A dark comedy with a tone as bracing as its icebound setting, “Force majeure” is about the impact of a near-miss encounter with an avalanche on a family’s domestic dynamic, but its effect is more like that of a cinematic glacier slowly and unremittingly taking its emotional toll on the characters, who move abruptly from farcical to tragic mode. Ruben Ostlund’s film emerges as a remarkable blend of dramatic power and bleak humor, though some viewers may be slow to pick up on the joke.

As the film opens, a Scandinavian family—father Tomas (Johannes Bah Kuhnke), mother Ebba (Lisa Loven Kongsli) and children Vera (Clara Wettergren) and Harry (Vincent Wettergren)—have arrived for a ski vacation at a modernistic, architecturally striking Alpine resort. After taking a few group photos, they begin their five-day sojourn, which will be followed chronologically, with trips down the slopes interrupted by scenes in their suite. On the second day—announced by a title card—the defining moment happens as they’ve settled into a table at an outdoor restaurant for lunch. In the distance an avalanche can be glimpsed moving in their direction—apparently just one of the controlled events set off by the resort staff via the booms that occur intermittently on the soundtrack. But this one appears to be coming at them implacably, gathering strength in the process. As it approaches and begins spraying the diners with snow, Ebba gathers the children under her maternal wing, as it were. Tomas, on the other hand, grabs his gloves and phone and sprints off to safety, returning only after the danger has passed.

That instantaneous decision becomes a sore eating away at the family. The kids’ demeanor subtly changes, and later grows increasingly frightened and surly as Ebba brings up Tomas’ cowardly act, first over dinner with an acquaintance (Malin Dahl) who openly flaunts her infidelity (and brings along a handsome young stud, played by Brady Corbet, to prove it) and then in a wine-driven all-nighter with Tomas’ old friend Mats (Kristofer Hivju), a divorced guy accompanied by Fanni (Fanni Metelius), a pretty, much younger girlfriend. Tomas insists he didn’t run away, and says that he and Ebba are merely remembering things differently. But watching the episode unfold on Tomas’ phone camera forces him to accept the truth about himself, and he finds it devastating.

“Force majeure,” of course, isn’t about the power of the avalanche as a physical phenomenon, but the destructive effect that brief encounter with it has on this apparently picture-perfect family. Tomas and Ebba are the ones affected the most, of course; he’s reduced in the end to a sobbing husk of his former self, and though he’s afforded an opportunity to redeem himself somewhat during a final stint in the snow with Ebba, it’s obvious he’ll never be the same person. Nor will Ebba. Though she reconciles herself to what happened—as least as far as we can see—she’s become the dominant figure of the pair, as shown in a postscript during the bus trip down from the mountain, when an inept driver’s inability to control the vehicle leads her to take charge.

But Tomas and Ebba aren’t the only ones to suffer. Vera and Harry are clearly affected too, hunkering down together as they see their father reduced to weeping and terrified that their parents might be on the brink of divorce. And Mats and Fanni are as well, not only in terms of the strains that appear in the friendship between Mats and Tomas during a day they spend together skiing, but in the heated discussion Mats and Fanni have after their conversation with the married couple—which threatens to sunder their relationship by proxy, as it were. Meanwhile a quiet hotel maintenance man watches silently as Tomas and Ebba argue through their troubles, as much a voyeur as we are.

The casting throughout “Force majeure” is impeccable. Kuhnke, who looks a bit like Peter Sarsgaard, conveys both Thomas’ amiability and his descent into despair, while Kongsli evinces both the concern and anger of his wife. The Wettergren children are no less remarkable, expressing in very few words how stress between parents can devastate their kids; and Hivju and Metelius persuasively play a couple whose reaction to an unpleasant encounter with friends is a mixture of amazement, amusement and contention. The ambience of the picture is equally important, with cinematographer Fredrik Wenzel’s cool, crisp widescreen images capturing the chilliness of both the locales and of Josefin Asberg’s production design, and the editing by Ostlund and Jacob Secher Schulsinger enhances the director’s clinical approach to the material, while furious bursts from Vivaldi’s “Four Seasons” (the “Winter” concerto, of course) are cannily used to punctuate the long silences. The care taken in portraying the avalanche sequence should also be noted; the impact is pretty awesome.

The cool deliberation of “Force majeure” takes a degree of patience to appreciate, and some may find its abrupt tonal shifts bewildering. But it’s a remarkable portrait of a family on the verge.