The outer caldera dates from between 30,000 and 45,000 years ago, and comprises an area 4km wide and 13km long outer caldera (corresponding to the Água de Pau Massif) [REF].
Owing to the existence of hot springs along the northwest flank, particular in the so name Caldeiras da Ribeira Grande and Caldeira Velha, the region has been used in the generation of geothermal energy or as therapeutic tourist spas [REF].