The ninth studio album from Seattle’s drone overlords is something like a companion piece to April’s colossal Life Metal LP. Back then, core members Steve O’Malley and Greg Anderson were joined by the usual assortment of adventurous guests, including Silkworm’s Tim Midyett, synth guy Tos Nieuwenhuizen and composer/cellist Hildur Guðnadòttir (if you’re wondering where you’ve heard that name recently, she did the Chernobyl soundtrack).

Recording sessions took place over two weeks, cut to two-inch tape by Steve Albini, and each day would begin or conclude with a 12-minute group improvisation. You can imagine the purpose of such an exercise: a ritual to align the great but distinct creative energies in the room, or else a chance for collaborators to position themselves inside the dense bedlam of O’Malley and Anderson’s soundworld.

Pyroclasts brings us four of these improvisations. Perhaps they illuminate the process behind one of the year’s most compelling releases, but don’t get the wrong idea; this is not some overcooked extras disc. Rather, it’s a unique and triumphant work that favours harmonic richness over abyssal riffing. Pyroclasts is made of serious slow-burners, even by the band’s glacial standards. All four circle largely around a single chord, building and cooling like the core of a star in flux, radiating fiercely and magnificently.

It’s a step away from the prevalent moods of previous releases: the resolute despair on Flight of the Behemoth, or Attila Csihar’s doom-laden prophecies on Monoliths and Dimensions. On Pyroclasts, Sunn O))) gives us something that sounds like creation itself: joyous, turbulent and enduring.

Xavier Boucherat