The lava column at Halemaumau consists of a main semisolid incandescent body (bench magma), perforated by small shafts leading to a saucer on its summit, which contains a shallow lake of liquid lava. The bench magma grades by decreasing viscosity upward into the lava lake and downward into a more fluid part of the magma column. The top of the bench magma is constantly being added to by overflows from the lava lake and accumulation of foundered crusts. Loading of part of its surface by overflow results in isostatic sinking of that part and a compensating rise of some other part, the latter often producing islands of bench magma in the lava lake. During subsidence, the lake magma sinks more rapidly than the bench magma, leaving the islands of bench magma standing higher than before subsidence took place. The process of island formation is well-illustrated by photo sequences. Jaggar reviews the earlier contributions of Brun, Daly, Perret, Day and Shepherd, and Green on the nature of magmatic gases and describes the flames produced by burning gases.