Strongly gliding harmonic tremor during the 2009 eruption of Redoubt Volcano

► Upward gliding harmonic tremor occurred prior to consecutive Vulcanian explosions. ► Fundamental frequency of tremor approaches 30 Hz, followed by aseismic pause. ► High frequency tremor returned during extrusive phase. ► We believe this tremor is composed of repeating stick-slip earthquakes near conduit.