MAUNA LOA, Hawaii (KHON2) — The volcanoes here in Hawaii are basaltic volcanoes, and they create two kinds of lava: A’a and Pahoehoe. Both are made of the same thing–minerals and dissolved gases like water vapor, carbon dioxide and sulfur — but Professor Scott Rowland, a geologist in the Department of Geosciences at UH Manoa, said they are significantly different.

“A’a flows tend to be very rough and covered with loose stones, which we call clinkers. And, they can be anywhere from dust-sized up to almost car-sized. They’re just these really jagged, rubble basically. Pieces of — of lava that’s kind of been pulled apart and they make traversing an A’a flow really, really a chore,” Rowland explained. “Whereas Pahoehoe, on the other hand, is typically much smoother. It has a glassy surface.”

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Rowland said Mauna Loa’s eruption is currently producing A’a because it’s pumping massive amounts of lava that’s moving quickly down the side of the mountain. He said that is causing it to lose a lot of heat.

“And it’s got a lot of mass behind it, so it’s forced to still move, even after it has become quite viscous,” Rowland said. “And it’s that movement, while it is viscous, that causes it to tear apart and become A’a. So in general, if you look at the historic record, A’a flows are the fast ones, because they’re associated with high effusion rate at the event.”

That’s compared to Pahoehoe, which he said flows much slower and dries smoother.

“Right now that A’a flow front, I’ve been told, it’s about 60 feet thick which is impressive,” Rowland said. “So it’ll be many months before that thick portion of the flow cools down. But further upslope where the flows are considerably thinner, they will cool down in two to three weeks probably.”

An upside of an A’a flow is that if it does cover the highway, Rowland said it may be easier to clear because A’a is like poorly formed gravel and can be easily crushed with a bulldozer.

Every one of the Hawaiian islands was created by eruptions just like Mauna loa. While most areas on the older islands like Oahu have evolved over time due to weather and erosion, spots like the Ka Iwi coastline still look like volcanic rock all these millions of years later.

“The other cool thing is that around the world people use A’a and Pahoehoe, the Hawaiian words,” Rowland explained. “It started in the late 1800’s, mostly because American geologists were here in Hawaii looking at Kilauea and Mauna Loa and talking to Hawaiian people.”

According to Rowland there was initially some resistance to using the Hawaiian words.

“They didn’t want to use non-European words,” he explained.

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But, he said he’s glad A’a and Pahoehoe eventually stuck and worked their way into literature.

He said the only place that doesn’t refer to lava as A’a and Pahoehoe is Iceland.