The U.S. Geological Survey has made numerous overflights of lower East Rift Zone lava since the current eruptive phase of Kilauea volcano began May 3, but an overflight of the summit and Volcano village area on Wednesday morning had a different purpose.

Kyle Anderson, a USGS research geophysicist on loan from California Volcano Observatory, said Thursday that USGS personnel in a helicopter were using a tool called LiDAR — an acronym for light detection and ranging — “to build a digital elevation model of the summit.”

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“There are two main purposes of the mission,” Anderson said. “To build the full-scale elevation model to look for changes in volume and the gross topography of the summit, and the second is looking for new cracks and small slumps and things that we wouldn’t be able to detect any other way, especially in trees.

“What they’re doing is shooting laser energy from the helicopter down to the ground, timing the return, and using that to build an elevation model.”

The overflight area included, in addition to the summit itself, part of Hawaii Volcanoes National Park, Volcano village and Volcano Golf and Country Club.

“The idea was to extend a bit outside the topographic caldera to make sure there was no cracking going on, faulting in any regions outside the caldera,” Anderson said.

The numerous collapse-explosion events at Halema‘uma‘u crater have caused dramatic changes to Kilauea’s caldera area, and the almost continuous seismic activity at the summit likely was the cause of a recent sinkhole in Highway 11 which since has been repaired.

Anderson said USGS had been using drones — which they refer to as unmanned aerial vehicles, or UAVs, — to map the caldera.

“The UAVs have struggled recently because of the high winds, so we have not had an elevation model of the summit in some time,” Anderson said. He added that LiDAR is “truly the best tool we have in monitoring changes in the topography of the summit and the way the eruption is progressing.”

Anderson said scientists are “still processing” the data gathered from Wednesday’s LiDAR overflight. He described the computer models under construction as “incredibly precise and detailed.”

“The model itself is three-dimensional,” Anderson said. “What we’re going to have is the height of every point in the caldera, so that’s a three-dimensional model. Then, you have to display it on a two-dimensional screen, so you can spin it around in space. What we usually do is build shaded terrain models so you simulate a light source and it gives the perception of depth when you look at it on a screen. The data itself is three-dimensional but, of course, we have to display it in a two-dimensional way.”

Anderson said the new model will be compared to previously collected data to help scientists learn more about what is happening at the summit and how it affects residents nearby.

“There was a LiDAR scan of the summit way back in 2009, so that’s sort of our baseline, and then there was another one that was done during the eruption. I don’t have the exact day, but that was a few weeks ago. So we have a couple of previous images to compare it to. These can also be compared to the images from the UAVs to a certain extent, as well.”

Hawaiian Volcano Observatory spokeswoman Janet Babb said that in addition, future models from LiDAR and drone overflights will be compared to the model constructed from Wednesday’s overflight.

“That will allow us to resolve by what mechanism and how quickly things are changing in the caldera,” Babb said in an email. “After the current activity ends, these data will likely continue to be used in a variety of ways (some unforeseen), informing more detailed studies of faulting, the structure of Kilauea caldera, etc.”

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Babb added that the model, and what is learned from it, will be shared with Civil Defense, the National Park Service and other emergency managers.

Email John Burnett at jburnett@hawaiitribune-herald.com.