Pyroclastic density currents (PDCs) are hot, density-driven flows of gas, rock and ash generated during explosive volcanic eruptions, or from the collapse of lava domes (e.g. Sparks, 1976; Fisher, 1979; Branney and Kokelaar, 2002; Cas et al. 2011) posing a catastrophic geological hazard, and causing >90 000 deaths since 1600 AD (Auker et al. 2013). Improved understanding of PDCs will enable us to better understand the explosive eruptions that generate them, improving preparedness for future volcanic events. However, these deadly hazards are rarely observed up close and are difficult to analyse in real-time. To understand the flow dynamics of density currents we must use models and interpretations of their deposits (e.g. Smith N and Kokelaar, 2013; Rowley et al. 2014, Williams et al. 2014, Sulpizio et al. 2014; Lube et al. 2019, Pollock et al 2019, Smith 2018, 2019).
Interpreting the rock record at volcanoes is the primary way in which volcanologists assess the hazards that the volcano poses to communities. However, the rock record of PDCs is incomplete – currents can pass over the landscape without depositing and they can even erode their own deposits. Sometimes the sedimentary structures within these deposits are difficult to interpret. But, deciphering the structures in that deposit enables us to understand the evolution of an eruption; was there a single, large sustained current, or a series of discrete currents, possibly prior to a climactic caldera collapse? Did multiple currents traverse different areas of the surrounding landscape, or was there a focussed zone of activity?
The number of PDCs generated during an eruption has typically been interpreted by stratigraphic evidence for a cessation in flow that defines discrete “flow-units” (e.g. Brown and Branney 2013). However, in a study where sufficient exposures were available for comparison (Smith N, 2012) it was found that different numbers of flow-units can be recorded in proximal and distal exposures, demonstrating that waxing and waning (“unsteadiness”) along a current’s run-out can create a contradictory picture of flow-units in different locations. Thus, there remains a question on the use of stratigraphic markers to define numbers of discrete PDCs.
This PhD will use field observations and laboratory experiments to explore how changes in PDC dynamics are recorded in volcanic stratigraphy, and how this information can be used to better reconstruct eruptive activity. The work will focus on how variations in current steadiness, mass flux, particle size and substrate can impact current run-out and the deposition of flow-units.
Impact:
The project will improve interpretation of the geological record of explosive volcanic events and shed light on (i) how changes in eruption mass flux and steadiness impact the run-out distance of pyroclastic density currents through time (ii) how current run-out impacts the stratigraphic record with distance from the vent and with location around the vent. This insight will improve our ability to create hazard assessments of PDC-forming eruptions. By creating better hazard maps, we can help build the resilience of local communities at risk. The work is relevant to the fields of volcanology and hazard planning, and potentially farther afield, to studies of other types of gravity currents (e.g. submarine turbidity currents and avalanches).
See the Panorama website (https://panorama-dtp.ac.uk/research/assessing-the-rock-record-of-hazardous-pulsatory-pyroclastic-density-currents/) for more information on the Project, the Supervisory Team, training and the working environment.
For more information on this research proposal, please watch this excerpt taken from a recent webinar on Panorama DTP projects: https://youtu.be/5pgbM8fxUTA
Student Profile
You should have an interest in igneous geology, volcanology, sedimentology, and geological hazards, and be enthusiastic about using a range of different techniques to better understand density current dynamics. You should have a strong background in one of the relevant degree courses (https://panorama-dtp.ac.uk/research/assessing-the-rock-record-of-hazardous-pulsatory-pyroclastic-density-currents/) (ie you should normally have, or expect to obtain, at least a 2:1 Honours degree (or international equivalent (https://www.hull.ac.uk/choose-hull/study-at-hull/international/country-search.aspx))).
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