For the latest research, Burton's team examined the spectrum of infrared light emitted by red-hot blobs of magma.
By finding out which wavelengths were absorbed by the air above the crater, the scientists were able to determine precisely which gases were present.
And by comparing gas emissions during and between bursts, they found differences in composition indicating that the gas slugs originated at a depth of about 10,000 feet (3,000 meters) beneath the crater.
That is approximately the base of the mountain, where it rests on the seabed.
"The gas phase driving the explosions preserves the memory of hotter—but also deeper—source conditions," the scientists wrote.
Other scientists studying Stromboli are pleased with the findings.
"It's a nice complement to what seismology can do," said Bernard Chouet, a geophysicist with the U.S. Geological Survey in Menlo Park, California.
Prior research used a network of seismic stations to determine that the conduit feeding the volcano flares wider about 800 feet (250 meters) beneath the surface, Chouet said.
Rather than originating in this region as previously believed, gas slugs rise quietly from below until they reach the area and have more room to expand, the new study suggests.
"That produces a piston-like action of the liquid 250 meters [820 feet] down," Chouet said.
Together, the study and older seismic models are producing a better overall picture of the volcano's plumbing, he noted.
The work has global significance, because other volcanoes are known to produce strombolian eruptions.
Learning more about the source of the gas can also help researchers better understand why some volcanoes produce relatively benign eruptions while others are more explosive.
"It's providing an added component," Chouet said, "to the model of slug formation."
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