On Mount Erebus, the tallest peak on Ross Island in Antarctica, there exists a molten lake of lava which constantly emits gas. The composition of that gas is unique in that it changes almost every ten minutes. Mount Erebus is an active volcano that has been bubbling for decades and within it it a crater that hold the 20 meter deep lake of lava. The lava in the lake reaches approximately 1000 degrees Celsius, which is quite the contrast with the air outside! Because of that contrast in temperature between the outside air and the convection currents which feed the lake, the lake's surface will not cool into hard rock.
Lava lakes require the specific structures of crater, conduit, and magma chamber in order to form. Without these structures, the convection currents cannot sustain the bubbling of the magma that composes the lake. Hence why there are only five molten lava lakes on the planet that have stayed bubbling in the last decade! Nevertheless, Mount Erebus's lava lake is special because it contains a rare type of magma called phonolite which is much thicker than the common basalt magma.
If you happen to be walking by a lava lake, beware of the degassing explosions that the lake might belch up from deep in its magma chamber belly. While this type of gas eruption is different from the more frequent shorter gas-emitting cycles, these eruptions are much more impressive!