Lava is one of the most awe-inspiring substances on Earth, whether it's flowing gently or blasting violently out of the ground. But what makes it switch between one or the other? To investigate the physics of interactions between lava and water, researchers from the University at Buffalo have conducted experiments on lab-made lava – with some explosive results.

Water and lava interact pretty regularly in nature, but the outcomes aren't always easy to predict. To get a better understanding, the Buffalo researchers mixed the two together under different circumstances to see what happens. The results could help us determine how safe or unsafe a particular eruption is to nearby communities, if occurring near bodies of water.

"Sometimes, when lava encounters water, you see huge, explosive activity," says Ingo Sonder, lead investigator on the study. "Other times, there is no explosion, and the lava may just cool down and form some interesting shapes. What we are doing is trying to learn about the conditions that cause the most violent reactions."

First, the researchers made 10-gallon (38-L) batches of their own lava by melting down basaltic rocks in a high-powered induction furnace. After four hours the mixture reaches 2,400° F (1,316° C), and it's then poured into an insulated steel box and injected with water.

The team ran 12 variations on the basic experiment, using different-sized boxes of between 8 and 18 inches tall (20 and 46 cm), and injecting the water at different speeds, between 6 and 30 feet per second (1.8 and 9.1 m).

The results varied. In some cases, the mix only gave off a little steam and threw small blobs of lava just above the surface. Other times large visible jets of steam burst forth, ejecting the stuff several meters in the air. Generally, the tests showed that the lava tended to be more explosive when the water was injected faster, and when there was more than about a foot of lava above it.

While the studies didn't examine why these factors might influence the different results, the researchers had their suspicions. One hypothesis was that when water is introduced slowly into lava, the outer edges of the "blob" of water vaporize, which creates a protective film around the water. That keeps any more of it from boiling away, trapping a bubble of water in the lava.

But if the water is injected more quickly, it ends up mixing with the lava more readily, so the protective vapor film doesn't have time to form. The water would continue to vaporize, that gas would rise and expand and once it reaches the surface, results in an explosive outburst from the lava.

The team acknowledges that only a few tests were conducted, so these observations are far from comprehensive. But they should provide a decent starting point for future experiments – and at the very least, they produced some pretty cool videos and photos.

The research was published in the Journal of Geophysical Research (JGR): Solid Earth. Check it out in the video below.

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