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Volcanoes: eruptive style, pre-eruptive evolution and risk

Periodic Reporting for period 1 - VESPER (Volcanoes: eruptive style, pre-eruptive evolution and risk)

Okres sprawozdawczy: 2018-02-19 do 2020-02-18

‘The biggest eruptions tend to occur at volcanoes we know nothing about’ (1).

The project studies when, why and how volcanoes erupt. We analyse volcanic deposits to understand pre-eruptive processes in deep magma reservoirs of active volcanoes in intra-plate- and subduction-related settings. The focus is on detailed description of whole-rock and mineral compositions. Our main interest is the mineral zircon that records information about magma source compositions, reservoir processes and crystallisation timescales. Zircon is chemically and physically resistant so can be recycled and register multiple events in the history of a volcano. The main objective is to understand periodicity and style of volcanic eruptions to mitigate hazards and risks to communities living near volcanoes - the past is the key to the future.

Some 800 million people live within 100 km of an active volcano (2). Thus, the necessity to study, monitor and predict volcanic hazards becomes clear, particularly when we consider that risks to people living near volcanoes may arise from both immediate local- to regional-scale impacts and longer-term hemispheric- to global-scale effects. Understanding what determines whether a volcanic eruption is explosive or effusive is a key factor in hazard and risk assessment and mitigation planning.

The overall objective of the project is to obtain information about magma storage conditions and plumbing systems in relation to effusive and explosive volcanic activity. Such information may be used to consider future volcanic behaviour and so short-term, within eruption, and longer-term, between eruption, potential risks.

More specifically the project has three main objectives:

i. To combine pre-existing hazard map and volcano-stratigraphic data that summarise the extent and style of deposits of known individual volcanic events with compositions of eruptive products. Knowing volcanoes past behaviour, and so how they may behave in the future, can be applied to hazard forecasting.

ii. To track changes in magma composition recorded in whole-rocks and minerals to determine magma sources (mantle and crustal); identify possible proxies for pre-eruptive processes (melting, crystallisation, mixing and degassing); and, relate these to effusive or explosive eruptive volcanic deposits.

iii. To determine the age of characterised volcanic samples, using U-series dating, and track zircons compositional changes in inherited, assimilated and magmatic crystals.

1. Oppenheimer 2011. Eruptions that shook the world
2. Loughlin et al., 2015. Global Volcanic Hazards and Risks
Work package 1 Project Management
Project management involved all aspects of the fellowship, including the financial component. Support was given by the supervisor and host institute administrative staff. A real strength of the project is the collaborations established by the researcher - these active partnerships will last long beyond the life of the current project.

Work package 2 Training and Career Development
In addition to training-through-research whilst conducting fieldwork and geological analyses the researcher had the opportunity to attend numerous staff development courses at the host institute.

Work package 3 Outreach and Communication
The project supervisor’s active and innovative approach to outreach ( gave the researcher the opportunity to find out about new ways of engaging with the public to communicate scientific ideas. This included maintaining an active Twitter account (@huetor_vega). Working with an educationalist an outreach pack was prepared for primary school children. Other activities included participation in European Researchers’ Night events and the Norwich Science Festival.

Work package 4 Scientific, logistical and collaborative aspects of volcanological fieldwork
Fieldwork and sample collection for current and future work was undertaken on: St Vincent, Montserrat, and Ascension Island. A volcanological fieldwork planning guide was produced and refined after field training with experienced volcanologists.

Work package 5 - 1st objective - Description of eruptive style and composition of volcanic deposits
During fieldwork the researcher worked with experienced volcanologists to: describe the eruptive style and composition of volcanic deposits cropping out in the field areas: and link the extent and style of deposits of known individual volcanic events with their compositions.

Work package 6 - 2nd objective - Modelling of effusive and explosive volcanic activity
Following training in the use of modelling software, a volcanic processes model was developed and integrated with field data. The main conclusions track changes in magma compositions recorded in whole-rock and mineral compositions to determine mantle and crustal magma sources; and identify possible proxies for pre-eruptive processes, e.g. melting, crystallisation, mixing and magma volatile content.

Work package 7 - 3rd objective - Zircon geochronology
Sample preparation and analysis comprised a significant part of the project. Zircon was separated from numerous samples, an extensive collection of images and geochronological and compositional analyses were produced.

Project results have been presented at four international conferences and ten outreach events.
Zircon as a tracer of plumbing processes in an active magmatic system: insights from mixed magmas of the 2010 dome collapse, Montserrat, Caribbean
Despite being one of the world’s most studied volcanoes, to date zircon has not been characterised in the Montserrat rocks. Project results are the first zircon data from an active arc system to confirm the validity of the island-arc field in the U/Yb vs Hf tectonomagmatic discrimination diagram. Furthermore, new EHft zircon data are the first to verify the continental crust Hf isotope evolution line recently defined using modern island arc whole-rock data. Temporal constraints are placed on the physical and compositional state of the magmatic plumbing system - over tens of thousands of years - and insights are gained into pre-eruptive processes - over the last decade.

Zircon perspectives on the volcanic-plutonic connection from a complex silicic ocean island, Oki-Dōzen, Japan Sea
Study of plutonic and volcanic rocks from the same magmatic system provides insights into sources, storage conditions and dynamics including periodicity. New zircon ages integrated with thermal and chemical modelling place constraints on physical and compositional changes at set points within evolution of the magmatic system. This reveals significant amounts of unerupted material which has implications for the potential size of future eruptions.

Forensic geochronology of an explosive-effusive transition: Ascension Island, S Atlantic
A geochronological-geochemical-petrological study of major and trace element data, and zircon O-isotopic compositions of the only know explosive-effusive transition on Ascension Island has revealed closed-system 'cold' crystal storage. The main conclusion to date is that (U-Th)/He zircon ages suggest prolonged preservation of crystals in the magmatic system at <200ºC and subsequent recycling in a younger magmatic event.

Project results can be fed into models of risk at active volcanoes in intra-plate and subduction-related settings. They are of particular relevance for medium-long term hazard mitigation planning strategies.
Presentation of the project at Science is Wonderful! 2019, Brussels