Weird Ways People Have Tried To Stop Lava

When a volcano erupts, the conventional wisdom is that you evacuate, because there’s nothing you can do to stop the destructive power of the heat, ash, and lava that comes from it. But conditions vary. If a lava flow is some distance away, you might have quite a bit of time before it arrives. And in the past, some have even tried to stop or divert it. 

Before he was a general in World War Two, George S Patton designed a different kind of military campaign - a bombing run on Hawaii's Mauna Loa, the largest volcano on Earth, as it erupted in 1935.
As the lava began flowing at a rate of one mile (1.6km) a day towards the city of Hilo, then-director of the Hawaiian Volcano Observatory Thomas Jaggar suggested bombing lava tubes.
Lava tubes are cooled and hardened outer crusts of lava which provide insulation for the faster-flowing, molten rock inside. Such a conduit enables lava to move farther and faster.
In theory, bombs would destroy the lava tubes, robbing lava of an easy transport channel and exposing more of the lava to the air, slowing and cooling it further.
But in practice, while bombs created craters in parts of the tubes, they were soon filled again by the lava. Hilo was instead saved when Mauna Loa stopped erupting.

I dunno, stopping lava with bombs seems like trading a hot frying pan for fire. Other methods have been tried, with similar results. When the lava stops, it might have been because of human effort, or it might have been because they all stop sooner or later. Read about some of the schemes used to deal with lava at BBC Magazine. -via Smithsonian