I don’t think there’s a need to ‘plug the hole’. The article suggests that there’s hot water flowing out from under the sea bed but what’s more likely (and normal) is that there’s a fracture of exposed magma that’s heating the water at the seabed. This heated water is convecting up and mixing with the surrounding sea water, with the hot water mixed to ambient sea temperature before it hits the surface. The methane is normal from such fractures. They’re not normally permanent features and are analogous to magma flows on the surface of the earth.
The whole premise of the article and paper is that the water its self is from the plate boundary. "The seep fluid chemistry is unique for Cascadia and includes extreme enrichment of boron and lithium and depletion of chloride, potassium, and magnesium. We conclude that the fluids are sourced from pore water compaction and mineral dehydration reactions with minimum source temperatures of 150° to 250°C, placing the source at or near the plate boundary offshore Central Oregon."
