Off the coast of Washington, columns of bubbles rise from the seafloor, as if evidence of a sleeping dragon lying below.
But these bubbles are methane that is squeezed out of sediment and rises up through the water. The locations where they emerge provide important clues to what will happen during a major offshore earthquake.
The first large-scale analysis of these gas emissions along Washington’s coast finds more than 1,700 bubble plumes, primarily clustered in a north-south band about 30 miles (50 kilometers) from the coast.
Scientists found the first methane vents on the Washington margin in 2009, and thought at the time they were lucky to find them. But since then, the number has just grown exponentially.
Results show, the gas and fluid rise through faults generated by the motion of geologic plates that produce major offshore earthquakes in the Pacific Northwest.
These vents are a little ephemeral. They’re not reliable, like the geysers at Yellowstone.
Sometimes they turn off-and-on with the tides, and they can move around a little bit on the seafloor.
They tend to occur in clusters within a radius of about three football fields.
The authors analyzed data from multiple research cruises over the past decade that use modern sonar technology to map the seafloor. Their new results show more than 1,778 methane bubble plumes issuing from the waters off Washington State, grouped into 491 clusters.
The vast majority of the newly observed methane plume sites are located at the seaward side of the continental shelf, at about 160 meters water depth.