Geology of the Kodiak Shelf,Alaska: environmental considerations for resource development

Geologic features and processes pose several environmental concerns to resource development on the Kodiak Shelf in the Gulf of Alaska. Tectonism causes fault movement, strong seismic ground shaking, and changes in sea-floor elevation. Earthquake epicenters and structural deformation are areally concentrated, which implies areal variation in the severity of tectonic hazards. Exposures of bedrock appear to provide competent foundational material over broad areas of the sea floor, although locally rough topographic expression of inclined bedrock strata might influence the siting of engineering structures. Stable deposits of gravelly unconsolidated sediment, derived from Pleistocene glaciers, are also widespread. Deposits of fine-grained sediment in areas of negative relief might possess less desirable foundational properties than bedrock or coarse unconsolidated sediment, but their thickness is only a few tens of meters in most places. Evidence of sediment slides is rare on the shelf, which implies general slope stability, but large slides, whose activity is related to tectonism, are abundant just seaward of the shelf break. Local occurrences of gas-charged sediment show limited indication of overpressuring and no evidence of instability, but low sediment strength is possible. Fields of large sand waves might be sites of high-energy bed-load transport with the potential for erosion and abrasion problems. As inferred from sediment dispersal patterns, pollutants that become incorporated into bottom sediment could be concentrated and stored long-term in troughs that trend transversely across the shelf.