Augustine Volcano is a stratovolcano in Alaska consisting of a central complex of summit lava domes and flows surrounded by an apron of pyroclastic, lahar, avalanche, and ash deposits. The volcano is frequently active, with major eruptions recorded in 1883, 1935, 1963–64, 1976, 1986, and 2006. Minor eruptive events were reported in 1812, 1885, 1908, 1944, and 1971. The large eruptions are characterized by an explosive onset followed by the quieter effusion of lava. It forms Augustine Island in southwestern Cook Inlet in the Kenai Peninsula Borough of southcentral coastal Alaska, 174 miles (280 km) southwest of Anchorage. Augustine Island has a land area of 32.4 square miles (83.9 km2), while West Island, just off Augustine's western shores, has 2 sq mi (5.2 km2). The irregular coastline of Augustine Island is due to the repeated catastrophic collapse of the summit dome, forming debris avalanches down the flanks and into Cook Inlet.

Cook Inlet stretches 180 miles (290 km) from the Gulf of Alaska to Anchorage in south-central Alaska. Cook Inlet branches into the Knik Arm and Turnagain Arm at its northern end, almost surrounding Anchorage. On its southern end, it merges with Shelikof Strait, Stevenson Entrance, Kennedy Entrance and Chugach Passage.