Heat Transfer in Pyroclastic Density Current-Ice Interactions: Insights from Experimental and Numerical Simulations
Stratovolcanoes are common globally, with high altitude summit regions that are often glacier-clad and intersect the seasonal and perennial snow line. Explosive eruptions from stratovolcanoes can generate pyroclastic density currents (PDCs). When PDCs are emplaced onto and propagate over glacierised substrates, melt and steam are generated and incorporated into the flow, which can cause a transformation from hot, dry granular flow, to a water-saturated, sediment-laden flow, termed a lahar. Both PDCs and ice-melt lahars are highly hazardous due to their high energy during flow and long runout distances. Knowledge of the physics that underpin these interactions and the transformation to ice-melt lahar is extremely limited, preventing accurate descriptions within hazard models. To physically constrain the thermal interactions we conduct static melting experiments, where a hot granular layer was emplaced onto an ice substrate. The rate of heat transfer through the particle layer, melt and steam generation were quantified. Experiments revealed systematic increases in melt and steam with increasing particle layer thicknesses and temperatures. We also present a one-dimensional numerical model for heat transfer, calibrated against experiment data, capable of accurately predicting temperature and associated melting. Furthermore, we present similarity solutions for early-time melting which are used to benchmark our numerical scheme, and to provide rapid estimates for meltwater flux hydrographs. These data are vital for predicting melt volume and incorporation into PDCs required to facilitate the transformation to and evolution of ice-melt lahars.