Shaded-Relief Image of San Francisco Bay

[San Francisco Shaded Relief Image]

The bathymetry maps of west-central San Francisco Bay were gridded at4-m pixel resolution.

Prominent features on the bathymetric map include:

  • a large sediment drift against the west side of Alcatraz Island
  • bathymetric depressions on the south sides of Alcatraz and Angel Islands and at the Golden Gate
  • bedrock highs in the middle of the bay

Much of the surface of central San Francisco Bay is ornamented with atleast three scales of sand waves, the largest class having wavelengths of>40 m and wave heights of >5 m. These bedforms reflect the strongdiurnal tidal cycles that occur in the bay. The large bedform field immediatelywest of Alcatraz Island appears to be a sediment drift, similar to a hugesand dune, with smaller bedforms on its surface. The bedforms around theTiburon Peninsula show the effects on the sea floor of strong tidal flowaround the land.

A large hole has been excavated just off the southwest edge of AlcatrazIsland, apparently related to the outgoing ebb tide that flows around thesouth end of the island.

The rock outcrops to the northwest of Alcatraz Island are clearly shownand their heights have been determined within 30 cm and their volumes havebeen calculated.

The shaded-relief image of the land surrounding San Francisco Bay wasconstructed using a DEM (Digital Elevation Model) with 10-meter resolutionprovided by the USGS National Mapping Division.


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