Effusive sedimentary volcanism experimentally reproduced under Martian-like conditions
This study demonstrates through experiments and modeling that rapid boiling under Martian-like low-pressure conditions actively sustains sedimentary volcanism by driving coupled ballistic-effusive mud eruptions, rather than suppressing them as previously assumed.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Imagine you are a detective trying to solve a mystery about how planets get their bumps and bruises. For a long time, scientists have been puzzled by strange, muddy-looking hills and rivers on Mars and on icy moons like Europa. They look like they were made by volcanoes, but there's a problem: the air on Mars is so thin (almost a vacuum) and so cold that if you spilled a bucket of water there, it should instantly boil, freeze, and turn into a solid block of ice. It's like trying to make a snowball in a blast furnace; the physics suggests that liquid mud shouldn't be able to flow or build mountains because it would freeze before it could move. This is the big question: How could "mud volcanoes" ever happen in such a hostile, freezing environment? To understand this, we need to know a few things. First, "metastable liquid" is just a fancy way of saying a liquid that is technically unstable and wants to change state (like water that wants to boil or freeze) but hasn't quite done it yet. Second, "sedimentary volcanism" is when mud or slurry erupts from the ground, building cones or flowing like lava, but made of wet dirt instead of hot rock. Finally, "cryovolcanism" is the icy version of this, where water or slush erupts on frozen worlds. The mystery is whether these liquids can actually stay liquid and flow long enough to build the landforms we see, or if they just freeze solid immediately.
Now, enter a team of scientists who decided to stop guessing and start building a mini-Mars in a lab. They wanted to see what happens when you take a bucket of wet, muddy slush and suddenly expose it to the thin, cold air of Mars. Instead of just pouring mud into a vacuum chamber (which would freeze it too fast), they came up with a clever trick. They built a "pressure cooker" made of ice. They took a tray of sand, froze it, and then poured their special mud mixture (water, magnesium sulfate, and clay) into a hole. Then, they let the surface of that mud freeze over, creating a hard, icy lid. This lid trapped the liquid mud underneath, keeping it safe and pressurized. Once the lid was strong, they heated the bottom of the tray just a tiny bit. This heat weakened the ice lid from below until it popped!
When that ice seal burst, the trapped mud was suddenly exposed to the low pressure of the chamber (about 4.5 mbar, which is like the air pressure on Mars). The scientists expected the mud to instantly freeze and stop moving. Instead, something wild happened. The sudden drop in pressure made the trapped water inside the mud boil violently. This boiling didn't stop the eruption; it powered it. The bubbling created pressure that shot the mud out of the ground like a geyser.
The experiment showed that the eruption happened in two distinct acts, kind of like a rock concert. First, there was a "ballistic" phase. The boiling mud shot out in little droplets and chunks, flying through the air and landing in a ring around the hole. It looked like a fountain of mud. Some of the smaller droplets flew far away, while the bigger, heavier chunks landed right next to the vent. Here's the magic part: even though the outside of these droplets froze instantly into a thin, icy shell (like a chocolate coating on a hot fudge pudding), the inside stayed warm and liquid. Because they landed close to the vent, they piled up.
Then came the second act: the "effusive" phase. As the mud kept piling up near the hole, it started to merge. The warm, liquid centers of the frozen droplets melted together, forming a continuous, flowing river of mud that spread out across the sand. The eruption evolved from shooting mud into the air to slowly oozing it out, building a little cone and flowing down the sides. The scientists found that the size of the underground "reservoir" mattered a lot. A smaller reservoir made a neat, steep cone, while a bigger reservoir kept the mud flowing for longer, creating wider, flatter flows.
The paper suggests that this process—where boiling drives the mud out, and the flying chunks pile up to form a flowing river—is exactly how those strange mud volcanoes on Mars might have formed. It proves that rapid boiling and freezing don't stop the mud; they actually help it move and build structures. The researchers used computer models to check if the mud would stay warm enough during its flight, and the math says yes: the droplets stay liquid inside long enough to land and flow. While the experiment was small (using a tray about the size of a coffee table) and the mud was a simple mix, the results strongly suggest that the laws of physics allow for these muddy eruptions to happen on Mars and other icy worlds, even in the freezing cold. It turns out that the very thing we thought would kill the eruption (the boiling) is actually the engine that keeps it going.
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