Hydrothermal vent at Brimstone Pit at NW Rota-1 volcano, Rota, Mariana Islands. A degassing event at a hydrothermal vent, releasing bubbles (probably carbon dioxide). NW Rota-1 is a seamount in the Mariana Islands area. It has several craters, the most active of which is called Brimstone Pit. The yellow parts of the plume in the background contain tiny droplets of molten sulphur. The hydrothermal activity nourishes microbial mats and many animals, although the unstable environment from the frequent eruptions limits animal diversity.