Lakes of Fire

Permanent lava only exists in a few places around the globe. One of the strangest lava lakes is the top of 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 10 minutes cycle.

Erebus was a Greek god, the son of chaos, which is kind of fitting for a placement 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 of Mount Erebus's main crater. Under that 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. Except it goes the other way, it does not goes down, it goes up. All of this in about 1000 degrees Celsius.

Even in the frigid Antarctic air the lake surface won't cool into solid rock, thanks to the convection currents that feed the lake with a steady supply of hot magma that rises to the top of the lake, and 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 of those components so well aligned. That's why the 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's 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.

Mt. Nyiragongo

One mystery they're working on is the lake 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 10 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 the 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 in composition doesn't really change, but the conduit also, occasionally, like every 10 minutes or so, burps out a large blob of magma from deeper in the chamber. 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 seemed to work independently. The composition of 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 a better model of the inner workings of Mount Erebus.

The volcano 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.

Hopefully the recent studies on Erebus will be useful for scientists working on other lava lakes around the world. 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.