The five active chimneys of Loki's Castle are venting water as hot as 300 °C (570 °F) and sit on a vast mound of sulfide minerals which is about 825 ft (250 m) in diameter at its base, and some 300 feet (90 m) across its top.[1] A member of the 2008 expedition, oceanographer Marvin Lilley has speculated that this may be the largest such deposit ever seen on the sea floor.[1] The active chimneys are mostly black in colour, but are covered with mats of white bacteria which are living on minerals and materials emitted by the vents.