This article was originally featured on The Conversation.
Fountains of lava erupted from the Sundhnúkur volcanic system in southwest Iceland on Jan. 14, 2024. As the world watched on webcams and social media, lava flows cut off roads and bubbled from a new fissure that invaded the outskirts of the coastal town of Grindavík, burning down at least three houses in their path.
Nearby, construction vehicles that had been working for weeks to build large earthen dams and berms in an attempt to divert the lava’s flow had to pull back.
Humans have tried many ways to stop lava in the past, from attempting to freeze it in place by cooling it with sea water, to using explosives to disrupt its supply, to building earthen barriers.
It’s too soon to say if Iceland’s earthworks will succeed in saving Grindavík, a town of about 3,500 residents, and a nearby geothermal power plant. As a volcanologist, I follow these methods. The most successful attempts to stop or reroute lava have involved diversions like Iceland’s.
Why lava is so hard to stop
Lava is a sluggish, viscous fluid that behaves somewhat like tar. It is subject to gravity, so like other fluids, it will flow downslope along a path of steepest descent.
With the temperature of its molten rock often well above 2,000 degrees Fahrenheit (1,000 Celsius), not much can stand in its way.
Freezing lava in its tracks
In 1973, Icelanders attempted the most famous “lava freezing” experiment. They used water hoses from a flotilla of small boats and fishing vessels to protect the small island community of Heimaey from the Eldfell volcano’s lava.
The lava flows were threatening to close off the harbor, which is critical to the region’s fishing industry and a lifeline to the Icelandic…
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