Pululahua dome complex, Ecuador: eruptive history, total magma output and potential hazards

International audiencePululahua is a potentially active dome complex located 15 km north of Quito. It is composed of sixteen dacitic-andesitic lava domes located inside and around a semi-rectangular depression. We divide its eruptive history into: (1) a first member characterized by effusive lava dome growth and collapse (Units I and II, >18-12 ka), (2) a second member consisting of at least four explosive eruptive phases (VEI ~4), responsible for the formation of a caldera-like depression (Unit III, 2.6-2.3 ka cal BP), and (3) a final member encompassing partially explosive dome growth inside the depression (Unit IV, 2.2 ka cal BP). Rock samples show no significant geochemical changes over time, except for a slight decrease in SiO2 and a minor increase in MgO and Fe2O3 towards younger magmas. In addition, based on field measurements, a total minimum bulk volume of all domes and pyroclastic deposits is estimated at ~5.75 ± 0.14 km³, yielding a dense rock equivalent of ~4.24 ± 0.1 km³ and a total erupted magma mass of 10.58 ± 0.16 E+12 kg. Finally, we put forward three future hazard scenarios that could affect the population in the proximal area (>70 k people): (1) an unrest period involving increased seismic events, volcanic gas emissions and potentially small phreatic explosions, (2) the effusive and/or slightly explosive growth and destruction of lava domes accompanied by block-and-ash flows and tephra fall, and (3) large explosive events (VEI ~4) that generate regional tephra fall and massive pyroclastic density currents