She is petite, trim, almost birdlike. He’s big, slightly lumbering, closer to a bear. Her hair is short, kept in a shaggy pixie cut. His resembles an unruly, curly mop — a Chia pet in full sprout. Both of them have very large ears. No one can remember exactly how they met; it might have been on a bench at a university, or at a movie screening, or perhaps on a blind date. What we do know is that Katia and Maurice Krafft bonded over a common obsession: volcanoes. And by the time they’d married in 1970, these two scientists had already started trotting the globe together to study these beautiful, violent natural phenomenons whenever and wherever eruptions occurred. “Certain colleagues see us as weirdos,” Katia admitted. The first couple of volcanology, however, simply recognized each other as soulmates.

It’s a miniature irony that Fire of Love, Bay Area documentarian Sara Dosa’s portrait of a romance, opens in what appears to be a raging blizzard — if there was ever a movie characterized by extreme heat, it’s this one. Not just the kind radiating out of spewing solar-orange geysers and flowing, pulsing molten streams, all of which are captured in 16mm footage shot by either colleagues of the volcanologists or the Kraffts themselves. (The fact that National Geographic picked the film up out of Sundance isn’t the least bit surprising, given the absolutely astonishing footage that Dosa and co. found in the couple’s archive; that it’s also getting a theatrical run co-sponsored by a distributor named, appropriately enough, Neon is simply kismet.) There’s also a palpable sense of high-temp intensity that you feel just watching these two whenever they’re traipsing alongside a glowing chasm in the earth’s crust, as if they’d somehow sublimated a sexual passion for a shared one. The doc is a capsule history lesson on an eons-old natural phenomenon. But it’s also the greatest lava-fueled love story ever told, and the fact that those two elements remain as inseparable as the spouses at the center of it all is a testament to how sublime this stranger-than-fiction masterpiece really is Dosa has referred to her painstakingly assembled recounting of the Kraffts’ lives as a tale of a “love triangle.” And indeed, the volcanoes act as a floating third party in their amour fou, with each new scaled peak and rockpile beguiling them separately and collectively. In the Kraffts’ minds, these were partners in crime. During a vintage TV interview, Maurice is quick to poo-poo “lazy categorizations” regarding the different volcanoes they’d visited, and claimed that each had their own distinct personality. (The movie even takes that notion one step further, giving “co-starring” credits to Mauna Loa, Nyiragongo, Una Una, Krafla, and Mt. St. Helens.) He will acknowledge, however, that you can divide volcanoes into two basic types: “red” ones, which are the result of tectonic plates moving part and are what you usually picture when someone says the word “volcano”; and “gray” ones, which happen when those plates come together and build pressure underneath the surface. The latter are explosive, ash-belching and much more dangerous. These are the ones that arouse Katia and Maurice’s interest the most. They were also play a part in the couple’s demise.