Cradling one of the world’s largest and least studied lava lakes—more than 700 feet across and possibly miles deep—Nyiragongo has twice sent molten rock racing toward residents of Goma.

A member of the expedition walks on the caldera’s cooled lava floor, turned red by the reflected glow of the lake. It’s a low-frequency rumbling that pulses through your body—like being inside a giant subwoofer.”

Constant bubbling sends waves of lava lapping over the rim. Scientists aren’t sure of the lake’s depth, though recent lava samples indicate the magma originated in the Earth’s mantle more than 46 miles below.

With temperatures around 1800°F, the lava lake is wildly erratic. As molten rock meets the air, it cools and forms plates on the lake’s surface.

Rising gas bubbles explode, splattering lava up to 60 feet in the air over Nyiragongo’s fiery lake.

The lava at Nyiragongo is made of an alkali-rich volcanic rock; its unusual composition may be a factor in the lava’s fluidity.