Semisopochnoi is monitored with an on-island seismic network and remotely by satellite and lightning sensors. An infrasound array on Adak Island may detect explosive emissions from Semisopochnoi with a slight delay (approximately 13 minutes) if atmospheric conditions permit.
Aug 11, 2019 17:51 – Seismicity remains slightly above background with occasional discrete low-frequency earthquakes and low-level tremor. No activity observed in satellite data. It remains possible for unrest to escalate rapidly with little to no warning.