Tsunami Warning Protocol for Eruptions of Augustine Volcano, Cook Inlet, Alaska

Augustine is an island volcano that has generated at least one tsunami. During its January 2006 eruption coastal residents of lower Cook Inlet became concerned about tsunami potential. To address this concern, NOAA's West Coast/ Alaska Tsunami Warning Center (WC/ATWC) and the Alaska Volcano Observatory (AVO) jointly developed a tsunami warning protocol for the most likely scenario for tsunami generation at Augustine: a debris avalanche into the Cook Inlet. Tsunami modeling indicates that a wave generated at Augustine volcano could reach coastal communities in approximately 55 minutes. If a shallow seismic event with magnitude greater than 4.5 occurred near Augustine and the AVO had set the level of concern color code to orange or red, the WC/ATWC would immediately issue a warning for the lower Cook Inlet. Given the short tsunami travel times involved, potentially affected communities would be provided as much lead time as possible. Large debris avalanches that could trigger a tsunami in lower Cook Inlet are expected to be accompanied by a strong seismic signal. Seismograms produced by these debris avalanches have unique spectral characteristics. After issuing a warning, the WC/ATWC would compare the observed waveform with known debris avalanches, and would consult with AVO to further evaluate the event using AVO's on-island networks (web cameras, seismic network, etc) to refine or cancel the warning. After the 2006 eruptive phase ended, WC/ATWC, with support from AVO and the University of Alaska Tsunami Warning and Environmental Observatory for Alaska program (TWEAK), developed and installed "splash-gauges" which will provide confirmation of tsunami generation.