In the last decade, residents of a remote corner of the Arctic started reporting startling and mystifying events: huge explosions and boulders shooting into the sky. Then they discover brand new, yawning holes in the ground; the biggest is more than 80 feet wide and 150 feet deep — large enough to swallow a 15-story building whole. Scientists had never seen anything like it, and wondered what could possibly be causing them.

On “Artic Sinkholes,” NOVA follows teams of U.S. and international scientists to Siberia and as they attempt to get to the bottom of this bizarre phenomenon. They find evidence that entire Arctic landscapes are ticking timebombs as vast amounts of methane, a potent greenhouse gas, are released by melting permafrost.

In Alaska, experts discover a lake the size of twenty football fields bubbling with methane from below and vast layers of frozen methane trapped under rapidly melting subsoil. Local communities recount their experience of a landscape shifting irreversibly right before their eyes.

What are the implications of these dramatic developments in the Arctic? Scientists and local communities alike are struggling to grasp the scale of the methane threat and what it means for our climate future.