Lava tubes are basically nature’s version of subway tunnels, except instead of commuters they carry molten rock at temperatures hot enough to vaporize anything foolish enough to get in the way. And they form through a process so weirdly specific that it’s almost hard to believe it happens at all.
When Volcanoes Build Their Own Plumbing Without Asking Permission
Picture this: a volcano erupts, and lava starts flowing downhill like the world’s most destructive river. The surface of this flow cools first—because physics—forming a crusty shell while the interior stays liquid and keeps moving. It’s the geological equivalent of a lava burrito, if burritos could melt through steel.
Here’s the thing: that crusty roof acts as insulation.
The lava beneath stays molten and continues flowing downhill, carving out a tunnel as it goes. Eventually the eruption stops, the remaining liquid drains out like someone pulled a plug, and you’re left with an empty tube. Hawaii’s Kazumura Cave stretches for 40.7 miles—the longest lava tube on Earth—and it formed exactly this way during eruptions from Kilauea volcano roughly 500 years ago. Standing inside one feels like being swallowed by a sleeping dragon.
The Temperature Game That Nobody Wins Except Geologists
Basaltic lava flows—the runny, low-viscosity kind—are the only ones that really pull off this trick. They flow at temperatures around 1,100 to 1,200 degrees Celsius, which is hot enough to glow like a malevolent nightlight. Thicker, more viscous lavas like andesite or rhyolite? They’re too sluggish, too prone to just piling up in domes rather than flowing far enough to build tubes.
Turns out the speed matters too.
Fast-moving flows develop thicker roofs that can support themselves even after the lava drains. Iceland’s Surtshellir cave, formed around 1,100 years ago, has ceiling thickness of up to 30 meters in some spots—basically a geological parking garage roof. Slower flows tend to collaps before they can create anything substantial.
Why Some Planets Get All the Cool Underground Architecture
Mars has lava tubes too, and they’re absurdly huge. The lower gravity means Martian tubes can grow to widths of 250 meters or more without collapsing—ten times bigger than Earth’s. Scientists identified several candidates using data from NASA’s Mars Reconnaissance Orbiter in 2017, including one near Pavonis Mons that could theoretically shelter entire human colonies. Moon’s got them too: the SELENE spacecraft found a skylight in 2009 that drops into a tube possibly 50 kilometers long.
Wait—maybe the most fascinating part isn’t how they form but what happens after. These tubes become time capsules, preserving delicate lava formations called lavacicles (yes, that’s the actual term) and maintaining constant temperatures year-round. Some Hawaiian tubes stay at exactly 16 degrees Celsius regardless of surface conditions. Ancient human cultures used them as shelters; modern scientists see them as potential habitats for future Mars colonists.
The irony? These structures created by one of nature’s most violent processes become some of the most stable, protected environments on any planetary surface.
