Scientists at the U.S. Geological Survey's Hawaiian Volcano Observatory have been monitoring every twist and turn of lava creeping unpredictably toward communities in a rural and isolated district on the Big Island.

Their work can be dangerous and includes frequent flyovers in a helicopter, navigating precarious terrain and taking careful data measurements to give the public an accurate picture of the lava's progress.

"To do that you have to walk across a lava tube, and that's fairly hazardous work," said Janet Babb, a geologist who also serves as the observatory's spokeswoman.

Photos taken by the observatory this week include a shot of a geologist wearing protective clothing while using a radar gun to measure the speed of the lava flow. A wider shot shows another scientist noting his measurements of the volume of lava flowing through the tube.

"That's important to know because that tells us what's feeding the flow front," Babb said.

To obtain those measurements, geologists have to make sure the ground they're dealing with is stable enough. To measure the speed of lava, a geologist needs to find a skylight — an opening on the roof of the tube — that can be safely accessed, Babb said.

The measurements help Hawaii County Civil Defense officials prepare for the lava, which the observatory estimated could cross the Puna district's Highway 130 in 13 days. In order to prevent residents from being cut off from the rest of the island, county workers are busy preparing defunct, unpaved roads to be used as alternate routes.

On Wednesday, the lava had advanced about 350 yards from the previous day within a vacant lot in the Kaohe Homesteads subdivision. Officials were hopeful the flow would bypass homes.

Babb said that those in her field have a fascination for the wonders of volcanos.

"This is our line of work, but at the same time, it is with heavy hearts that we see this flow approach critical infrastructure and disrupt people's lives," she said. "When a lava flow is going into the ocean ... it's not impacting anyone's life directly, it's easier to stand back and sort of enjoy the beauty of that. But when the flow is headed for infrastructure ... that makes it hard."

Before the public became concerned about the lava, the observatory's scientists were already keeping close tabs on the lava, which they call the June 27 flow because that when it emerged from a vent. The observatory issued a news release on Aug. 22 letting the public know it was advancing.

"And it wasn't an easy decision because we didn't want to alarm people unnecessarily," Babb said. "Now that we look back, we're convinced it was the right thing to do."

Residents at packed community meetings on lava updates often preface their comments or questions with gratitude for the scientists' work, county spokesman Kevin Dayton said.

"I think it's because the scientists who work up there have been there a long time," he said. "They're not strangers. They're people who have been in the community many years."