Two-layer aerated granular flows and implications for pyroclastic density current structure

Two-layer gas-particle currents are investigated using heated (~70 °C) aerating powder (sub-45 micron diameter silica beads) in a flume with a porous base (Figure 1). These flows provide a unique method for observing the interface between a dense granular underflow and a turbulent dilute over-lying flow, as envisaged to exist within many pyroclastic density currents (PDCs), with the aeration effective in overcoming scaling issues related to rapid pore pressure diffusion in thin flows under laboratory conditions (Rowley et al. 2014). Sediment supply from a hopper enables sustained currents to form. High speed video at 1024 x 256 pixels is used to record the flow behaviour through a transparent perspex sidewall.