| dc.description.abstract | Simpson Bay is a turbid, outwash fjord located in northeastern Prince William Sound, Alaska. A
high ratio of watershead:basin surface area combined with high precipitation and an easily erodable
catchment create high sediment inputs. Fresh water from heavy precipitation and meltwater from high
alpine glaciers enter Simpson Bay through bay head rivers and small shoreline creeks that drain the
catchment. Side scan sonar, seismic profiling, and high resolution bathymetry were used to investigate the
record of modern sedimentary processes. Four bottom types and two seismic faces were described to
delineate the distribution of sediment types and sedimentary processes in Simpson Bay. Sonar images
showed areas of high backscatter (coarse grain sediment, bedrock outcrops and shorelines) in shallow
areas and areas of low backscatter (estuarine mud) in deeper areas. Seismic profiles showed that high
backscatter areas reflected emergent glacial surfaces while low backscatter areas indicated modern
estuarine mud deposition. The data show terminal morainal bank systems and grounding line deposits at
the mouth of the bay and rocky promontories, relict medial moraines, that extend as terrestrial features
through the subtidal and into deeper waters. Tidal currents and mass wasting are the major influences on
sediment distribution. Hydrographic data showed high spatial variability in surface and bottom currents
throughout the bay. Bottom currents are tide dominated, and are generally weak (5-20 cm s-1) in the open
water portions of the bay while faster currents are found associated with shorelines, outcrops, and
restrictive sills. Tidal currents alone are not enough to cause the lack of estuarine mud deposition in
shallow areas. Bathymetric data showed steep slopes throughout the bay suggesting sediment gravity
flows. Central Alaska is a seismically active area, and earthquakes are most likely the triggering
mechanism of the gravity flows. | en |
