Volcanic Unrest at Taupō Volcano in 2019: Causes, Mechanisms and Implications

Taupō volcano, New Zealand, is a large caldera volcano that has been highly active through the Holocene. It most recently erupted ∼1,800 years ago but there have been multiple periods of historic volcanic unrest. We use seismological and geodetic analysis to show that in 2019 Taupō underwent a period of unrest characterized by increased seismic activity through multiple swarms and was accompanied by ground deformation within the caldera. The earthquakes, which include non‐double‐couple events, serve to outline an aseismic zone beneath the most recent eruptive vents. This aseismic zone is coincident with an inflating source, based on forward modeling of ground deformation data. We infer that this aseismic and deforming region delineates the location of the present day magma reservoir that is ≥250 km3 in volume and has a melt fraction of >20%–30%, inhibiting seismic activity. Our analysis shows that the 2019 unrest at Taupō was volcanic in nature and origin, demonstrating that this is an active and potentially hazardous volcano, and that improving our monitoring and understanding of its behavior is important. Plain Language Summary Taupō in New Zealand, is a large caldera volcano which has been very active in recent geological time, but has not erupted for about 1,800 years. However, in historical times it has undergone periods of unrest involving abundant, sometimes damaging earthquakes, and ground deformation, but no eruption. In 2019, Taupō volcano underwent one of these unrest periods, represented by a large increase in the number of earthquakes and observable ground deformation within the caldera. Using the locations and patterns of the earthquakes and ground deformation allow us to infer that beneath the caldera there is an active magma reservoir of at least 250 km3 volume and which is at least 20%–30% molten. New magma being fed into this reservoir caused the triggering of earthquakes in the surrounding brittle crust along fault lines that reflect both the volcano structure and the regional rift faults that cut across the volcano. Our findings show that Taupō needs to be carefully monitored to better understand the processes at depth and the factors that might cause similar unrest to escalate into an eruption in the future. Key Points In 2019 Taupō volcano underwent a period of volcanic unrest, indicated by multiple seismic swarms and ground deformation Earthquakes define a brittle‐ductile transition around an aseismic zone that is coincident with an