An undersea volcano has erupted off the coast of Oregon, spewing forth a layer of lava more than 12 feet thick in some places, and opening up deep vents that belch forth a cloudy stew of hot water and microbes from deep inside the Earth.

Scientists uncovered evidence of the early April eruption on a routine expedition in late July to the Axial Seamount, an underwater volcano that stands 250 miles off the coast of Oregon.

The discovery came as a surprise, as researchers attempted to recover instruments they’d left behind to monitor the peak a year earlier. When the researchers hefted a seafaring robotic vehicle overboard to fetch the instruments, the feed from the onboard camera sent back images of an alien seafloor landscape.