Meteorologists describe the life cycle in stages. Warm water heats the air immediately above it, and where surface winds converge and shear, that rising column begins to rotate. The first visible sign is a dark spot on the water, marking the low-pressure core of the young vortex. As buoyant air is stretched vertically beneath the cloud, conservation of angular momentum spins it faster - the same reason a skater speeds up on pulling in the arms - and the falling pressure inside the core cools the air enough for its moisture to condense, producing the visible funnel that appears to link cloud and river. A ring of churning spray, called the cascade, forms where the vortex meets the water. Landfall ends it: friction slows the rotation and the vortex loses the warm, moist surface that fed it, so the funnel disorganises within minutes. The vital point for exams is what the funnel is made of - condensed vapour formed in situ by the pressure drop, not river or sea water drawn up the column.