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The effects of degassing and effusion rate fluctuations on the evolution of basaltic lava flow

Project: Funded ProjectResearch

1/01/0931/12/12

Basaltic lava flows cause significant damage to property and infrastructure on many volcanoes. To improve our understanding of the evolution of lava flows and flow fields, there is a need for an integrated multi-disciplinary study of the
physicochemical properties of lava as it moves from the vent to the flow front, and of the complex interactions that take place during flow. Key requirements are: (i) robust methods of predicting how lava rheology changes during flow; and (ii) an improved understanding of how both long- and short-term changes in effusion rates affect the complex range of processes operating during flow emplacement. This project will provide a range of measurements using new field
equipment, automated imaging procedures, ground-, helicopter- and satellite-based imagery and innovative laboratory measurements. The combined dataset will be used to develop and constrain the next-generation of lava flow models which will drive future hazard assessment and mitigation strategies on basaltic volcanoes. We propose to focus our research on one or more eruptions of Mount Etna. This collaborative and multi-disciplinary project will be undertaken jointly by the PI and Co-PIs at Lancaster, staff at INGV, Catania, and other colleagues from the USA and the UK.

Current flow models assume that rheological changes are driven mainly by surface cooling. However, rheological changes over the entire flow thickness can result from crystallisation due to degassing-related undercooling. To assess the importance of undercooling, we will determine patterns of volatile loss and rates of crystal and bubble nucleation and growth during the emplacement of active lava flows, and make accurate measurements of the rheological properties of lava in different parts of an active lava flow using a new field viscometer. Quenched samples of all lavas measured will be collected and used to determine the crystallinity, vesicularity and composition of residual glass of all samples in collaboration with colleagues at INGV, Catania, and the University of Oregon. Vesicle size distributions, porosity and an assessment of bubble coalescence and connectivity (and hence the potential for gas loss during flow) will be made at Lancaster using a state-of-the-art X-ray tomographic scanner. Measurements of volatile loss during emplacement will be undertaken in a new Magma Volatile Laboratory at Lancaster using a coupled Thermogravimetric Analysis - Differential Scanning Calorimeter - Mass Spectrometer, and these will allow the potential effects of undercooling to be quantified and compared with changes in crystal size distribution. These combined laboratory and field measurements will allow us to reconstruct the entire volatile degassing budget of a lava flow for the first time, and to assess the importance of degassing in controlling the emplacement of lava flows.

The above measurements will be used in combination with a comprehensive time-series of thermal images and digital terrain models of an evolving lava flow field to understand and quantify the processes responsible for flow field evolution. Digital terrain models will be created using long range laser scanner data, augmented by oblique photogrammetric data from ground-based imagery from a new network of high-resolution cameras. These will be supplemented by helicopter imagery collected by INGV, Catania, and Hyperion satellite data in collaboration with a colleague at the Jet Propulsion Laboratory. The data acquired using the combined rheological/degassing and imaging measurements will, for the first time, enable the emplacement processes/flow behaviour to be directly linked to the cooling, degassing and crystallisation of the lava in both simple and more complex flow fields. While the work will be undertaken on lavas from Mount Etna, the methodologies developed in this project have major applications for many other volcanoes and are in line with NERC's strategic and scientific priorities 2007-2012.