Large-scale volcanic experiments
Lava-water interactions are associated with a phenomenon known as a molten fuel coolant interaction, in which a liquid fuel (a heat source) reacts violently with a liquid coolant. Much of the experimental work in this field has been done in the context of industrial safety, with a focus on understanding potential dangers in nuclear power plants and metal production sites.
The lava-water experiments build on previous research in this area, while focusing on molten rock.
The work takes place at UB’s Geohazards Field Station in Ashford, New York, some 40 miles south of Buffalo. Run by the UB Center for Geohazards Studies, the facility gives scientists a place to conduct large-scale experiments simulating volcanic processes and other hazards. In these tests, researchers can control conditions in a way that isn’t possible at a real volcano, dictating, for example, the shape of the lava column and the speed at which water shoots into it.
To make lava, scientists dump basaltic rock into a high-powered induction furnace. They heat it up for about 4 hours. When the mixture reaches a red-hot 2,400 degrees Fahrenheit, it’s poured into an insulated steel box and injected with two or three jets of water.
Then, a hammer drives a plunger into the mix to help stimulate an explosion. (In some cases, if enough molten rock was present above the injection point, an intense reaction began before the hammer fell).
In addition to identifying some preliminary trends, the published study attests to the wide variety of physical processes that can occur when lava and water meet.
“The system response to water injection varied from mild, evaporation-dominated processes, in which only a little melt was ejected from the container alongside some steam, to stronger reactions with visible steam jets, and with melt domains ejected to several meters height,” the scientists wrote in JGR: Solid Earth.
The study did not examine why box height and water injection speed corresponded with the biggest explosions. But Sonder, whose has a background in geosciences and physics, offers some thoughts.
He explains that when a blob of water is trapped by a much hotter substance, the outer edges of the water vaporize, forming a protective film that envelops the rest of the water like a bubble, limiting heat transfer into the water and preventing it from boiling. This is called the Leidenfrost effect.
But when water is injected rapidly into a tall column of lava, the water — which is about three times lighter than the lava — will speed upward and mix with the molten rock more quickly. This may cause the vapor film to destabilize, Sonder says. In this situation, the unprotected water would expand rapidly in volume as it heated up, imposing high stresses on the lava, he says. The result? A violent explosion.
In contrast, when water is injected slowly into shallower pools of lava, the protective vapor film may hold, or the water may reach the lava’s surface or escape as steam before an explosion occurs, Sonder says.
He hopes to explore these theories through future experiments: “Not a lot of work has been done in this field,” he says, “so even some of these basic processes are really not well understood.”