Since the beginning of this volcanic crisis the physical and chemical parameters of waters and fumarolic gases from Terceira Island have been monitored, with no changes detected. Another submarine eruption took place in this general location in June 1867. At that time five months of strong seismicity destroyed about 200 houses at Serreta. Historically active Santa Barbara volcano at the western end of the island is truncated by two calderas. The youngest of these formed about 15,000 years ago.
Comenditic lava domes fill and surround the caldera.
Pico Alto lies north of the fissure zone in the north-central part of the island and contains a Pleistocene caldera largely filled by lava domes and lava flows. Historical eruptions have occurred from Pico Alto, the fissure zone between Pico Alto and Santa Barbara, and from submarine vents west of Santa Barbara.