Hank: Earth is covered in lakes. Mostly these are cool, watery affairs full of life and great for a relaxing vacation. Lava lakes are a little less serene: they’re scorching, seething pools of molten rock. They’re also pretty rare, outside of MineCraft. Permanent lava lakes only exist in a few places around the globe.

One of the strangest lava lakes is atop Mount Erebus, on the frozen continent of Antarctica. Probably the weirdest thing about this lake is that it’s constantly releasing gas, and the composition of that gas changes on a roughly ten-minute cycle.

Erebus was a Greek god, the son of Chaos which is kinda fitting for a place made of ice and fire. Mount Erebus is the tallest peak on Ross Island, which lies close to the Antarctic mainland and is usually connected by ice sheets. It’s an active volcano that’s been bubbling away for decades, occasionally throwing off larger eruptions.

The lava lake is around 20 meters deep, and it sits in a crater which is itself inside Mount Erebus’s main crater. Under the lake is a conduit, a tube that leads down to a chamber full of magma underground lava, in other words. The lake is basically like a bowl with a hole in the bottom sitting on top of a pipe - like a sink, I guess you could say except it goes the other way: it doesn’t go down, it goes up. And all of it’s about a thousand degrees Celsius.

Even in the frigid Antarctic air, the lake’s surface won’t cool into solid rock thanks to convection currents that feed the lake with a steady supply of hot stuff. Hot magma rises to the top of the lake, then spreads outward, cooling off along the way. As it cools it gets denser, so it sinks back down again – and the convection cycle continues.

Lava lakes need that crater, conduit, and magma chamber combo to exist, and not many volcanoes have all those components so well aligned. That’s why molten lava lakes are super-rare there are only about five on Earth that have remained persistently active in recent years.

So the Mount Erebus lava lake is an unusual and remote place, but thanks to some intrepid scientists, it’s an area of active research. Scientists have braved freezing slopes and burning lava bombs, that’s the technical term for flying blobs of lava. And they’ve installed remote sensors to keep tabs on the lake 24/7.

One mystery they’re working on is the lake’s persistent gas emissions. For years, Erebus has been steadily releasing a gas plume, and there’s a weird cycle to it. Over the course of ten minutes or so, there’s a repetitive shift in both the amount of gas produced, and its composition — the overall mix. For example, the carbon dioxide to carbon monoxide ratio changes, as do emission levels of water vapor and sulfur dioxide.

Researchers have been trying to figure out why there’s this repeating cycle, and based on sensor data and computer modeling, they think it has to do with two main sources of gas. One comes from the conduit, and the other comes from diffusion in the lake. The carbon dioxide-rich gas is always rising up from the conduit, and it’s basically constant the amount and composition doesn’t really change. But the conduit also occasionally, like every ten minutes or so, burps out a large blob of magma from deeper in the chamber, like a kind of literal one-way lava lamp.

Once a blob gets near the surface of the lake it releases a fresh set of gases, which adds to the total amount of gas detected and changes the overall composition because it’s rich in water vapor and sulfur dioxide.

In addition to these shorter cycles, the lava lake also has what researchers call explosive degassing. These less frequent but more impressive belches cause small eruptions, hurling lava bombs into the main crater. The two systems seem to work independently. The composition of the gas from the explosive degassing is different from the gas from the shorter cycle, and appears to come from much deeper in the volcano’s magma chamber.

There is still a lot left to learn about Erebus, and lava lakes in general. For example, there are gas cycles with other cycle lengths that aren’t as well studied. Working out if they’re connected, and how, will build up a better model of the inner workings of Mount Erebus.

Mount Erebus also contains a rare type of magma called phonolite. It’s much thicker than the more common basalt variety, which probably affects the fluid dynamics inside the magma chamber and lake. So hopefully the recent studies on Erebus will be useful for scientists working on other lava lakes around the world.

These lakes may be rare, but having good models from the few examples around the world will help geologists understand the similarities and differences between them and the overall rules about how they work.

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