Woods Hole Oceanographic Institution

Rambling and rumbling on an island volcano
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Lush tropical forests on the Samoan island of Ta'u. (Photo by Rhea Workman, WHOI)
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GPS locations on Ta'u Island, Samoa.
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WHOI graduate student Rhea Workman explains her work on Volcanism to students on Ta'u. (Photo by Stan Hart)

The Samoan island of Ta’u is a tropical paradise, but Rhea Workman knows it was created by an undersea volcano that is still active. Ta’u’s central volcano was formerly dome-shaped, but one of its sides collapsed in landslides that cast debris all the way onto the seafloor. The landslides left a steep escarpment, which is primed for further catastrophic landslides—and possibly tsunamis—especially if it is disturbed by movements inside the volcano.

Within a volcano’s underlying magma chamber, magma or gas continually surges or subsides, inflating, deflating, and deforming the volcano’s surface. These deformations are usually tiny, but they can be measured to evaluate what’s going on inside the volcano and predict whether it might erupt.

Workman, a graduate student in the WHOI Geology and Geophysics Department, wanted to assess Ta’u’s volcano and landslide hazard potential by measuring the volcano’s subtle motions with Global Positioning Satellite receivers, which can measure ground-motion changes within 1 centimeter. She organized an expedition, conscripting GPS equipment and fellow MIT/WHOI Joint Program students. In 2002, they installed GPS benchmarks (middle image) throughout the island and took GPS measurements. In 2004, Workman returned to re-measure the benchmarks, also taking time to explain her research at local schools (bottom image).

Since her return, Workman scrambled to complete and defend her Ph.D. dissertation on March 16. Dr. Workman will now analyze and compare her GPS measurements to see if she can detect telltale ground motion on Ta’u.

This research was supported by a grant from the Robert H. Cole Endowed Ocean Ventures Fund.

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