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Title: Palaeo-volcanological reconstructions of explosive eruptions from limited outcrops
Author: Burden, R. E.
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2013
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A key goal in volcanology is to develop long-term hazard and risk models for future volcanic events. For low frequency, large magnitude Plinian eruptions these assessments are based on the geological record of past eruptions. However, many deposits are poorly preserved and reveal very little information about the deposit. This thesis aims to develop methods for extracting additional information from these poorly preserved deposits, focussing on the estimation of erupted volume and eruption column height, and constrain uncertainties in the values found. A key development in this thesis is the quantification of a standardised field technique for characterising maximum clast-measurements, which are used to estimate plume heights. Bayesian inversion of the different techniques shows that the current recommendation for standardising maximum-clast measurements, the 50th percentile of 20 clasts, produces accurate results for reconstructing plume height. Plume height is a key parameter used to model future eruption scenarios, therefore the uncertainties associated with this parameter need to be quantified. Here a method has been developed that quantifies this uncertainty, dependent on the preservation and exposure of the deposit. An alternative statistical method to objectively determine the volume of a fall deposit without the production of isopach maps is presented. Integration of a log-linear regression model for thickness measurements with distance from the vent is applied to field measurements without any prior interpretation. Data and model uncertainty is accounted for using Bayesian methods. The eruption volumes calculated correspond well, and are within 10 %, to those previously determined by alternative methods. The number and distribution of thickness and maximum clast measurements from fall deposits can limit the amount of information gained from the deposit. Application of a fixed point variogram to field measurements identified the dependency of the deposit structure, with respect to the vent location, on spatial distribution of measurements. Results suggest that measurements need to be evenly distributed across a deposit, not concentrated along a dispersal axis. The methods developed in this thesis provide objective ways to calculate parameters from fall deposits and constrain the uncertainty in these parameters when limited data is available. This is important for modelling the long-term hazard and risk for future volcanic events.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available