Studying magma before it erupts is a big challenge for geologists for a variety of reasons, not the least of which is the fact that the molten rock sometimes sits inaccessible miles below the earth’s surface.
But recent research by University of Hawaii professor Bruce Houghton, Hawaii Volcano Observatory’s Don Swanson and colleagues from the University of Cambridge is giving scientists a glimpse into magma and giving them some understanding of why some eruptions explode and others do not.
In examining lava from 25 of Kilauea’s eruptions that took place in the past 600 years, Houghton and his colleagues found tiny portions of molten rock trapped in crystals in the cooled lava. Houghton said to think of the crystals as tiny jars with sealed lids.
“Some of the time, it’s as though the lid isn’t perfect,” which allows some of the trapped gas in the magma to escape, Houghton said.
The molten rock “tries to reach the conditions” on the outside, causing some gases to leak, he said.
In analyzing those crystals, scientists found that the “amount of leakage is proportional to the speed it comes to the surface,” he added.
They also learned that incidents with magma with more gas, and that comes to the surface more quickly, are likelier to end in an explosive eruption.
“That gas that’s left powers the powerful explosions,” Houghton said. “If your concern is bigger, more powerful eruptions, look at magma that moves quickly from tens of miles below the surf, not the last few thousand feet.”
That’s contrary to what scientists thought made the difference between powerful eruptions and less explosive ones, he added.
One step to finding those quickly moving flows is being able to accurately detect where magma is moving and how, which is something scientists are trying to do better than they can now, Houghton said.
Their research was published this week in “Nature Geoscience.” Swanson and Houghton “supplied a framework of very well-characterized eruptions using a detailed classified scheme for the size and power of the eruptions,” a press release said, while Cambridge scientists “performed nano-scale measurements of the original gas content of the magmas as ‘frozen’ in tiny packets of chilled melt inside large crystals in the magma.”
Houghton also found some unexpected information in the results.
“What intrigued us was that we weren’t anticipating the variation that we found within this data,” Houghton said this week.