10 December 2001

SAN FRANCISCO— From March to May this spring, MBARI’s research vessel Western Flyer and remotely operated vehicle Tiburon conducted an ambitious expedition to Hawaii. Results from the mostly geologic investigations will be presented this week at the American Geophysical Union Fall Meeting in San Francisco, California.

During the expedition, ROV Tiburon completed 57 dives ranging from 150 meters to 3,820 meters depth at various locations. MBARI scientists focused their efforts on four research themes around the islands: volcanic processes, deep flank structure of the islands, drowned shorelines, and submarine canyon processes. High-resolution base maps of the region collected by MBARI in 1998 were critical in targeting the studies.

David Clague, lead scientist of the expedition and geologist at MBARI, said, "Our high-resolution bathymetric maps revealed a collection of interesting seafloor features. With Tiburon and the base maps, we were able, for the first time, to image these seafloor features and to collect very targeted samples."

In one surprising finding, the video and samples collected by Clague and his colleagues suggest that submarine volcanoes can erupt explosively, even in deep water, and that the processes may be more similar to volcanoes on land. For example, layers of ash seen at 1,500 meters depth, such as those seen off Kauai, are evidence of explosive eruptions.

MBARI’s high-resolution bathymetry of Hawaii first revealed the presence of numerous flat-topped volcanoes on the seafloor around the islands. Clague and his colleagues had theorized that these "pancake" volcanoes—imagine the aspect ratio of a U.S. nickel—were created as continuously overflowing lava ponds rather than from erosion of taller structures. The video images from Tiburon captured evidence of this process to support this new theory.

"We’ve learned more about submarine volcanic processes in Hawaii in the last three years than was known in the previous 60 years," said Clague.

The recent Tiburon dives also allowed researchers to image submerged coral reefs, markers for the former shoreline of the island. The Hawaiian islands sink into the ocean at a measurable rate as they move off the hot spot that provides the magma to make them. The Tiburon images revealed ancient coral reefs that were partially dissolved when sea level fell faster than the island subsided. Future studies of the samples collected will be focused on how these reefs can be indicators of past climate change.

Other researchers involved in the expedition will present results from their studies of submarine canyon processes, plunge pools, and heat flow around the islands. The large size of seafloor features, high activity of volcanism, and rapid rates of subsidence make the Hawaiian islands an ideal place to study geologic processes.