A massive volcano is silently building pressure beneath the Pacific—and could blow at any moment.

The Axial Seamount, located 300 miles off Oregon’s coast and nearly a mile underwater, has swelled to the same level seen before its last eruption in 2015.

That event triggered 8,000 earthquakes and sent lava flows surging across the seafloor.

Scientists say it’s showing all the signs of another eruption, though it’s too remote to threaten coastal communities.

Still, the eruption will offer a rare chance to study one of Earth’s most active submarine volcanoes in real time.