A variety of deformation structures in sandy sediments are described, the origin of which may be ascribed to the escape of excess pore‐water from liquefied and fluidized sediments in response to density instabilities created by external and/or internal loading. A number of deformations found in exposed nearshore sediments of an artificially drained lake provide an explanatory model according to which rapid drops in water level during the development of waterway systems in connection with post‐glacial land uplift are suggested in many cases to have served as creational environments for soft sediment deformation. Other favourable circumstances in glaciated areas were obviously offered by the complex melting and sedimentation mechanisms which occurred in the envionment of the retreating ice‐m