The channel is navigable by large ships, only from the southeast, as far as the
Douglas Bridge, approximately . Between the bridge and
Juneau International Airport, approximately , it is navigable only by smaller craft and only at high tide. The channel is becoming increasingly unnavigable due to shallow water depths. The two principal causes for this are: •
Isostatic rebound following the retreat of glacial ice sheets • Sedimentation and infilling of the Gastineau Channel by silty sediment produced by the
Mendenhall Glacier and
Mendenhall River. If current trends continue, Gastineau Channel may eventually become dry or unnavigable or both. During
isostatic rebound, the Earth's
lithosphere (crust) is slowly rising because of buoyant forces, following the removal of a large mass on the surface. This can be likened to an ice cube floating in a glass of water with a penny sitting on top. The weight of the penny makes the ice cube float lower, similar to the immense weight of a glacier on top of the lithosphere. When the penny (glacier) is removed, the ice cube (lithosphere) "rebounds" and floats slightly higher. In the geologic case, that scenario happens very slowly. Rates of isostatic rebound throughout SE Alaska vary from 0.1 to 1.5 inches/year depending on glacial history. The approximate rebound rate in the Juneau area is 0.25 to 0.5 inches/year. ==References==