In “Fire of Love” the voice-over quotes Maurice and Katia Krafft’s feelings about the risks in their line of work: exploring and filming volcanoes. “I prefer an intense and short life to a monotonous, long one,” Maurice wrote. Katia acknowledged the danger but said that in the moment she didn’t care at all.

The Kraffts, married French volcanologists, were killed June 3, 1991, observing an eruption of Mount Unzen in Japan. But the stunning 16-millimeter footage they shot throughout their careers — full of gushing lava, flying rocks and giant clouds of smoke — lives on in the new “Fire of Love,” an all-archival documentary compiled from roughly 200 hours of their material along with 50 hours of TV appearances and other clips.

“I have so many questions that I wish I could have asked them personally, and one of them is what reels didn’t make it,” Sara Dosa, the documentary’s director, said in June during an interview in Tribeca. After all, visiting volcanoes is fraught with hazards. The film tells of Maurice scalding his leg in boiling mud and shows him playfully testing Katia’s helmet by throwing a rock at her head. Dosa said they didn’t use “a fun shot we had of Maurice taking his melted boot and throwing it into a lava flow.”

It’s safe to assume that not all of the couple’s film equipment survived, either.

But “Fire of Love” is not just about the Kraffts’ time in the field; it’s also about their lives and their marriage. Dosa, who learned about the couple while doing research for a previous documentary, has described her film as a love triangle involving Maurice, Katia and the volcanoes.

The movie tries to stay true to them — “we always wanted to start with Katia and Maurice, first and foremost,” Dosa said — while maintaining some critical distance. A voice-over from Miranda July expands on and at times complicates the Kraffts’ descriptions, countering Maurice’s claim, for instance, that he was “not a filmmaker,” but merely “a wandering volcanologist forced to make films in order to wander.”

The couple — short-haired, bespectacled Katia; bushy-maned, garrulous Maurice — toured the world giving lectures and holding screenings. Even today, in part thanks to their many books and TV appearances, they enjoy a measure of global fame.

“We wanted to kind of explore how they were crafting their own image as well,” Dosa said. “They seemed to understand that their public image helped them to continue to live the lives that they wanted to lead. They performed versions of themselves, not in a way that was inauthentic at all — it seemed to be almost this higher truth of who Katia and Maurice were.”

Bertrand Krafft, Maurice’s older brother, now 82, maintained the footage after the couple’s deaths. “My parents didn’t know anything about photography and cinema, and Katia’s parents didn’t, either,” he said, speaking by phone through an interpreter. “Somebody had to take charge to manage the assets that Maurice and Katia left behind, and I was the only person who was available to do that.”

Bertrand has granted permission for Maurice and Katia’s images to be used in other documentaries. Indeed, another feature that makes use of the Kraffts’ material, “The Fire Within: Requiem for Katia and Maurice Krafft,” directed by Werner Herzog, had its premiere at Sheffield Doc/Fest in Britain on June 26. But Bertrand said the film he participated in the most over the years has been Dosa’s.

“Her ideas, her approach to the project, seemed excellent to me,” he said. “That’s why I did anything I could to be able to help her.”

THE FOOTAGE included fully finished movies and working materials both edited and not, according to Mathieu Rousseau of Image’Est, the French archive that had been storing the Krafft collection of 800 reels of film and 300,000 slides. (Bertrand Krafft sold the material to a Geneva- based company, Titan Film, after the documentary was underway.)

“What was complicated in the beginning, and also when we had to digitize everything to be able to allow Sara to be able to make her movie, was that we needed to figure out what Maurice had done,” Rousseau said through an interpreter during a video call. Maurice, he noted, “did the editing himself. He had his own logic.”

Dosa and her editors also had to make sense of the hundreds of hours of footage. Jocelyne Chaput, one of the editors of “Fire of Love,” said that on some reels, “I got the impression that someone had swept the cutting-room floor of Maurice’s house and then respliced it all together, and that was that reel.”

Erin Casper, the other editor, said that making sure they were staying accurate — with footage that was loosely arranged geographically but not necessarily chronologically — was difficult as well.

Furthermore, none of the Kraffts’ 16-millimeter footage had sound; all the audio of churning lava, for example, had to be added. The finished version of “Fire of Love” draws on a mix of Foley effects and a library of field recordings that the sound designer, Patrice Le­Blanc, said had been accumulated over 30 years.

Using sound wouldn’t have been alien to Katia or Maurice, Chaput and Casper suggested: Some of the Kraffts’ films used sound effects or voice-over, or would run while Maurice was lecturing over them.

KEN HON, the scientist in charge at the U.S. Geological Survey’s Hawaiian Volcano Observatory, knew the Kraffts beginning in the late 1980s, and remembers that filming volcanoes then was unusual.

“There wasn’t a lot of footage of volcanic eruptions at that time, and certainly not stuff that was up close,” he said. “You had to be a volcanologist to film like they did because you had to be able to point the camera at the correct thing to understand the process that’s going on.”

Today such footage is much more common thanks to lighter and cheaper equipment. Maurice, he said, “would be so in love with drones right now.”

When the Kraffts traveled through Hawaii, Hon recalled, he sometimes accompanied them into closed areas, like the village of Kalapana when it was overrun by lava in 1990.

Filming “was just like second nature to them,” he said. “They’re setting up cameras and continuing to chat,” never pausing to say, “Stop, I have to focus, I have to concentrate.” Hon had some appreciation for the challenges the Kraffts faced: He helped his wife and fellow volcanologist, Cheryl Gansecki, make videos for about 20 years.

“High temperatures, it’s usually wet and there’s the acidic gas coming out of the volcanoes, right?” he said. “The combination of those things are exactly what they tell you not to immerse your electronic item into.”

Steven Brantley, a volcanologist who retired after 37 years with the Geological Survey but has returned part time, said that even when the Kraffts’ footage might make it appear that they were in harm’s way, they positioned the camera “in such a way that they could walk in front of it and live to tell the tale, over and over and over,” he said. “So in that sense I think they were very careful, even though it may not look like they were.”

Hon also didn’t think of the Kraffts as incautious. “The kind of eruption that got them at Unzen, the dome-forming eruptions with collapses and small explosions and things, those are the most dangerous kinds of eruptions because they’re so unpredictable,” he said.

The New York Times reported at the time that the couple and another volcanologist, Harry Glicken, who died with them, “had no chance to escape when the pyroclastic flow from the main crater, 2 miles away, plunged down the slope at a speed estimated at 100 to 125 mph.”

Brantley, whose career included 21 years at the Hawaiian Volcano Observatory, never worked with the Kraffts in the field, but did collaborate with Maurice on a video about volcanic hazards that was nearly complete when Maurice died. Sections of it were screened in time to warn Philippine residents of the eruptions at Mount Pinatubo that occurred less than two weeks later. Brantley emphasized that educating the public about volcanoes was as much a part of the Kraffts’ legacy as their striking footage.

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