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Ambient noise interferometry is becoming increasingly popular for studying seismic velocity changes. Such changes contain information on the structural and mechanical properties of Earth systems. Application to monitoring, however, is complicated by the large number of processes capable of inducing crustal velocity changes. We demonstrate this at White Island volcano over a 10-year period containing multiple well-documented eruptions. Using individual seismic stations, we detect velocity perturbations that we ascribe to volcanic activity, large earthquakes, and seasonality. Distant seismic stations capture widespread nonvolcanic changes that are also present at the volcano. Comparison between velocity changes recorded by distant and local stations then allows us to distinguish volcanic phenomena from seasonality. Through this, we resolve distinct features in ambient noise-derived velocity changes that relate to volcanic unrest and a phreatic eruption, illustrating the strength of the approach.

Plain Language Summary Detecting small changes in physical properties at volcanoes is important toward effectively forecasting volcanic eruptions. One approach is to monitor the speed of seismic waves at the Earth's surface, which are sensitive to changes in the rock they pass through. At volcanoes, such changes may manifest through subsurface pressure increases preceding eruptions. Correctly interpreting these changes, however, is complicated. Many other, nonvolcanic, processes are also capable of producing similar wave speed perturbations. At White Island volcano, New Zealand, we detect changes associated with volcanic activity, large earthquakes, and weather-related processes using seismometers located on the volcano. We demonstrate that volcanic and nonvolcanic features can be distinguished by comparing changes recorded at the volcano with those recorded at large distances, where volcanic changes are not expected to be observed. Through this, we resolve distinct differences that can be related to volcanic activity, illustrating the strength of this approach.