Abstract
Accurate forecasts of lava flow length rely on estimates of eruption and magma properties and, potentially more challengingly, an understanding of the relative influence of characteristics such as the apparent viscosity, the yield strength of the flow core, or the strength of the surface crust. Consequently, even the most straightforward models of lava advance involve sufficient parameters that constraints can be relatively easily fitted within the uncertainties involved, at the expense of gaining insight. Here, for the first time, we incorporate morphological observations from during and after flow field evolution to improve model constraints and reduce uncertainties. After demonstrating the approach on a basaltic lava flow (Mt. Etna, 2001), we apply it to the 2011-12 Cordon Caulle rhyolite flow, where unprecedented observations and syn-emplacement satellite imagery of an advancing silica-rich lava flow have indicated an important crustal influence on flow emplacement. Our results show that an initial phase of viscosity-controlled advance at Cordon Caulle was followed by later crustal control, accompanied by formation of flow surface folds and large-scale crustal fractures. Where the lava was unconstrained by topography, the cooled crust ultimately halted advance of the main flow and led to the formation of breakouts from the flow front and margins, influencing the footprint of the lava, its advance rate, and the duration of flow advance. Highly similar behaviour occurred in the 2001 Etna basaltic lava flow. The processes controlling the advance of crystal-poor rhyolite and basaltic lava flow therefore appear similar, indicating common controlling mechanisms that transcend profound rheological and compositional differences.
Highlights
Lava flows present a significant hazard in the immediate vicinity of volcanic complexes and can, in some cases, present a hazard to more distal communities
A Cooling Limited Rhyolite Lava Flow rate and extent of lava flow advance, which is essential for adequate hazard forecasting over a broad range of lava geochemistries, remains elusive due to the complexity of lava flow rheology, internal architecture, and interactions with topography
We use observations of the 2011–2012 Cordón Caulle rhyolite lava flow as an unparalleled opportunity to study a high-silica flow, and we present the first modeling study to our knowledge that examines the advance of a high viscosity and crystal-poor lava
Summary
Lava flows present a significant hazard in the immediate vicinity of volcanic complexes and can, in some cases, present a hazard to more distal communities. The optimized fixed parameter model provides a best fit to observed flow lengthening for a viscosity of 3.3 × 109 Pa s, a crustal yield strength of 2.5 × 108 Pa and a transition from viscosity to crustal control after 60 days (Figure 10A) This lower viscosity, an order of magnitude less than estimates for later lava (Farquharson et al, 2015), could be representative of initially. Reducing the crustal yield strength by an order of magnitude to 107 Pa in the fixed parameter approach (Equations 1, 2) produces a significant increase in modeled lava flow advance rate in the crustal control regime (Figure 11C) compared to the original model (Figure 9A), and increases the final lava flow length by >1.5 km. The effect on the flexible parameter models of lowering crust yield strength (Equations 3, 4) is not as pronounced (Figure 11D), but leads to an increase in the final flow length compared to the original model (Figure 9B), and provides a closer fit to the actual flow lengthening
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