Abstract: Littoral Processes and Geomorphic Variability on Storm-Dominated, Glacial Shoreline, Malaspina Foreland, Gulf of Alaska

M. F. Stephen, M. O. Hayes, C. H. Ruby, S. J. Wilson

The shoreline of the Malaspina foreland on the Gulf of Alaska consists of an actively eroding glacial margin with short, steep beaches backed by till and kame scarps. Flanking the eroding glacial margin are active outwash plains, with progradational barrier spits forming beach-ridge plains downdrift of the major river mouths. Prograding spits build into the deeper waters of Icy Bay and Yakutat Bay west and east of the Malaspina foreland.

Regional process parameters document littoral transport in directions that correlate with regional morphology. Dominant south and southeast waves result in sediment transport away from eroding-till cliffs and from the mouths of outwash streams.

Detailed littoral process observations were obtained at two levels during July-August 1975:

A. Process network: regional process variability was determined by multiple observations during stable meteorologic conditions.

B. Six process zonals: 48-hour continuous monitoring of meteorologic, wave, littoral, and morphologic variability at single sites selected as representative of shoreline segments.

Process zonal measurements allowed documentation of the passage of a complete storm cycle. Commonly, two distinct wave trains were monitored. Under such conditions, drift directions and velocities were erratic and strong rip currents were prevalent. Dominant wave approach was a function of the path of low-pressure systems moving through the Gulf of Alaska. Southerly waves were characteristic of calm conditions, and southeasterly waves were characteristic of storms.

Breaker heights averaged 1.5 to 2.0 m, with a maximum measured height of 4 m recorded during a storm. Suspended-sediment concentrations taken from the bore of plunging waves were as high as 150 g/l and averaged 60 g/l. Longshore drift velocities ranged as high as 150 cm/sec. Measured beach profiles revealed as much as 15 cm of accretion to the beach face during one tidal cycle. These field data, in conjunction with wave-hindcast data, wave-energy-flux calculations, and air-photo determinations of spit accretion will be used to compute volumetric transport and dispersal rates.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA