The 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.
The Cook Inlet provides navigable access to the port of Anchorage at the northern end, and to the smaller Homer port further south. Approximately 400,000 people live within the Cook Inlet watershed. Before the growth of Anchorage, Knik was the destination for most marine traffic in upper Cook Inlet.
The Cook Inlet region contains active volcanoes, including Augustine Volcano and Mount Redoubt. Volcanic eruptions in the region have been associated with earthquakes and tsunamis, and debris avalanches have resulted in tsunamis also. There was an earthquake of the magnitude of 7.1 on 31 December 1901 generated by an eruption that caused several tsunamis.