Abstract
TITAN2D, VolcFlow, LAHARZ, and ∆H/L or energy cone models each employ different rheologies or empirical relationships and therefore differ in appropriateness of application for different types of mass flows and topographic environments. Previous work has focused on single-deposit comparisons of models. In this work, these models are used to recreate the inundation areas of the dense-basal undercurrent of all 13 mapped, land-confined, Soufriere Hills Volcano dome-collapse pyroclastic density currents (PDCs) emplaced from 1996-2010 to test the relative effectiveness of different computational models. Best-fit model results and their input parameters are compared with results using observation- and deposit-derived input parameters and those using empirically-derived input parameters from the FlowDat global database (Ogburn, 2012, 2014; Ogburn et al. 2016). Not only does this work provide a useful comparison of the operational aspects and behavior of various models, but it also enriches conceptual understanding of the dynamics of the PDCs themselves. Results indicate that TITAN2D is able to reproduce inundated areas well using flux sources, although velocities are often unrealistically high. VolcFlow is also able to replicate flow runout well, but does not capture the lateral spreading in distal regions of larger-volume flows. Both models are better at reproducing the inundated area of single-pulse, valley-confined, smaller-volume flows than sustained, highly unsteady, larger-volume flows, which are often partially unchannelized. LAHARZ is fast to run and can give a rough approximation of inundation, but there are problems with deriving the equation coefficients for PDCs and the designation of starting locations. The ∆H/L cone model is also very quick to run and gives reasonable approximations of runout distance, but does not inherently model flow channelization or directionality and thus unrealistically covers all interfluves.
Highlights
Pyroclastic Density CurrentsHigh concentration pyroclastic density currents (PDCs) are hot avalanches of volcanic rock and gas which, due to their ability to travel great distances at high speeds, are among the most destructive volcanic hazards
To produce best-fit model runs, basal friction is varied in TITAN2D, constant retarding stress (CRS) is varied in VolcFlow, and the coefficients C and c and starting locations are varied for LAHARZ
Best-fit results are compared with “non-calibrated” deposit-derived results obtained using only observed PDC data as input parameters; namely, deposit-derived basal friction (∆H/L), deposit-derived CRS, globally-derived LAHARZ coefficients, and the global ∆H/L vs. volume regression. This allows a comparison of TITAN2D, VolcFlow, LAHARZ, and ∆H/L cones from both a fully calibrated or “best-fit” perspective, and from the perspective of a modeler using only past deposits to estimate model inputs
Summary
High concentration pyroclastic density currents (PDCs) are hot avalanches of volcanic rock and gas which, due to their ability to travel great distances at high speeds, are among the most destructive volcanic hazards. The transport of these flows has been a topic of much debate and research (e.g., Sparks, 1976; Francis and Baker, 1977; Dade and Huppert, 1998; Burgisser and Bergantz, 2002, etc.). The complexity and limited understanding of many aspects of the physics of PDCs make predicting the behavior of these flows using empirical or physical models challenging, as every model must make simplifications. Determining which of these simplified models are useful for simulating different volume PDCs, in different environments, and with different operational constraints remains a problem
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