The submarine topography of lower Cook Inlet, Alaska, is complex because the bathymetric aspects and water depths change rapidly over short distances. The folded upper Tertiary subbottom was eroded during the first of five major Quaternary glacial advances over the inlet, and later fluvial, fluvioglacial, glacial, and marine erosional and depositional processes shaped the bottom to its present configuration.
Most of lower Cook Inlet has a relative smooth topography showing small local highs and lows, and slopes with gradients generally ranging from less than a degree to locally about 5°. Around the southwestern Kenai Peninsula and the Barren and Kodiak Islands, strong faulting with vertical movement has added to the complexity of bottom topography. Less complex, nonfaulted areas occur near Kalgin Island and south Kachemak Bay and around Augustine Island.
To facilitate description of lower Cook Inlet the estuarine body is divided into three large regions, northern and central, southern, and eastern; and these regions are divided into smaller physiographic areas on the basis of submarine topographic characteristics and 20-m depth zonations. Each area is named by combining the geographic name of a nearby place or feature on land with a common term for a marine physiographic feature -- trough, platform, ramp, slope, plateau. Local highs and deeps having lees than 5-m relief, which can be important to fisheries and specific research or economic studies, are not named, mentioned in text, or shown on the figures.
