Blasting lava with an air cannon may not have been the best way to re-create a volcanic eruption, but Erika Rader and her colleagues persevered.
The scientists were attempting to make volcanic “spatter bombs,” or blobs of lava that sometimes get launched during moderately explosive eruptions. Rader and her colleagues wanted to create spatter bombs because, as she noted, they’re “a difficult thing to study in nature while they’re being produced” at the explosive center of a volcanic eruption.
Spatter bombs can be found around long-dead volcanoes on Earth as well as around volcanoes across the solar system. These researchers can’t zip through space or time, so they resigned themselves to creating spatter bombs all on their own—using leaf blowers, air cannons, and, finally, a shovel.
Rader, a volcanologist at NASA’s Ames Research Center in Mountain View, Calif., presented the research on 21 March at the annual Lunar and Planetary Science Conference in The Woodlands, Texas.
A Spatter of Knowledge
In nature, spatter bombs form in two main ways, and these both involve gas, Rader explained. Gas is what makes a volcano explosive, so sometimes the volcano erupts in a way that throws out blobs of lava.
“Spatter bombs are like volcano loogies,” Rader said. They’re “blobs of mostly molten lava launched into the air that usually pile up into cones and ridges near the vent of a volcano.”
Another way spatter bombs form is when gas builds up in a stream of lava flowing away from a volcano. Lava could encounter water, for example, and a flash of steam could launch a spatter bomb into the air.
Once spatter bombs smack into the ground and cool off, they become a treasure trove of information about the volcano they came from, Rader said. Spatter bombs can tell a scientist how explosive a volcano was. The size of a spatter bomb’s air pockets can give researchers clues on how much gas the volcano held. These air pockets can also reveal whether there was any water on the surface or in the ground around the volcano.
For scientists studying eruptions that they can’t witness up close—like volcanoes that erupted millennia ago or on other planets—these are all important characteristics to know, Rader explained. For example, anyone trying to piece together the history of Mars’s atmosphere could look at Martian spatter bombs to see how much gas a volcano contributed.
“Bombs can only form if the temperature conditions are right,” Rader said. The lava can’t be too hot, or a blob won’t even form—it’ll just be a flow. It can’t be too cold either, or the resulting material will be too brittle to fuse together. “Basically, we’re using spatter as an indicator of eruption conditions,” she continued. If the researchers can pinpoint the exact temperatures at which these spatter bombs form, they can perhaps, from spatter bombs they find in the field, untangle the eruptive characteristics of a given volcano.
But before scientists can start to study different eruption conditions, they need a better idea of the physical properties of spatter bombs as they form. So Rader and her team decided to create their own spatter bombs down here on Earth.
Trial and Error
Scientists around the world have simulated impact craters, riverine flow, and even lava flow in controlled conditions. But no such technique exists for spatter bombs.
So Rader and her team simply winged it.
First, they needed a way to create their own lava. Luckily, Syracuse University in New York has a special furnace to do just that, so that’s where the researchers headed.
They also wanted the lava to be propelled into the air somehow, like natural spatter bombs, so they started with a leaf blower. At first, team members crouched at the end of the furnace’s trough, where the lava pours out, and blasted the dribbling lava with air.
That didn’t work so well, Rader said. Instead of blobs, the leaf blower method just produced these “very pretty deposits,” Rader said, “this lacy, needly thing.”
So the researchers tried an air cannon. Surrounded by parked cars. During freshman move-in week. There were streams of students “waiting to go up to their dorms to drop off their stuff, and we were blowing lava all over the place,” Rader said.
But like the leaf blower, the air cannon created long, hot needles of lava, not suitable spatter bombs.
Their third attempt involved pouring lava into a mold and dropping it from about 3 meters up in the air to simulate an impact scenario, Rader said. But that didn’t work, either, because the hardened lava blob would break like an egg and all its molten insides would pour out.
After some more experimentation, the researchers finally found their groove. While the lava poured down the furnace’s trough, a scientist clad in a heat-proof onesie stopped it with a shovel and then used the shovel to knead the lava blob like pizza dough. Someone else simultaneously threw gravel at the blob to start the cooling process. After it started to cool into a thickened blob, the researchers picked it up with heavy-duty pliers and dropped it on a platform to cool completely.
Watch a video of the process here:
Not the perfect recipe for spatter bombs—nothing is flying through the air, after all. But it’s a start at least, and Rader noted that the structures found within the homemade spatter bombs match closely enough with their natural counterparts.
During the process in which the spatter bombs formed, the researchers measured the lava’s temperature to get a range in which the features form. Once the lava cooled, they measured the size of the bombs and their temperature, as well as how much their surfaces fuse when they cool on top of each other.
Next will be to start testing variables—for example, what happens when the bombs encounter water? How long do the bombs take to cool when they’re piled on top of each other? The researchers also want to do experiments that account for different gravities, like on the Moon and Mars. Knowing at what temperatures these structures form and how long they take to accumulate and cool can be a first step in investigating the eruptive history of volcanoes on our world and beyond.
—JoAnna Wendel (@JoAnnaScience), Staff Writer
Wendel, J. (2018), Homemade “spatter bombs” can reveal volcanic secrets, Eos, 99, https://doi.org/10.1029/2018EO095463. Published on 23 March 2018.
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