Agua de Pau is a stratovolcano in central Sao Miguel Island . About 30,0000 to 45,000 years ago the 4 km wide and 7 km long outer caldera was formed. The inner caldera, which is 2.5 km wide and 4 km long was formed about 15,000 years ago. The younger inner caldera is partially filled by the crater lake Lago de Fogo . Until 5000 years ago the activity in the caldera created several post-caldera lava domes on the northern and western flank. Some of the cinder cones placed on the flank mark radial and concentric fissures. Some of them have been active during historical time. The latest known eruption took place in the year 1563. At the NW flank some popular hot springs are located.

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