What they discovered had nothing to do with the original plan. In 2014, while the research team on board the RV Thomas G. Thompson was waiting out a weather delay, oceanographer Brendan Philip, a graduate student at the University of Washington at the time, noticed something strange in the ship’s sonar readings: columns of bubbles rising from the seafloor about 50 miles off the coast of Newport, Oregon, about three-quarters of a mile below the surface. The bubbles came as a surprise.
To conduct an investigation, they dispatched a remotely driven vehicle. Seafloor geologist Evan Solomon described what appeared on the Thompson’s screens as water emerging from the seafloor “like a firehose”—a warm, chemically unique fluid that gushed upward from a hole in the silt at the Pacific Ocean’s bottom. The group gave it the name Pythia’s Oasis in honor of the ancient Greek oracle who gave prophesies from a temple situated above a fissure in the ground that released gasses capable of affecting perception.
After years of follow-up missions, the discovery—which was reported in January 2023 in Science Advances—is noteworthy for reasons that go far beyond the peculiarity of discovering a warm spring on the ocean floor. The spring controls the load on the offshore fault by drawing water from the plate boundary, which is located 2.5 miles below the seafloor. One of the most monitored and feared seismic features on the continent is the Cascadia Subduction Zone, a fault that runs along the Pacific Northwest coast where the Juan de Fuca Plate slides beneath the North American Plate.
According to calculations, the fluid flows directly from the Cascadia megathrust, where temperatures are thought to be between 150 and 250 degrees Celsius. The spring is a unique direct pathway to what’s happening at the fault boundary itself because it reaches the seafloor at all instead of dissipating or being absorbed into the rock on the way up.
The UW team realized they were witnessing something truly exceptional due to the composition of the fluid that was reaching the seafloor. The liquid is depleted of magnesium, potassium, and chloride and enriched with boron and lithium. This signature is so clear that it rules out common cold seep processes and clearly indicates origin circumstances at extremely high temperatures and depths.
The study’s co-leader, oceanography professor Deborah Kelley of UW, called Pythia’s Oasis “a rare window into processes acting deep in the seafloor.” These activities reveal that fluid is actively moving from the plate boundary toward the surface, which is crucial information for comprehending the behavior of the fault.
Because it makes the mechanics understandable, Solomon’s comparison of the megathrust fault zone to an air hockey table has been frequently cited. High fluid pressure operates as if the air has been turned on; friction decreases and the plates may move more readily. The plates lock when the pressure drops. Additionally, locking is where the risk increases. Stress might accumulate when the two plates lock due to a decrease in fluid pressure.
It’s possible that the fluid escaping through Pythia’s Oasis is relieving pressure that would otherwise prevent the plates from gently slipping past one another. The team has made it clear that this finding does not alter the current risk profile for the Cascadia zone. However, researchers are cautious not to answer with more certainty than the data supports whether that makes a big earthquake more or less likely in any particular time span.
Reading the research gives me the impression that the discovery of Pythia’s Oasis is one of those scientific moments where an unintentional observation made during a weather delay opens a door that was previously invisible. For many years, the Cascadia Subduction Zone has been the subject of extensive research. This was unlike anything anyone had previously discovered.
The number of such sites along the fault, whether the fluid outflow is constant or varies over time, and the precise implications of these fluctuations for seismic risk modeling are still unknown. In an attempt to compare the behavior of Cascadia, Evan Solomon later traveled to the Hikurangi Subduction Zone off the coast of New Zealand to study a similar fault that produces smaller, more frequent earthquakes. The questions are already being altered by the spring at the bottom of the Pacific.
