Flow that nearly reached Pahoa still active

For the past year, lava flows from the Puu Oo vent have been following a familiar pattern.

Breakouts fan out across a northeastern flow field, adding new layers to the geologic record, while remaining within 5 miles from the cone on Kilauea’s East Rift Zone.

That’s good news for communities downslope largely spared from the surprisingly fast advance of the June 27 flow in 2014. But geologists say Puu Oo’s persistent 33-year-old eruption never follows the same pattern for long.

As they’ve noted before, change is the only constant when you’re dealing with volcanoes.

“It’s going to change; something is going to happen,” said Tim Orr, a geologist with the Hawaiian Volcano Observatory.

Orr was one of a handful of geologists who recently spoke with the Hawaii Tribune-Herald about the ongoing eruption a year after the threat level was reduced from a warning to a watch.

Typically, that change happens every three to four years, he said, adding the so-called June 27 flow is nearing two years of age.

“We’re probably going to see something happen, some eruption or some new breakout at the cone,” Orr said.

When that occurs, though, remains to be seen.

The flow, which started June 27, 2014, was the result of a new vent opening on the northeast side of the cone, where flows have been concentrated for the past several years.

Within a couple months, it was already threatening Pahoa, aided by both friendly topography and a surge of lava.

While the eruption rate remains stable, geologists say the June 27 vent occurred lower on the cone, allowing it to drain the reservoir, giving it a strong push downslope.

Fortunately for thousands of lower Puna residents, the flow ran out of steam twice within striking distance form Pahoa Village Road and Highway 130 — 14 miles from the flow’s source.

The stalling led to the flow becoming inactive at its leading edges, and lava being redirected near its source, where it has largely remained since. The lava tube that formed as a result of the flow has since closed up a few miles from the vent, geologists believe.

Without a similar draining of the reservoir, or an increase in eruption output, geologists say it will be difficult for the flow to travel the same distance.

But that doesn’t mean there are no communities at risk.

“This is something we are watching,” said Orr, while pointing on a map to a finger of lava on the northern edge of the flow field.

The lobe is tracing a “path of steepest descent” that would take it to Hawaiian Acres. As of this week, it was about 5 miles from the subdivision.

“If it were to capture more of the flow, more of the activity, it might become more concerning,” said Orr, adding it has traveled about a mile in a month.

But until it does, the lobe is expected to continue to help the flow field widen without prompting HVO and county officials to consider warning residents downslope.

One benefit of the flow threatening Pahoa is geologists have been able to better refine their predictions.

Geologist Matt Patrick said use of thermal cameras, a technique introduced during the 2014-15 lava scare, allow scientists to see all activity on the flow field, not just what’s at the front, during aerial observations.

He said that allows them to adjust their models and better predict whether a breakout will redirect the flow somewhere else.

“In this case we get precise locations,” he said.

Overall, Puu Oo’s lava output remains far below what it was five or six years ago, when activity was concentrated on the south side of the vent.

Orr said lava output is about 1 to 2 cubic meters per second, down from 4 meters.

Does that mean the eruption is waning?

Orr said it could just be part of a long-term cycle, adding the eruption could last for decades more.

“It could be the end of it,” he said. “It could be the start of it. Who knows.”

Email Tom Callis at tcallis@hawaiitribune-herald.com.