Welded Breakdown

Breakdown may occur before or after a tube has drained and cooled. When it occurs during the cooling phase, breakdown falling onto a partially cooled floor may by welded to it by “segregations,” material boiling out of the semi-solid floor matrix. Breakdown may also occur after a tube has cooled, but then be overflowed by a subsequent lava flow that  forms a coating and “welds” it together or on to the floor. This is likely the mechanism for the coated pile of rocks in the second photo

Breakdown may also be moved downflow with the stream of lava before being emplaced, especially if its specific gravity is less than the molten lava on which it floats. As it moves, it may roll along and accumulate molten lava, becoming a lava ball.