Kilauea Volcano’s three-month eruption last summer pushed roughly 1 billion cubic yards of molten rock across the Lower Puna landscape and left lava more than 900 feet thick where the flow collided with the ocean.

The Hawaiian Volcano Observatory last week published a preliminary map showing for the first time how thick the cooled lava is from the eruption that buried 13.7 square miles and added some 875 acres of new land to the island.

Although a final map will be released after additional data is collected, the preliminary figures indicate there are varying levels of lava thickness.

The region with the greatest amount of lava — ranging in thickness from 180 to 919 feet — was found in the newly formed land created where lava entered the ocean around the former Kapoho Bay and coastal region to the south.

The thickest pileup of lava inland was not the 100-foot-tall cinder cone known as fissure 8, the vent in Leilani Estates that at times blasted lava more than 200 feet in the air and became the main source of the flow during most of the eruption.

That distinction went to fissure 22, just southeast of Puna Geothermal Venture power plant. Its estimated lava thickness is 180 feet.

Hawaiian Volcano Observatory geologist Janet Babb explained that the slope around fissure 8 caused lava to flow away from the prolific vent, leaving only 167 feet of cooled lava there.

The larger lava mass at fissure 22 was caused by a combination of smaller flows and fountaining that allowed lava to pile up near the vent, she said. Additionally, lava filled a natural depression in the vicinity of the fissure, she said.

Scientists collected some 1,500 aerial photos and used surface-from-motion software to produce a digital elevation model of the lava eruption. They compared the new digital model with a similar one of the pre-eruption landscape to figure out the relative thickness.

But certain regions of the flow field couldn’t be photographed during the eruption, Babb said, either because drones couldn’t be launched close enough to the target areas or a toxic laze plume from the ocean entry was blowing over the area, creating unsafe conditions for helicopter overflights.

Now that the eruption is over, aerial photos and other data can be collected from these areas, she said, and the project might be finished in six months to a year.

Babb said the thickness of the newly formed coastal land is impressive but not surprising considering there were no major lava delta collapses during the eruption.

That in itself was unexpected, she said, because major lava delta collapses occurred regularly whenever lava entered the ocean over the past 35 years of Kilauea’s eruption from Puu Oo.

Two years ago, for example, the greater part of a 26-acre lava delta suddenly crumbled into the ocean at Kamokuna, even taking with it an older coastal cliff that was home to a public viewing area. While no one was hurt during that event, lava deltas in general are considered dangerous.

Babb said the offshore slope around Kapoho was not as steep, which apparently allowed the lava entering the ocean to cool and pile up with more stability.

“The thickness there was impressive,” she said.

Stretching from May 3 to Aug. 4, the voluminous Lower Puna eruption destroyed 716 homes, forced the evacuation of 2,000 residents, covered 30 miles of roads, isolated 1,600 acres of farmland and caused damage estimated at more than $800 million.

Scientists said the volcano produced enough lava to fill at least 320,000 Olympic-size swimming pools, with most of it pouring out of fissure 8 at rates exceeding 100 cubic meters per second to feed a fast-moving river of lava that wound its way to the ocean more than 4 miles away.

It was the largest lower East Rift Zone eruption and caldera collapse in at least 200 years, according to a study published last month in Science magazine and authored by dozens of Hawaiian Volcano Observatory scientists and others.

According to the paper, the lava’s high rate of speed was due to a combination of factors, including the pressure within the volcano’s plumbing system and the relatively low elevation of the eruption site, which allowed gravity to coax the magma downslope from the summit.