Agua de Pau

Geography & Climate

Agua de Pau is located in Portugal, within the Azores-Terceira Rift Volcanic Province of the broader Atlantic Ocean Volcanic Regions. Situated at 37.77° N, 25.47° W in the Northern Hemisphere, the volcano lies within a temperate climate zone. With a summit elevation of 947 meters above sea level, Agua de Pau is a moderately sized peak that remains accessible to hikers and researchers for much of the year. The volcanic landform is characterized as a composite, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Agua de Pau is situated along a rift zone, where tectonic plates are pulling apart. As the crust thins and fractures, magma rises to fill the gap, creating volcanic activity. Rift volcanism typically produces more fluid lava flows rather than explosive blasts, which means communities near Agua de Pau in Portugal generally face slower-moving hazards like lava flows and ground fissures rather than sudden pyroclastic events. However, rift volcanoes can still generate significant ash emissions and gas releases that affect local air quality. The dominant rock type is trachyte / trachydacite, an intermediate to silica-rich volcanic rock. This composition typically produces more viscous magma, leading to more explosive eruptions with ash columns and pyroclastic flows. Andesitic and dacitic magmas build pressure before erupting, which is why volcanoes with this rock chemistry are often associated with Plinian-style eruptions that can send ash tens of kilometers into the atmosphere and disrupt aviation across entire regions.

Eruption History Summary

Agua de Pau has 10 recorded eruptions in the geological database, spanning from 6750 BCE to 1564 CE. The most powerful recorded event was a paroxysmal eruption with devastating regional consequences in 1563 CE, reaching VEI 5 on the Volcanic Explosivity Index. Notable eruptions include 1563 CE (VEI 5), 1290 BCE (VEI 4), 1850 BCE (VEI 3). This level of eruptive frequency indicates a persistently active volcanic system that warrants ongoing monitoring.

Significance

With a maximum recorded VEI of 5, Agua de Pau has demonstrated the capacity for paroxysmal eruptions comparable to the 1980 eruption of Mount St. Helens. Eruptions of this scale can devastate areas within 20-30 kilometers and produce ash fall that disrupts aviation and agriculture across hundreds of kilometers. With 10 recorded eruptions, Agua de Pau has a substantial eruptive history that provides valuable data for understanding volcanic behavior and assessing future hazards in the Atlantic Ocean Volcanic Regions region.

GVP Reference Summary

The Agua de Pau stratovolcano in central Sao Miguel Island contains an outer 4 x 7 km caldera formed about 30,000-45,000 years ago and an inner 2.5 x 3 km caldera that was created about 15,000 years ago. The younger caldera is partially filled by the Lagoa do Fogo caldera lake. Several post-caldera lava domes were emplaced on the northern and western flanks, but activity in the caldera did not resume until about 5000 years ago. The 3 km3 Fogo-A plinian pumice fall deposit was emplaced at this time. Numerous flank cinder cones mark radial and concentric fissures, some of which have been active during historical time. The latest trachytic explosive eruption took place during 1563. Prominent hot springs are located on the NW flank.

— Smithsonian Institution, Global Volcanism Program