Studies to date on continental slope deposits of Peru and Oregon indicate that coastal upwelling indirectly contributes to the alteration of sediment mass physical properties and stability characteristics by concentrating organic matter in the underlying and nearby sediments. Those sediments in close proximity to areas of intense upwelling display distinctly different geotechnical properties than do those of comparable sediment type some distance away. The ability of organic matter to adsorb water and to aggregate clay-size particles to form an open fabric appears to result in exceptionally high water

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content (853% by dry weight), porosity (89%), and plasticity as well as very low bulk density (1.09 Mg/m³). The undrained shear strength (cohesion) of these sediments is also unexpectedly high, resulting apparently from some form of bonding of the sediment particles by organic matter. Sensitivity (ratio of natural to remolded or disturbed shear strength) is also unusually high (21), indicating a high susceptibility to failure if the sediments should become severely disturbed. All sediments along the margins behave as if they are overconsolidated. The greater the organic content the greater the degree of overconsolidation. In some areas this degree is on the order of six to seven times that of similar slope deposits but with relatively low organic contents. This degree of ov rconsolidation suggests that organic-matter related, interparticle bonding may be responsible for the apparent overconsolidation.

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