Approaches in Experimental Volcanology: Bench-Scale, Field-Scale and Mathematical Modelling of Maar-Diatreme Systems

Andrews, Robin George

In recent decades, major fieldwork studies have greatly advanced our knowledge of maar-diatreme systems, the second most common type of volcano; despite this, much of the interpretation is strongly debated. My original contribution to volcanological research is twofold: firstly, successfully simulating maar-diatreme systems using analogue experimentation in order to determine the processes that generate them; secondly, using mathematical modelling to produce a predictive model for their total energy release during an eruption. This study uses a tripartite, quantitative approach: (1) bench-scale experiments are used to generate simulated maar-diatreme volcanoes and examine their eruption and depositional processes; (2) these are qualitatively compared and quantitatively scaled to both field-scale experiments and natural maar-diatreme volcanoes; and (3) the 1886 maar-forming Rotomahana eruption is used as a case study for a new thermodynamic model which gives a first-order calculation of the cumulative energy change during the event. This study finds that maar-diatreme volcanoes can form through both ascending and descending blast series; multiple types of diatreme can form depending on the blast pattern. Debris jets responsible for the genesis of such systems are two-tier processes: the crater excavation and upward entrainment processes are temporally segregated. The behaviour of the explosively generated cavities, the preservation potential of the system architecture, and the stratigraphic partitioning of blast energy are controlled by mathematical relationships between blast depth and energy. Comparing the simulated volcanoes’ sedimentological architecture to natural examples reveals additional information regarding their eruption history and depositional processes. Data produced by the thermodynamic modelling of the 1886 Rotomahana event corroborates with both fieldwork studies and direct observations, and reveals the eruption was overwhelmingly dominated by a thermal component; this predictive model is hypothetically applicable to similar volcanic systems. A new conceptual model of maar-diatreme formation is conceived based on a synthesis of the findings of this thesis.

321 pages A4

2015Andrews

Open Access