Trapped by the terrain into depressions or pools, lava may remain fluid rather than solidifying.
These lava lakes may be fed with new hot lava pouring up from below Earth’s surface. Sooner or later, the lava’s channel collapses, stopping the flow of more lava.
Shallow lava lakes may harden after a year, but the deepest ones—up to 400 feet deep (about 120 meters)—can take a quarter of a century to cool and harden completely.
Some, however, disappear, sucked back down into their craters like water down a drain.