Staff from the USGS Pacific Coastal and Marine Science Center Marine Facility engineered a Free Ascent Tripod (FAT) for deployment in deep-sea environments along the Cascadia Subduction Zone. This tripod will provide scientists a prolonged, up-close look at the seabed, measuring processes such as sediment transport thousands of feet beneath the surface.
USGS-Engineered Tripod Allows Study of Deep-Sea Oceanographic Processes
The tripod is equipped with instruments that measure deep-sea currents, turbidity, salinity, and other parameters. These data will be used to better characterize the causes of turbidity flows—rapid, sediment-laden currents moving downslope—that carry sediment from the continental shelf to the deep sea. Earthquakes are a known trigger for turbidity flows along tectonically active margins, but other causes, such as high-energy storms, can potentially send large sediment pulses cascading offshore to the deep sea, as well.
“What is unique about the FAT is that it will be deployed much deeper than most other oceanographic tripods, which are generally restricted to the continental shelf,” said USGS Research Geologist Jenna Hill, who helped design the tripod. “Moorings are much more frequently used in deeper water, but they have several disadvantages, namely that all the instruments are mounted on one vertical line. The FAT allows us to have instruments mounted about a meter above the seabed to look specifically at processes there, such as bottom currents that move sediment around.”
Scientists at the USGS and University of Washington are working together to understand the differences between earthquake-triggered and oceanographically triggered turbidity flows, which allows them to better interpret the geologic record of past events and improve the potential for future hazard predictions.
USGS performed a test build-out and deployment of the FAT off the Santa Cruz Wharf in late February 2023. The real deployment will be far offshore of the Columbia River Mouth, in Astoria Canyon, in March 2023.
The FAT will be lowered from a research vessel to a depth of 1,500 meters (4,921 feet), where it will settle on the Astoria Canyon bottom and collect data continuously for 12 months. When the research vessel returns next spring, the tripod’s floatation system will be activated, and a beacon conveying its position to the research vessel allows the tripod to be retrieved.