Recent mapping of the seafloor along with gravity and geochemical analyses of seafloor volcanic rocks off the Island of Oahu suggests that there may be a volcano along the submarine Kaena Ridge. If validated, the newly discovery edifice would provide fundamental new information about Hawaiian magmatic activity and its evolution in time. It will also help in the interpretation of geophysical data of the overlapping volcanic edifices that make up the Hawaiian Island chain. The project pursues this new discovery by returning to the area with a student/faculty-run oceanographic cruise that uses a remotely operated vehicle to collect more gravity data and spot-sample volcanic rocks from critical locations on the seafloor. Samples returned to the lab will be analyzed for major and trace elements and key radiogenic isotopes (Nd, Sr, Pb). Samples will be dated using K-Ar and Ar-Ar methods. Broader impacts of the work include international collaboration with French scientists and strong integration of research and education for students. In this project, students are engaged at all levels from project planning to participating in an oceanographic cruise, to carrying out the geochemical work, to making presentations at national meetings.
New bottom observations and the geochemistry of samples from the submarine region northwest of Oahu, Hawai‘i indicate that the island of Oahu is actually built from three major shield volcanoes, and not two, as previously thought. The oldest volcano occurs in the region of the submarine Kaena Ridge and has been called Kaena Volcano. Determination of the location and orientations of rift zones and other aspects of volcano structure, and geophysical observations that indicate where magma was concentrated in the volcano indicate an independent volcanic structure in the off-shore region, that cannot be related to volcanoes on the island of Oahu. The geochemical composition of rocks from this region have been used to characterize the melting and magmatic evolution processes that fed volcanic eruptions in this area. Most of the new geochemical data were collected by undergraduate and graduate students at the University of Hawaii. A range of geochemical parameters indicate that these processes are distinct from those for the other volcanoes on Oahu. Thus all the available new data indicate an older, precursor volcano to the island of Oahu. Because Kaena Volcano formed in isolation, far from any preexisting volcanoes, most of its volcanic output remained submerged beneath the sea. However, late in its history Kaena emerged above sea level, eventually reaching a height ~1000 m above present sea level. This new work has important implications for scenarios for volcanic growth and evolution, as well as for the composition and age of volcanic activity along the world’s best-studied hotspot chain. Most Hawaiian volcanoes form on the flanks of preexisting ones. Kaena might be the best example, and certainly the best exposed, of a Hawaiian volcano that formed in isolation and spent most of its history beneath sea level.
