Lava breakouts are flows that reach the surface through a skylight or crack in a lava tube. This informal term is useful at Kilauea, where such flows are common. Breakouts more often form when the tube is actually blocked by a dam. Breakouts since September 23 have resulted from dams within the tube. The roof and walls of the tube cooled when the tube emptied following the intrusion on September 12.
Rocks shrink and crack when they cool, spalling off the sides of the tube.
Consequently piles of rocks formed at a number of places in the tube. When lava again entered the tube, it had to spill onto the surface upstream of a strong dam, forming breakouts. Small flows spill out from the pond, building the banks of the pond higher. As a result, the surface of the pond can rise, spill out again, and rise once more. Perched ponds formed at several places where breakouts took place since September 23.