Sonder and Harp high-five and allow themselves a small moment of celebration - the results were similar to an earlier experiment that they were trying to replicate. They trot down the hill to the metal frame to inspect the scene.
Fine pieces of volcanic shrapnel sparkle across the equipment and ground up to a few meters away. Some have landed in jet-black beads and jagged splashes, others are fragile ephemeral glass bubbles, and still others have stretched out into blonde glass fragments that coat the experimental setup, a form of solidified lava known as Pele's hair.
They watch the footage from the explosion. Interestingly, in this iteration, the explosion appears to have started not with the impact of the hammer, but with the injection of the water, potentially giving them insight into the process of the explosion.
"There's almost more water than melt," Harp says, pointing at the video.
Sonder and Harp have run the experiment more than 20 times since 2015 and have seen a wide variety of results. There have been large explosions and small ones. Occasionally, no explosion at all. More data is needed for them to come to any conclusions about their early results, but they think they're on the right track.
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This summer, they'll be adding a more powerful water pump in an effort to re-create even more explosive conditions. They hope to eventually be able to quantify and characterize why the water-lava interaction makes the molten rock explode. That information could improve hazard maps meant to better inform people living in the shadow of the volcano about water-related volcanic dangers.
"Water is everywhere," Sonder notes, even near active volcanos. "You can't keep people from building in areas that are otherwise good for building," he goes on, not even if there is a potential danger from a nearby volcanic eruption in the future.
But it is possible to develop accurate ways to assess the hazards of a volcano, including the probability of large explosive events when lava or magma encounters ice or water. For that to be done, we'll first have to figure out how such explosions unfold at the most basic level.
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