Something strange was going on 50 miles off the coast of Newport, Oregon, deep beneath the Pacific. Water was blasting upward out of the seafloor with a force that stunned the scientists watching. It was not supposed to be there. And the more they studied it, the more unsettling the picture became.
A ship got delayed, and everything changed
The discovery began almost by accident. A research team made the find during a weather-related delay for a cruise aboard the RV Thomas G. Thompson, when the ship’s sonar picked up unexpected plumes of bubbles about three-quarters of a mile beneath the ocean’s surface.
Researchers sent an underwater drone down to look. What they found stopped them cold.
Water with a different chemical composition from the surrounding seawater was seeping into the ocean from a hole in the ground “like a firehose,” said Evan Solomon, a University of Washington oceanographer and co-author of the study.
“That’s something that I’ve never seen, and to my knowledge has not been observed before,” Solomon said.
The delay that made the discovery possible had been a minor inconvenience to the crew. It turned into one of the most consequential detours in recent Pacific seafloor research.
The hole had a temperature that told a deeper story
Observations from later cruises confirmed the fluid leaving the seafloor is 16 degrees Fahrenheit warmer than the surrounding seawater. That gap is not a small thing at the bottom of the ocean, where temperatures hover close to freezing.
Calculations suggest the fluid is coming straight from the Cascadia megathrust fault, where temperatures are an estimated 300 to 500 degrees Fahrenheit.
Estimated fluid flow rates are orders of magnitude higher than those measured anywhere else along the margin, likely driven by extreme overpressures along the plate boundary.
That pressure, it turned out, was the real story. And the creatures living near the vent, including the deep-sea sponges and tube worms that cluster around such vents worldwide, were thriving above forces most life never touches.
The chemical signature of the fluid told scientists it had been traveling upward for a very long time, pressed through rock and sediment from depths that instruments can barely reach.
The fault beneath the fault
The Cascadia Subduction Zone is a 620-mile-long fault stretching from Northern Vancouver Island to Cape Mendocino in Northern California, separating the Juan de Fuca and North American plates.
Where the two plates meet, friction locks them together. Stress builds for centuries. Eventually the plates lurch, producing a megathrust earthquake with violent shaking and tsunamis that grow as they reach shallow coastal waters.
The last such event registered magnitude 9.0, in 1700. It dropped the Oregon coast several feet in seconds, drowned forests whole, and sent a tsunami across the Pacific that Japanese records captured the same night.
Pythia’s Oasis and the air hockey table
The study, led by the University of Washington and published in Science Advances, describes the underground spring the researchers named Pythia’s Oasis, discovered about 50 miles off Newport, Oregon.
Observations suggest the spring is sourced from water 2.5 miles beneath the seafloor at the plate boundary, regulating stress on the offshore fault like a pressure valve draining from somewhere almost unimaginably deep.
Solomon described the megathrust fault zone as “like an air hockey table.” If fluid pressure is high, the two plates can slip more easily. If pressure is lower, the plates lock, and that is when stress builds toward rupture.
A significant fluid leak off central Oregon could help explain why the northern Cascadia zone, off Washington State, is believed to be more strongly locked than the southern section. The fault stress picture across the entire West Coast is now being redrawn.
What this means for the millions of people in the Pacific Northwest
Earthquake experts note that some water leaking from the ocean floor is normal, and this particular seep has probably been active for at least 1,500 years. Researchers emphasize that this discovery does not change the current assessed risk of a major Cascadia rupture.
According to a study from the Proceedings of the National Academy of Sciences, there is a 15% chance of a rupture in the Cascadia Subduction Zone in the next 50 years, and a 29% chance by the year 2100.
Pythia’s Oasis is the first known site of its kind, though similar fluid seep sites may exist nearby, making them hard to detect from the surface. That is precisely why scientists say mapping them matters so much.
“Pythia’s Oasis provides a rare window into processes acting deep in the seafloor, and its chemistry suggests this fluid comes from near the plate boundary,” said co-author Deborah Kelley. Every new seep found is another data point, another chance to understand the clock before it runs out.