Orca Inlet - Geology and Currents

Geology and Currents

Like other arms of Prince William Sound, Orca Inlet is a fjord. There are large areas on its coast with large rounded rocks as well as many cirques and hanging valleys. Glacial erosion created steep walls on the sides of the fjord. In one area the elevation rises to 1,600 feet (490 m) within 1⁄₂ miles (0.80 km) of the coastline. The southern and central areas are filled with sediment making the area very shallow. These deposits resulted from the receded glacier that once filled the fjord as well as current inflow through the seaward end of the inlet from the Copper River and other smaller glacial streams. These deposits drift westward along the coast until they reach the entrance of Orca Inlet. Orca Inlet can serve as an entrance to Prince William Sound from the Gulf of Alaska but the shallow water limits the size of vessels that can use the route. In 1914, the southern 2⁄₃rds of the inlet was generally 12 feet (3.7 m) deep or less with a few, discontinuous channels, while the north part was 90 to 228 feet (27 to 69 m) deep.

Copper ore has been found in the area around Orca Inlet but there has been little development to mine it.

The tidal current flows southward on the flood and northward on the ebb. Mean velocity at the peak of the flood is 1.5 knots (2.8 km/h; 1.7 mph) and 0.8 knots (1.5 km/h; 0.92 mph) at the peak of the ebb.