How to Douse Lava

While updating my article on Sicily's Mount Etna, I had occasion to read about the efforts in Iceland to stop lava flows with firehoses. That was in 1973, when the volcano Eldfell, on the island of Heimaey, sent a flow of lava toward the town of Vestmannaeyjar. Given a big enough hose and water pressure, pumping seawater on the active flow was quite effective in freezing it in its tracks. A single hose, scientists found, could cool an entire hectare because as the cooling lava cracked it allowed the water to penetrate in all directions. (The problem was getting equipment of the right caliber to the scene.)

Being scientists, they checked by drilling holes. "In the boreholes, the cooling extended down to depths of 13 to 15 m, after cold water had been poured on the lava for about two weeks. A hole was bored in an area which had not been cooled by water, and molten lava was encountered directly below the surface." The whole report is online from the U.S. Geological Survey.

Also:
Eternal Etna
About Volcanoes
About Volcanism
Drilling into Volcanoes