What is it about?
When river waters enter the ocean, they typically float buoyantly on the denser sea water, but river outflows containing high concentrations of suspended sediment may plunge where the density of parts of the outflow become greater than seawater. These are energetic areas and there have been few in situ observations of process. This study used data collected by the USGS and NOAA over a period from 1936 to 2001 to document how a channel developed within a deposit of spoilts formed from local dredging. Erosion appears to have occurred by retrogressive retreat of the steep upper part of the channel.
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Why is it important?
The origin of plunging currents in river-mouth locations has been controversial - either they form directly from water of high enough sediment concentration to be negatively buoyant (hyperpycnal flows) or from slope failure and disaggregation of the failed material, forming turbidity currents. Here, a set of fine gullies found on the outer slope (farthest from the river) would not have been produced by a submarine slope failure, so they are morphological evidence for a genuine hyperpycnal current in this location.
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This page is a summary of: Channelled erosion through a marine dump site of dredge spoils at the mouth of the Puyallup River, Washington State, USA, Marine Geology, October 2005, Elsevier,
DOI: 10.1016/j.margeo.2005.06.032.
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