Slow Motion Chaos: Why Bombs and Fences Won't Stop Hawaii's Lava

For the Hawaiian town of Pahoa, there is no easy way to stop the smoldering lava pouring from the Kilauea volcano.

In other places and at other times, people have blasted molten rock with seawater, built barriers, and even dropped bombs on lava to keep it from destroying property. But when the 2,000-degree river hits Pahoa, residents will be able to do little more than watch.

Kilauea on Hawaii's Big Island has been continuously erupting since 1983, with most of the lava flowing into the ocean. A new vent began spewing molten rock in June. The lava is now at the doorstep of Pahoa, threatening the homes of its nearly 1,000 residents.

The big problem is that while lava flows can be diverted they can't be stopped entirely, and it's very hard to predict where they will go.

"Suppose you create a diversion and it happens to work," Peter Cervelli, associate director of science and technology for the USGS Volcano Science Center, told NBC News.

"You might save your house, but it diverts to your neighbor's house, and you have just created a problem for somebody else," he said.

People think of lava as an all-consuming fire that destroys everything in its path. But occasionally you will see molten rock flowing around a tree.

How is that possible? Once lava comes into contact with something cooler than itself, the outer layer will form a crust. Build a berm made of rock, dirt or other material that is high enough and the new crust will form a barrier.

That is what was done in 1983 at Mount Etna in Italy, where multiple mounds of rock and ash were constructed to stop lava from destroying the tourist area of town. Evidence shows that people have been trying this method for hundreds of years.

Building a barrier can work, but unless the lava stops on its own, it's only a temporary solution.

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Slow Motion Chaos: Why Bombs and Fences Won't Stop Hawaii's Lava