In 1973, residents of Heimaey, Iceland, did something that sounds completely bananas: they sprayed seawater on a lava flow. For five months, they pumped 6.8 billion liters of frigid ocean water onto molten rock creeping toward their harbor, trying to freeze it in place. And here’s the thing—it actually worked.
When Molten Rock Meets Human Desperation and Garden Hoses
Lava flows at temperatures between 700°C and 1,200°C, which means stopping one is roughly equivalent to redirecting a river made of liquid hell. Yet humans have been trying for centuries, because what else are you supposed to do when a geological blowtorch is heading toward your town?
The Icelanders weren’t the first.
Back in 1669, citizens of Catania, Sicily, tried digging trenches to divert Mount Etna’s lava away from their city. They wore wet cowhides for protection—imagine medieval firefighters in leather onesies—and actually managed to redirect the flow. Until residents from a neighboring town showed up with weapons, furious that the diverted lava was now threatening their homes instead. That’s about as dramatic as volcanology gets: competing villages in a literal turf war over who gets buried in igneous rock.
The Physics of Freezing Something That Shouldn’t Be Frozen
Turns out you can’t just throw water at lava and call it a day. The Heimaey operation required coordinating 43 pumps working around the clock, creating a solidified crust that slowed the flow’s advance. The trick wasn’t stopping the lava entirely—that’s physically impossible—but cooling its leading edge enough to redirect its path. Think of it like building speed bumps out of frozen rock while the road itself keeps melting.
In Hawaii, authorities have tried bombing lava flows. Twice. In 1935 and again in 1942, the U.S Army Air Corps dropped explosives on flows from Mauna Loa, attempting to disrupt their channels. The 1942 effort might have worked—the flow stopped shortly after—but geologists still argue whether the bombs helped or the lava just ran out of steam naturally. Either way, the optics of bombing your own state are, shall we say, questionable.
Barriers, Walls, and Other Exercises in Geological Futility
Mount Etna has become Europe’s testing ground for lava-stopping infrastructure. In 1983, engineers built earthen barriers to protect the town of Nicolosi. The lava simply went around them. In 1991-1992, they tried again with massive barriers and explosive channeling during a 473-day eruption. This time, they saved the town of Zafferana Etnea—but only after the lava had already destroyed a chunk of it.
Wait—maybe we’re thinking about this wrong.
The problem isn’t just that lava is hot. It’s that lava flows represent stupendous amounts of thermal energy in motion. A single cubic meter of basaltic lava contains enough heat to boil roughly 3 million liters of water. You’re not fighting a substance; you’re fighting thermodynamics itself, and thermodynamics has a notoriously undefeated record.
The Uncomfortable Truth About Geological Timescales and Human Ambition
Modern volcanologists mostly advocate for a different strategy: get out of the way. Tokyo has evacuation plans for Mount Fuji. Iceland relocates people rather than attempting heroic engineering. The U.S. Geological Survey’s official stance on stopping lava flows could be summarized as “good luck with that.”
Yet humans keep trying, because surrendering to a slow-moving wall of rock feels absurd. Lava flows typically advance at walking speed—sometimes just meters per hour. You can literally outrun them. But you can’t out-wait them, and you definately can’t negotiate with them. They’ll consume your house, your town, your infrastructure with the patient indifference of geological process.
The Future Might Involve Robots or Resignation Probably Both
Some researchers propose using autonomous robots to build barriers in real-time, deploying swarms of heat-resistant machines to construct walls faster than humans safely could. Others suggest advanced modeling to predict flow paths decades in advance, allowing cities to simply not build in danger zones. Both approaches require admitting something uncomfortable: nature operates on timeframes where human lifespans are rounding errors.
The Heimaey operation succeeded because the flow was relatively small, the water supply unlimited, and the community desperate enough to try something that sounded like science fiction. Those conditions rarely align. Most lava flows happen in places without ocean access, or move too fast for water-cooling, or simply overwhelm any human intervention with sheer volume.
So can we stop a lava flow? Technically, sometimes, under specific conditions, with enormous resources and luck. Should we try? That depends whether you value your town more than you fear looking foolish while spraying water at a river of molten rock. The Icelanders made their choice. The rest of us are still figuring out ours.
