Minecraft wiki entry for Bubble_Column, associated text: Upward bubble columns can be identified by the presence of vertically rising air bubbles. An upward bubble column accelerates entities upward. The longer an object rises through the bubble column, the faster it travels. At high enough speeds, players and entities can be launched out of water by several blocks. Sitting on the surface above a rising bubble column causes entities to bounce upward repeatedly by about 1 block.