The papules evolved through phases of vesiculation, pustulation, umbilication, and crusting. Weak positives are slightly elevated pink or red plaques, usually with mild vesiculation. The vesiculation initiation and termination is thus recorded in the obsidian sample. The more gradual change of the water content curve represents a longer vesiculation event. Vesiculation, i.e. the nucleation and growth of bubbles commonly initiates eruptions in volcanic domes.