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Southern California rivers discharge hyperpycnal (river density greater than ocean density) concentrations of suspended sediment (>40 g/L, according to buoyancy theory) during flood events, mostly during El Nino-Southern Oscillation (ENSO) conditions. Because hyperpycnal river discharge commonly occurs during brief periods (hours to occasionally days), mean daily flow statistics often do not reveal the magnitude of these events. Hyperpycnal events are particularly important in rivers draining the Transverse Range and account for 75% of the cumulative sediment load discharged by the Santa Clara River over the past 50 yr. These events are highly pulsed, totaling only ~30 days (~0.15% of the total 50 yr period). Observations of the fate of sediment discharge, although rare, are consistent with hyperpycnai river dynamics and the high likelihood of turbidity currents during these events. We suggest that much of the sediment load initially bypasses the littoral circulation cells and is directly deposited on the adjacent continental shelf, thus potentially representing a loss of immediate beach sand supply. During particularly exceptional events (>100 yr recurrence intervals), flood underflows may extend past the shelf and escape to offshore basins. Keywords: hyperpycnal, suspended sediment, river plume, southern California, Transverse Range.

High-resolution seismic profiles and submersible observations along the leeward slope of western Great Bahama Bank show large-scale export of bank-top sediment and rapid progradation of the slope during the Holocene. A wedge-shaped sequence, up to 90 m thick, is present along most of the slope and consists of predominantly aragonite mud derived from the bank since flooding of the platform 6-8 ka. Total sediment volume of the slope sequence is 40%-80% that of Holocene sediment currently retained on the bank. Maximum rates of vertical accumulation and lateral progradation are 11-15 m/ka and 80-110 m/ka, respectively: 10 to 100 times greater than previously known for periplatform muds. Slope deposition of exported mud during sea-level highs appears to have been a major mechanism for the westward progradation of Great Bahama Bank throughout the Quaternary; this may provide a critical modern analogue for ancient progradational margins.

Writer Mary Sears died at the age of 92 in Woods Hole, MA, on Sep 2, 1997. She devoted the best years of her life as an editor to two oceanographic journals namely, 'Deep Sea Research' where her tenure lasted for 21 years and 'Progress in Oceanography' where she worked for 5 years. Before working as an editor, Sears was affiliated with the US Naval Hydrographic Office where she became an influential force behind the establishment of the office's Oceanographic Unit.