The singular presence of volcanic blisters characterizes some areas in the north of the San Pietro island. These structures involve outcrops of Serra di Paringianu rhyolite in La Punta's locality. They were described for the first time about ninety years ago by Michele Taricco. Blisters are also present in Monte Ulmus hyperalkaline rhyolites, whose identification between the Canale di Memerosso and Punta Regolina is much more recent.

These singular volcanic structures consist of collapsed blisters, generally hemispherical, with a diameter ranging from 1 to 3 m for those of Punta Regolina up to 10 m and more for La Punta have been produced following processes of degassing of pyroclastic-flow deposits during their emplacement.

In effusive basaltic eruptions, blister-type structures are quite frequent. Their presence in ignimbrite deposits is considered an absolute world rarity, as in Ethiopia's Fantale volcano.