Most volcanoes have a deep inner chamber of molten rocks, but this chamber is typically capped shut by cooled, solid rock. But sometimes the magma chamber is exposed at the top of the volcano in a giant caldera of rolling, bubbling and spluttering lava. This happens when an active volcanoes continuously pushes new molten rocks up the vent forming a pool inside the caldera while solidified lava sinks back into the depth to be re-melted. Volcanologists often describe lava lake as “windows into the heart of volcanoes.”

“Persistant lava lakes are very rare, and require a delicate equilibrium between heat supply and heat loss,” says VolcanoDiscovery.com. “Heat supply is provided by rising magmatic gasses from the magma chamber through a liquid-filled conduit, and is counterbalanced by intense heat lost at the surface of the lava lake.”

The lava lake of Mount Nyiragongo. Photo credit: Olivier Grunewald/Boston.com