HR: 14:55h
AN: V13E-06 INVITED    [Abstracts]
TI: The measurement and implications of short-term lava flux variability
AU: * James, M R
EM: m.james@lancaster.ac.uk
AF: Dept. Environmental Science, Lancaster University, Lancaster, LA1 4YQ, United Kingdom
AU: Pinkerton, H
EM: h.pinkerton@lancaster.ac.uk
AF: Dept. Environmental Science, Lancaster University, Lancaster, LA1 4YQ, United Kingdom
AU: Robson, S
EM: s.robson@ge.ucl.ac.uk
AF: Dept. Civil, Environmental and Geomatic Engineering, University College London, Gower Street, London, WC1E 6BT, United Kingdom
AB: Lava effusion rate is a critical parameter for flow models, with particular control over the potential maximum flow length attainable. However, effusion rate (or volume flux) can be extremely difficult to measure accurately in the field and is known to vary over a wide range of timescales. Here, we describe the application of computer vision and oblique photogrammetric techniques to both visible and thermal images of active aa flows in order to investigate distal flow processes at Mount Etna, Sicily, during the 2004-2005 eruption. Ground-based photogrammetric surveys were carried out (using a standard digital SLR camera) to produce repeated topographic datasets for calculation of volumetric lava flux at the flow fronts. Significant variations of the magma flux were detected (between ~0.05 and 0.35 m³s^-1), and pulses of increased flux were visible in the distal channel region on timescales of several hours. The pulses are believed to result from more frequent flux changes which were observed in the vent region. They must thus also reflect the importance of some down- flow pulse coalescence process as well as short-period variations in effusion rate at the vent. Estimates of lava effusion rate can also be made from ground-based thermal data. The effect of the observed flow variations on the thermal data is described and the implications discussed in terms of observation frequency and distance. The lava flux at the vent was estimated to be around an order of magnitude larger than that at the flow fronts, suggesting that processes such as degassing, inflation and overflows were taking place in the unobserved medial part of the flow. Consequently, when considering the advance and stopping processes for these individual flow-fronts, it must be assumed that they were fed by a highly unsteady flux, which was volumetrically significantly lower than that at the vent.
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8425 Effusive volcanism
DE: 8429 Lava rheology and morphology
DE: 8485 Remote sensing of volcanoes
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting