While the early development of basaltic lava flows is relatively well understood, long-lived effusive activity (>~3 weeks) results in complex flow field architectures with multiple ephemeral vents feeding short-lived flows, that may become tubed. The processes controlling flow structures and lifetimes are not fully understood; some may be governed by effusion rate or topography, others by rheological changes at the flow front. Detailed analyses of flow field development will improve our understanding of the above processes, and others including accidental breach formation.
During the final month of the 13 May 2008 - 6 July 2009 eruption of Mt Etna, we installed four Canon EOS 450D cameras (3 visible and one modified to collect infrared images) at critical locations to record images (at 5 or 15 minute intervals) of the active flows.
The image sequences show that multiple individual 'a'ā channel flows were often simultaneously active for hours to days, with lengths of tens to hundreds of metres. Mean flow lengths decreased over time, indicating diminishing effusion rates. Variations in the number and lengths of active flows, and the occurrence of pulses within channels are suggestive of shorter-term effusion rate fluctuations. Several flows roofed over on timescales of hours to a few days. Measured flow velocities and dimensions can be used to estimate rheological properties. Processes observed in these small flows have also been observed in larger flows, so we discuss implications for interpreting flow behaviour on larger spatial scales.