An improved quantitative measure of the tendency for volcanic ash plumes to form in water: implications for the deposition of marine ash beds

摘要: Laboratory experiments and numerical simulations have shown that volcanic ash particles immersed in water can either settle slowly individually, or rapidly collectively as particle-laden plumes. The ratio of timescales for individual collective settling, the form analytical expressions, provides a dimensionless quantitative measure tendency such plumes to grow persist which has important implications determining particle residence times deposition rates. However, existing measures literature assume settling obeys Stokes' law is therefore controlled by balance between gravitational forces viscous drag, despite plume development actually being inertial drag even absence turbulence during early times. This paper presents new onset takes into account drag-controlled (rather than drag-controlled) nature growth descent. A parameter study comprising set small-scale highlights effectiveness and, comparison with an literature, also demonstrates timescale grossly under-estimated when assuming slowed drag. Furthermore, formulation means be estimated from thickness concentration final deposit; magnitude duration flux across water's surface do not need known. permits large body more accurately practically determined, allows improved interpretation layers volcaniclastic material deposited at seabed.