The role of discharge history on Strombolian-plume rise

The motion of Strombolian volcanic plumes is often treated as a volcanic thermal, sensitive to the total amount of material discharged during an eruption rather than the discharge rate or its fluctuations. However, observations suggest that the discharge rate varies over the duration of a Strombolian eruption possibly subjecting Strombolian ash plumes to strong and sudden changes in dynamics midrise. Experimental work by Chojnicki (2012, PhD, ASU) suggests that eruptions with a Gaussian-like discharge history generate plumes that rise with a logarithmic dependence on time. Though a Gaussian-like discharge history may reasonably approximate some Strombolian events, it is difficult to understand whether it represents a few events or many of them. Consequently, we are using numerical methods to explore the sensitivity of the rise process to the form of the discharge history. We consider multiple discharge histories and observe the large-scale turbulent structures formed from each condition that govern the rise process and morphology of each flow at early times. The internal velocity configurations in these flows are sensitive to the presence of the large-structures. As mass transport in these flows is thought to be governed by velocity structure, variation in structure would suggest mass may be transported differently in each condition. Overall, we suggest that ash transport and plume motion for Strombolian eruptions may be sensitive to their time-varying discharge conditions. Thus the practice of interpreting Strombolian plume heights as a measure of either the total amount of erupted material or the instantaneous discharge rate may not be sufficient. Instead, a record of Strombolian plume rise over time may provide information about the evolution, rather than the magnitude, of the discharge over time.