A Geologic Survey Of The Near-Shore Regions Around White Island, New Zealand; Sidescan Imagery, Rock And Gas Samples From The 1995 MMTC-WIS Survey.

In 1995 the Marine Minerals Technology Center (MMTC) of the University of Hawaii conducted a sidescan sonar survey and sampling expedition of the submarine geology and hydrothermal systems surrounding the active volcano White Island. The island is located in the Bay of Plenty, within the geothermally active Taupo Volcanic Zone off-shore of the North Island of New Zealand, and is the site of numerous shallow-water hydrothermal systems. The survey system, an EdgeTech DF1000 sonar, was a dual frequency 100 kHz & 500 kHz sonar capable of imaging the seafloor at better than 1 m resolution and possibly detecting gas bubbles within the water column. Sidescan imagery clearly shows sand channels, debris slumps, submarine landslides, and volcanic ridges all around the island to roughly 800 meters offshore. However, analyses of the both raw and processed acoustic data indicate that the sonar was not able to image any of the shallow-water hydrothermal gas seeps known to exist around the island. Vents were located using a commercial fish finder and knowledge from local tour guides and divers. Eleven gas samples from three different sites were collected by divers for analysis of chemical and isotopic composition. Rock samples were collected from thirteen underwater outcrops for correlation with existing data on subarial island flows sampled by previous investigators. Thin sections and XRF analysis were done for each rock to determine mineral assemblages along with major and trace elements, which were used to tie submarine samples to specific subarial stratigraphic layers.