The warm fluid flowing from the Oregon seafloor, coming from the Cascadia fault, could provide clues to earthquake hazards

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April 10, 2023

This sonar image of the Pythias Oasis site shows bubbles rising from the seafloor about two-thirds of a mile deep and 50 miles off Newport, Oregon. These bubbles are a by-product of a unique location where chemically distinct warm fluids gush from the sea floor. The researchers believe this fluid comes directly from the massive Cascadia region, or plate boundary, and helps control the buildup of stress between the two plates.

The field of plate tectonics is not that old, and scientists continue to learn the details of geological faults producing earthquakes. The Cascadia subduction zone – the eerily quiet sea fault that threatens to trigger a magnitude 9 earthquake in the Pacific Northwest – still holds many mysteries.

A study conducted by the University of Washington discovered leaks of a warm, chemically distinct fluid gushing from the sea floor about 50 miles from Newport, Oregon. The paper, published Jan. 25 in Science Advances, describes the unique underwater spring that the researchers have named the Pythia Oasis. Observations indicate that the source of the geyser is water 2.5 miles from the sea floor at plate boundaries, which regulates pressure on the marine fault.

The team made the discovery during a weather-related delay of a cruise aboard the RV Thomas G. Thompson. The ship’s sonar showed an unexpected plume of bubbles about three-quarters of a mile below the ocean’s surface. Further exploration using an underwater robot revealed that the bubbles were just a minor component of a warm, chemically distinct liquid gushing from seafloor sediments.

“They explored in that direction and what they saw wasn’t just methane bubbles, but water coming out of the sea floor like a firehose. This is something I’ve never seen before,” said co-author Evan Solomon, an associate professor of oceanography at the University of Washington who studies seafloor geology. To my knowledge, it has not been observed before.

This feature was discovered by first author Brendan Phillip, who did the work as a graduate student at the University of Washington and now works as a policy advisor in the White House.

Observations from subsequent sea voyages show that the liquid leaving the sea floor is 9 °C (16 °F) warmer than the surrounding seawater. Calculations indicate that the liquid comes directly from the Cascadia megathrust, with temperatures ranging from 150 to 250 °C (300 to 500 °F).

Solomon said the new spills are not related to geological activity at the nearby Seafloor Observatory that the cruise was headed toward. Instead, they occur near vertical faults that intersect the massive Cascadia subduction zone. These slip faults exist, where portions of ocean crust and sediment slide past each other, because the ocean plate strikes the continental plate at an angle, putting pressure on the upper continental plate.

Fluid loss from the marine giant front through these slip faults is significant because it reduces fluid pressure between sediment particles and thus increases friction between oceanic and continental plates.

“The Giant Rift Zone is like an air hockey table,” Solomon said. “If the fluid pressure is high, it’s like running air, which means there’s less friction and the two plates can slide. If the fluid pressure is lower, the two plates will lock—then pressure can build up.”

Solomon said the fluid oozing from the fault area is like a lubricant leaking. This is bad news for earthquake hazards: Low lubricant means stress can build up to cause a devastating earthquake.

Solomon said this is the first known site of its kind. He added that similar fluid leak sites may be located nearby, although they are difficult to detect from the ocean surface. A large liquid spill off central Oregon could explain why the northern part of the Cascadia subduction zone, off the coast of Washington, is thought to be locked or coupled more strongly than the southern part off the Oregon coast.

“The Pythias oasis provides a rare window into the processes working deep on the sea floor, and its chemistry indicates that this fluid is coming from near plate boundaries,” said Deborah Kelly, a professor of oceanography at the University of Washington. “This indicates that nearby faults regulate fluid pressure and massive slip behavior along the Cascadia central subduction zone.”

Solomon has just returned from an expedition to monitor seafloor fluids off the northeast coast of New Zealand. The Hikurangi subduction zone is similar to the Cascadia subduction zone but generates more frequent and smaller earthquakes which makes it easier to study. But Solomon said it has a different structure on the seafloor, which means it’s unlikely there could have been fluid leaks like the ones discovered in the new study.

The research was funded off Oregon State by the National Science Foundation. Other co-authors are Teresa Werley, who did the work as a doctoral student at the University of Washington and now works as an environmental consultant in Seattle. Emily Rowland, a former University of Washington faculty member now at Western Washington University; Masako Tominaga of the Woods Hole Oceanographic Institution; and Ann Trehough and Robert Collier at Oregon State University.

For more information, contact Solomon at [email protected] or Kelley at [email protected].

Tag(s): College of Environment • Deborah Kelly • Earthquakes and Seismology • Evan Solomon • Geology • College of Oceanography

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