears that volcanoes may also get old and fat together as well.
University of Cincinnati geology graduate student Keri Craven headed to Hawaii this September to test that theory.
The volcanoes that formed the island chain are known to go through four distinct stages, and because you can find volcanoes in every stage of development there, it makes a perfect test site.
Craven is focusing her work on the transition between two of the four stages.
"They gain weight with age," Craven explained. "As the lava flows out, the weight of the island builds very fast."
That much is certain. What isn't certain is whether the weight change drives the aging process or the switch from rocks known as tholeiitic to the Phase 3 alkalic rocks.
"Because it's so massive, it's putting a lot more pressure on the magma chamber underneath." That might be enough pressure to cause the minerals in the lava to crystallize and settle out, causing lavas to erupt in the new form. An alternative theory says the change is caused on partial melting of different rock and mineral sources in the mantle.
"Both models could actually be correct," she noted. "They could go hand in hand, or they could be working independently of each other."
An important factor to keep in mind is the movement of the Earth's crust. As it moves, the growing volcano will be moving over the magma plume that feeds it. So the weight above the magma chamber will change with time. Craven believes that's an important factor in how Hawaiian volcanoes age. To test the models, Craven climbed over old lava flows on southwestern Maui collecting samples from Phase 3 and Phase 4 alkalic rocks.
When she returned to the lab at the University of Cincinnati, the rocks will be analyzed chemically so Keri can determine the temperature and pressure conditions that could have formed those rocks.
That will help answer the question of whether it was the weight of the volcano on top of the magma chamber or other factors that pushed the volcano from Phase 2 to Phase 3.
More weight equals more pressure, and Craven uses a special computer program and various calculations to see if the volcano's weight produced sufficient pressure to produce Phase 3 rocks.
She was assisted in her research by UC geology alumna Tammie Gerke and geology undergraduate Lisa Fay. Craven will present her results later this year at the annual meeting of the Geological Society of America in Denver.
Craven is studying under UC geology department head Attila Kilinc who recently led a special course on volcanoes in Hawaii this year.