Construction of submarine volcanic rift zones in Hawai`i

Jennifer R. Reynolds, Ph.D.
Monterey Bay Aquarium Research Institute

Wednesday, April 7, 1999
3:00 p.m.—Pacific Forum

Six submarine Hawaiian rift zones were surveyed during MBARI's mapping program in 1998, using a new 30 kHz EM300 multibeam sonar. The rift zones range in length and age from the young 11 km North Rift and 20 km South Rift of Loihi Seamount to the mature, 130 km East Rift Zone/Puna Ridge on Kilauea, to extinct rift zones of Mahukona, Hilo Ridge (Kohala), and Hana Ridge (Haleakala). The bathymetric maps show a variation in the size and shape of monogenetic volcanic cones that suggest an evolutionary progression in eruption characteristics along a rift zone during the life of the volcano. These changes are consequences of lengthening of the rift zone and long-term waxing and waning of the magma supply. Major structural features are also revealed. For example, on Puna Ridge, there is evidence for major rotational block faulting of the south flank, related to rift spreading. From maps of landslide scarps on Loihi, Hilo, and Hana Ridges, it is evident that the landslides occurred while the rifts were volcanically active, and that they caused shifts in the position and orientation of each rift axis.

Puna Ridge, the submarine extension of Kilauea's East Rift Zone, was the target of a surveying and sampling expedition in October 1998. We collected DSL-120 side-scan sonar, ARGO-II seafloor photography, near-bottom magnetics, and rock samples from 77 locations. Preliminary cruise results and implications for the overall structure and magmatism of the rift zone will also be presented.

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