Of all the seedlings that have travelled so far from the original black metal undergrowth in Northern Europe, it is those that have sprouted in North America that have grown into the most unrecognisable new species. At the risk of over-extending the metaphor, perhaps this is a consequence of those seeds taking root in a different cultural or ideological environment. In the Pacific Northwest, we find the same introspection, the same anti-modern nature-worship, but filtered through the lens of a locally grown eco-communalism which re-colours Nietzschean misanthropy in the soft green light of egalitarian positivity.

On other occasions such unexpected offspring can be the result of prolonged intermingling with other, already impure, life-forms. Krallice’s austere and alien music is the mesmerising consequence of black metal dabbling by members of Bloody Panda, Behold… The Arctopus and Dysrhythmia; wildly different again and even further removed from its ancestry. And it is this process of depurification that brings us to Castevet, who drag black metal into a perplexing fusion alongside grooving hardcore and techy death metal. Profound Lore label mates (and fellow NYC scenesters) with Colin Marston’s band, Krallice is surely the single biggest reference point here. But the artwork and title may betray some commonalities with the Cascadian scene as well, predominantly aesthetic but perhaps also in the post-rock influences that penetrate the band's sound deeply. Add to this the hardcore-styled vocals and member backgrounds in brutal death and grind acts, and the gene pool has been so defiled that the use of the term “black metal” to describe Mounds of Ash becomes very problematic.

Undeniably, then, this is a distinctive sound, hewn confidently and precisely from divergent source materials. But, unsurprisingly given the distant common ancestry of these sources, this is less a jolting fusion and more a polished reformulation of an old extreme metal train of thought. Not so much a lurid clash of colours but cleverly blended dark shades. The title track sets up a clunking, bass-heavy post-rock groove, replete with typical time shifts and jangling lead guitar. But this is tormented by the interjections of the kind of tight, rapidfire tremolo that are familiar from records like Dimensional Bleedthrough. They take shape and evaporate, threatening to ignite the track in art-black flames. This is a sound on a knife-edge, flicking restlessly but fluently from one language to another, and it is this intangibility that leads to the album’s subtle high-points. The climactic high-point of Red Star Sans Chastity sees a melodious blackened riff become the focal point for a thumping bass groove and a crescendoing wall of artsy fuzz.

Maybe this fluency is Castevet’s weakness as well as their strength. They use such complex and restless arrangements that it feels like everything has to be tightly leashed to remain under control; attack dogs kicked into shape and forced to work in precise concert. This leaves little room for the kind of screaming, raw, cathartic intensity that characterises much of the best black metal. And conversely, nor does it permit the breathing space for the melodicism of Cascadian bands like Petrychor of the incomparable Skagos to emerge. In creating such an impressive whole, it suffers from the lack of individual moments that really stick in the mind long after the record has been turned off. Castevet rein in the heart to produce ingenious and inventive music for the head.