Records of and controls on temporal variations in activity at arc volcanoes

Thesis

Many attributes of volcanic activity, whether physical, geochemical/petrological, or geophysical, change over timescales from minutes to millions of years. Understanding the nature of these variations and their controls is essential both for hazard assessment and to understand volcanic and magmatic processes. Arc volcanism entails a relatively broad range of eruption styles and magma compositions, and thus wide-ranging hazards and a variety of eruption records. Despite their significance, records of activity for many arc volcanoes are inadequately characterised, so any temporal variability is poorly constrained. In this thesis, I investigate temporal variations in different styles of activity (dome-forming, Plinian-style, and effusive/glaciovolcanic) on a range of timescales (days–years, millennia, and hundreds of ky, respectively), from diverse records (seismicity, tephra deposits, and effusive eruption products), at four arc volcanoes. I analyse seismic time-series from Soufrière Hills Volcano (Montserrat) and Volcán de Colima (Mexico) using two statistical techniques, identifying temporal variation in the extent of long-range correlations and randomness in these data, which has potential to inform real-time monitoring and constrain eruptive processes. I also present new composition data for and review previous studies of tephra deposits from Volcán Hudson (Chile), revising its explosive eruption history and finding previously unrecognised shifts in the magma composition erupted through the Holocene. I also describe and analyse sequences of lithofacies from effusive eruptions of a range of magma compositions from Volcán Sollipulli (Chile), inferring varying extents of interaction with ice during their emplacement, and so changes in eruption style through time. These case studies highlight the importance of detailed characterisation of temporally varying records of volcanic activity, and some of the limitations of and uncertainties in these records and their interpretation.

Authors: Lachowycz, S

• DOI: 10.5287/ora-jvy17qav5
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: palaeoenvironment; lithofacies; entropy; eruption; Montserrat; Hudson; detrended fluctuation analysis; volcano-ice interaction; igneous geochemistry; hyaloclastite; Mexico; tephra; lava dome; Sollipulli; time-series analysis; Colima; Chile; volcano seismology; Andes; stratovolcano; Soufrière Hills; volcano monitoring; Patagonia; caldera; glaciovolcanism; palaeoclimate
• Subjects: Volcanology; Igneous rocks; Tephrochronology