If you could merge all known underwater mountains and active underwater volcanoes, their total area would be roughly equivalent to that of Europe and Russia combined. And the threats these habitats face, from warming oceans to commercial fishing to a controversial, nascent deep-sea mining industry, are mounting. Underwater volcanoes are “absolutely everywhere,” says Julie Huber, a marine microbiologist at the Woods Hole Oceanographic Institution. But what happens in international waters is another story, explains Matthew Gianni, cofounder of the Deep Sea Conservation Coalition. But most of the world’s seamounts, active volcanoes, hydrothermal vents, and oceanic plains are in international waters, which could, theoretically, be regulated through new international treaties.