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Researchers discover unique underwater spring, Pythia’s Oasis, with potential implications for earthquake risk in the Cascadia Subduction Zone

Researchers from the University of Washington have discovered a unique underwater spring named Pythia's Oasis, which is located about 50 miles off Newport, Oregon. The paper detailing the discovery was published in the journal Science Advances on 25 January 2023.[0] The spring emits warm, chemically distinct fluid which is sourced 2.5 miles beneath the seafloor at the plate boundary.[1] It is believed that Pythia's Oasis helps to control stress on the offshore fault by drawing its energy from this water. After observing plumes of methane bubbles at a depth of almost a mile below the ocean's surface, the team uncovered the leak.[0] After sending an underwater drone, the researchers discovered that water with a different chemical composition from the surrounding seawater was seeping into the ocean from a hole in the ground “like a firehose.”[0]

The team found that the water was 16 degrees Fahrenheit warmer than the seawater around it.[0] The fluid is estimated to come from the Cascadia megathrust, where temperatures are an estimated 150 to 250 degrees Celsius (300 to 500 degrees Fahrenheit).[1] The reduction of fluid at the offshore megathrust interface by means of strike-slip faults has significance as it decreases the pressure of fluid between the sediment particles, thus leading to heightened friction between the continental and oceanic plates.[2] This can lead to an increased risk of earthquakes.

The team made the discovery during a weather delay of the RV Thomas G. Thompson.[1] Bubble plumes were detected by the ship's sonar at a depth of approximately 0.7 miles beneath the water's surface, which was unexpected.[1] The bubbles were discovered to be merely a minor component of the warm, chemically unique fluid spilling from the bottom sediment after further investigation utilizing an underwater robot.[1]

Pythia's Oasis is a newly discovered seafloor seep on the Central Oregon segment of the Cascadia Subduction Zone. The unique chemical composition of the fluid suggests that the nearby faults regulate fluid pressure and megathrust slip behavior along the central Cascadia Subduction Zone. The discovery of Pythia's Oasis provides a rare window into processes acting deep in the seafloor.

According to Evan Solomon, a UW associate professor of oceanography and seafloor geology specialist, the “megathrust fault zone is like an air hockey table. If the fluid pressure is high, it’s like the air is turned on, meaning there’s less friction and the two plates can slip. If the fluid pressure is lower, the two plates will lock—that's when stress can build up.”[2] Solomon added that the new seeps aren’t related to geologic activity at the nearby seafloor observatory that the cruise was heading toward.[1] They happen in the vicinity of vertical faults that intersect the extensive Cascadia Subduction Zone. Strike-slip faults are formed when oceanic crust and sediment move in opposite directions, caused by the angle at which the oceanic plate collides with the continental plate, resulting in stress on the continental plate above.[1]

According to Solomon, this site is the first of its kind to be discovered.[3] There could be comparable fluid seepage locations in the vicinity, but they are difficult to identify from the surface of the ocean.[1] A significant fluid leak off central Oregon could explain why the northern portion of the Cascadia Subduction Zone, off the coast of Washington, is believed to be more strongly locked or coupled than the southern section off the coast of Oregon.[1]

Overall, the discovery of Pythia's Oasis provides important insights into the processes at work deep in the seafloor and highlights the importance of understanding fluid pressure and megathrust slip behavior along the Cascadia Subduction Zone.

0. “A Leak at the Bottom of the Sea May Be a Harbinger of Doom” Yahoo! Voices, 11 Apr. 2023, https://www.yahoo.com/news/leak-bottom-sea-may-harbinger-180932935.html

1. “Scientists discovered chemically distinct liquid shooting up from the Oregon seafloor” Tech Explorist, 11 Apr. 2023, https://www.techexplorist.com/scientists-discovered-chemically-distinct-liquid-shooting-up-from-the-seafloor/58706

2. “Scientists Discover Leak in the Bottom of the Ocean” Futurism, 12 Apr. 2023, https://futurism.com/leak-bottom-ocean

3. “Warm liquid spewing from Oregon seafloor comes from Cascadia fault, could offer clues to earthquake hazards” Phys.org, 11 Apr. 2023, https://phys.org/news/2023-04-liquid-spewing-oregon-seafloor-cascadia.html

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