  Volcanic ash clouds often become multilayered and thin with distance from the
vent. We explore one mechanism for development of this layered structure. We
review data on the characteristics of turbulence layering in the free
atmosphere, as well as examples of observations of layered clouds both
near-vent and distally. We then explore and contrast the output of volcanic ash
transport and dispersal models with models that explicitly use the observed
layered structure of atmospheric turbulence. The results suggest that the
alternation of turbulent and quiescent atmospheric layers provides one
mechanism for development of multilayered ash clouds by modulating the manner
in which settling occurs.
