Numerical Modeling of Pumice Clast Heat Transfer and Transport Dynamics in Subaqueous Eruptions

Abstract:

A multi-scale numerical model is presented to quantify erupted pumice heat transfer, subsequent water infiltration, and emplacement in the water column, at the surface or the seafloor. Quantifying mass partitioning of erupted material in different regions of the water column, syn- and post-eruption, will elucidate the mechanisms of particle transport, identify an eruption’s surface-breaching/raft-development potential, and aid in assessing the impact on local biota and marine shipping and navigation.

The relationship between heat transfer and pumice transport in the presence of water is an important and non-trivial topic to the volcanological community. It has been shown experimentally that cold pumice remains afloat for days to months, whereas heated pumice will sink in seconds (Dufek et al. 2007; Allen et al., 2008). Yet, in nature, it is observed that pumice can be erupted and travel to the surface to form extensive pumice rafts (Gass et al., 1963; Jutzeler et al., 2014). This phenomenon can result from insufficient heat removal during transport, clast cooling before substantial contact with water, or by a deviation from typical subaerial clast texture due to the presence of water. The answer to this anomalous behavior will be found through a combination of experimentation, numerical modeling, and textural classification.

We present a multi-scale numerical model to predict the physical contributions of water to the texture development and transport of an erupted pumice clast. This calculation adapts an Eulerian-Eulerian-Lagrangian (EEL) approach for submarine environments and includes clast scale heat transfer, disequilibrium bubble growth, hydrous phase change, and advection through porous media (Syamlal, 1987; Dufek and Bergantz, 2007; Benage et al., 2014). The heat transfer model has been verified against an analytical model for spherical conduction and external convection and compared to pumice-scale experiments. The model has been evaluated over a range of clast sizes, vesicularities and vesicle distributions, and eruption conditions to identify the dispersal regimes of pumice.

The model is readily adaptable to measurements of products from the 2012 eruption of the Havre seamount and other eruptions, and will use this information as further analysis on these eruptive products proceeds.