Björk's ability to translate her wildest flights of fancy into magnificent pop has allowed her to stake out territory in almost every existing genre, and to invent a few of her own. On Volta she collaborates with the R'n'B producer Timbaland, the Congolese percussionists Konono No 1, the Chinese pipa player Min Xiao-Fen, the indie darling Antony Hegarty, the noise drummer Brian Chippendale and an all-female Icelandic brass ten-piece, among others. It's a list that smacks of an artist trying a little too hard to live up to her reputation.
Yet she emerges triumphant once again. Volta zigzags between intimate ballads, chopped-up hip-hop beats and stately lovers' duets. Lyrically it is Björk's most outward-looking album: in "I See Who You Are" and "My Juvenile" she sings tenderly about her children, but elsewhere she is in an uncharacteristically political mood. This is never heavy-handed - her musings about suicide bombers on "Hope" are vague and irresolute - but the new-found angle makes for some thrilling pop moments. "Declare Independence" is dedicated to the Faroe Islands and Greenland, with a visceral hiss of "Damn colonists!" midway through. "Earth Intruders" is inspired by the Indian Ocean tsunami of 2004 and the quickening effects of climate change, but Björk's sound picture of the apocalypse sounds more like a wild party than the end of the world.
Despite its twists and turns, Volta never loses its focus. Partly, this is due to Björk keeping those collaborators firmly in their place - for all the big names, none is allowed to stamp its authority too heavily on its contributions. Ultimately, though, it is her artistic restlessness that makes Volta a coherent statement. Its disparate songs are linked by Björk's continually questing approach to her own music.