Modeling the transport and dispersion of volcanic co‐PDC ash clouds using NAME: an evaluation of source geometry and mass eruption rate

Pyroclastic density currents (PDCs) are gravity currents that frequently form during explosive volcanic eruptions. These ground-hugging density currents consist of high-temperature mixtures of pyroclasts (e.g., ash, pumice), lithics, and gas. They have the potential to generate co-PDC plumes, which detach from the underlying PDC as they buoyantly rise into the atmosphere. Co-PDC plumes, composed of fine-grained ash particles and hot gas, can reach heights of tens of kilometers, potentially dispersing large volumes of ash over continental scale areas, impacting the environment, and posing a risk to aviation. Owing to their formation mechanism, co-PDCs have unique characteristics, such as fine particle sizes (e.g., <90 μm) and a high-aspect ratio, irregular-shaped, source geometry. Here, we consider how the release of ash into the atmosphere from a co-PDC plume may differ to that from a typical Plinian eruption column, and the implications for operational modeling of the resulting ash cloud for the provision of advice to the aviation industry. We use the Numerical Atmospheric-Dispersion Modelling Environment (NAME), which is used by the London Volcanic Ash Advisory Centre. We performed a sensitivity analysis to determine which co-PDC source parameters are important for modeling the associated ash clouds. We show that variations in the source geometry, that is, the total area and aspect ratio, have a minor impact after the first ∼6 hr in the atmosphere.