PUNA, BIG ISLAND (HawaiiNewsNow) - Twenty-four fissures have opened up in Leilani Estates since eruptions started May 3, but none have been more active than fissure no. 8.
The fissure opened up south of the Leilani Avenue and Luana Street intersection on May 5.
On Friday, the fissure was spewing an estimated 26,000 gallons of lava per second, creating fountains over 200 feet high.
It's also the fissure responsible for creating a channelized flow that covered much of Kapoho, destroying hundreds of homes, before filling Kapoho Bay. And it's still going, reshaping the Big Island as lava cascades into the sea, creating new land and producing a large plume of volcanic haze.
So what's up with no. 8? Why is it so active — and how long will it remain that way?
Ken Rubin, chairman of the Department of Geology and Geophysics at the University of Hawaii, said fissure no. 8 has been fascinating to watch from the very beginning.
"If you recall the early days of the eruption, it was also the only fissure that made a significant lava flow into the Leilani neighborhood," he said. "Then it seemed to shut down for a while, when other fissures, especially 19, 20, 22, started being very active, and then things shifted back to 8."
Rubin said it can be helpful to think of fissures as cracks that form to relieve the stress of magma injected into the subsurface of a volcanic area — in this case, the lower east rift zone.
As magma fills the area, pressure is relieved through these cracks in the ground. And that is when lava eruption occurs.
"Fissure eruptions often initiate with multiple active fissure segments and then focus down activity to just a small number," Rubin said, "in part because the amount of pressure from the magma to keep all the segments open is difficult to maintain."
For example, a 1955 eruption in lower Puna initially had many active fissures. But over time, just two continue to shoot out lava.
Previous eruptions of Mauna Loa — in 1942 and 1984 — also showed similar behavior.
"We usually expect fissure eruptions to mostly focus to one or a few close vents," Rubin said, adding that the eruptions in lower Puna appear to "have reached a stable condition for now, where the majority of the magma flux is at this spot, but I emphasize, for now."
And, he added, while previous eruptions can serve as a guide, there's no way to predict what might happen next during active volcanic event.
Experts say other fissure segments could open or old ones could reactivate as the volcanic system adjusts to changing conditions in the subsurface.
Rubin says these changes cannot be monitored in detail.
"We don't have a good idea of the actual shape of the plumbing system in the subsurface, and so physical changes in stresses in the ground and the amount of magma flowing at any one time can affect how and where magma finds the easiest pathway to the surface," he explained.
For now, though, the magma's easiest pathway to the surface is fissure no. 8., and Rubin says that may be why its erupting at such extreme rates.
"When that supply is (condensed) into fewer and fewer open fissures as time goes on, the vigor and intensity of lava flows will increase, just like when you restrict the open part of a garden hose with your finger to get a more directed spray," Rubin said. "More intense lava flows have a greater chance of flowing farther and causing more damage to structures and property along the flow path than feeble lava flows."