Hancock, Anson and James, Michael and Blackburn, George (2018) Understanding emplacement of rapidly-emplaced volume-limited lava flows from Mount Etna’s 2011-2012 eruption : a multidisciplinary study. PhD thesis, Lancaster University.
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Abstract
While the study of emplacement in most literature focuses on long-duration cooling-limited lava flows, the short duration and rapid emplacement of many volume-limited flows impedes their analysis. This thesis aims to improve understanding of the emplacement of shortduration volume-limited lava flows by: (1) employing long-range ground-based visible timelapse data and thermo-rheological modelling to understand and analyze the importance of different factors which influence lava flow emplacement, and (2) developing a workflow for improving the application of long-range ground-based thermal cameras for studying lava flows. Results from (1) agreed with previous studies, showing strong correlations between final flow length and the following: total volume, duration, flow field width, number of bifurcations in the proximal zone of the flow, number of confluences, average and maximum advance rate in the proximal zone, and duration of fire fountaining. However, unlike previous studies, no correlation was found between final flow length and mean output rate. Visual analysis identified two flow groups based on morphology within the proximal zone of the flow, and results indicated that differences in advance rates and at-vent initial effusion rates dictated the morphology observed for the two groups. Analysing flow confinement indicated a strong relationship between final length and the distance of confinement of the primary flow. Utilising multiple regression analysis, maximum flow width, duration of flow, and maximum advance rate in the proximal zone produced the best model for flow length in terms of explanatory and predictive power. By substituting flow widths estimated from the time-lapse data for channel widths, FLOWGOmodelled effusion rates and total volumes were obtained for the primary flows of the 12 May and 19 July 2011 episodes at Mt. Etna which were within the range of values estimated by previous studies. Additionally, using FLOWGO to model flow thickness changes due to bifurcations of the primary flow produced average flow thickness estimates for the semichannelized 12 May flow that agreed with estimates from previous studies. However, no thickness estimates were possible using this method for the unconfined 19 July flow. This suggests that substituting flow width for channel width in FLOWGO for unconfined flows is inappropriate and should only be applied to flows with a more channel-like morphology. A workflow was developed to achieve objective (2) and applied to the 29 August 2011 episode at Mt. Etna to correct ground-based thermal data for atmospheric and viewing effects due to long viewing paths along two different viewing geometries (horizontal- and slant-path). Estimates of flow area, volume, and mean output rate using both viewing geometries were within the range of values reported in the literature. Estimates of surface temperature using the slant-path geometry were within the range of values given by previous studies which measured active lava channels at 0-70 metres distance; however, the complexity of the atmospheric model associated with this viewing geometry made it difficult to automate. Some errors resulted from the large pixel area (25 m2 ) of the long-range thermal data resulting in a greater area of temperature integration. The radiant heat flux profiles produced by the workflow followed the same trends as the SEVIRI-derived profile, although the intensity of the SEVIRI-derived profile was up to five times greater than the workflow profiles.