The physics of bubbles in surficial, soft, cohesive sediments

This paper reviews current understanding of the physics of bubbles in soft (unlithified), cohesive sediments, certainly in the top 100 m from the sediment–water interface, but likely much deeper.Experimental evidence, primarily CT scans and internal pressure records, indicate that near-surface bubbles grow by elastically compressing and fracturing these sediments, which results in thin, irregular disks of gas. These data do not suggest either plastic or fluid behavior on the part of the bulk sediment. In addition there is no hint of capillary invasion of gas into the pores of fine-grained sediments.The growth rate of an elastic-fracturing, disk-shaped, bubble can vastly exceed that of a spherical bubble, depending on the eccentricity of the bubble. This effect results from the far more favorable surface-to-volume ratio of flattened bubbles. The initial rate of rise of bubbles in cohesive sediments also appears to be governed by a fracture process, which is driven by pseudo-buoyancy. The rate of bubble rise could be controlled by various possible mechanisms, but only the predictions from a visco-elastic-fracture propagation model seem to produce rise velocities that are not ballistic (

► This is a review of the physics of bubbles in soft, cohesive sediment.
► It covers nucleation, growth theories and observations, rise theories and observations, and bubble accumulation.
► It also examines the role of capillarity and sediment geotechnical properties in these phenomena.
► Based on this review, this paper argues that bubble growth in near-surface cohesive sediment occurs by elastic fracture.
► Rise is also likely a visco-elastic fracture process.