Nepheloid layer generation by gas eruption:unexpected experimental results

Knowledge of nepheloid layers is important to improve the understanding of physical,geological,and sedimentary processes from continental shelf to abyssal environments.We had not tried to study the nepheloid layers in a hydrate-associated tank until unexpected results occurred.Tank experimental results show that gas eruptions triggered intermediate nepheloid layers.Thus,we proposed a new mechanism of intermediate nepheloid layer generation by eruptions.The intermediate nepheloid layers were generated in uniform-density fluid,which indicated that stratified fluid is not a necessary condition for intermediate nepheloid layers.Sufficient space for advection and an oblique slope for detachment are the key ingredients for intermediate nepheloid layer generation by eruptions.Our experiments also offer a new experimental evidence for bottom nepheloid layer generation by earthquakes.Given the scale effects of laboratory experiment,it is important to determine whether submarine volcanic eruption or hydrate-associated venting causes intermediate nepheloid layer in the nature.

Wave flume experiments on dynamics of the bottom boundary layer in silty seabed

The objectives of this study are carried out a series of controlled large wave flume experiments using fine-grained sediment from the Huanghe River Delta,exploring the complete sequence of sediment behavior in the bottom boundary layer(BBL)during wave-induced liquefaction.The results show that:(1)The BBL in silty seabed is exposed to a progressive wave,goes through a number of different stages including compaction before liquefaction,sediment liquefaction,and compaction after liquefaction,which determines the range and thickness of BBL.(2)With the introduction of waves,first,the sediment surface has settled by an amount S(S=1–2 cm)in the course of wave loadings with an insufficient accumulation of pore water pressure.And a thin high concentration layer formed the near-bed bottom.(3)Once the liquefaction sets in,the liquefied sediment with an‘orbital motion’and the sub-liquefied sediment form a two-layer-sediment region.The range of BBL extends downwards and stopped at a certain depth,subsequently,develops upwards with the compaction process.Meanwhile,resuspended sediments diffuse to the upper water column.(4)During the dynamics process of the BBL beneath progressive waves,the re-suspended sediment increment ranked as sediment liquefaction>erosion before liquefaction>compaction after liquefaction.