Bull Volcanol (2006) 68: 497–515 DOI 10.1007/s00445-005-0025-6 RESEARCH ARTICLE John E. Bailey · Andrew J. L. Harris · Jonathan Dehn · Sonia Calvari · Scott K. Rowland The changing morphology of an open lava channel on Mt. Etna Received: 30 July 2004 / Accepted: 19 June 2005 / Published online: 7 February 2006 C  Springer-Verlag 2005 Abstract An open channel lava ﬂow on Mt. Etna (Sicily) was observed during May 30–31, 2001. Data collected us- ing a forward looking infrared (FLIR) thermal camera and a Minolta-Land Cyclops 300 thermal infrared thermome- ter showed that the bulk volume ﬂux of lava ﬂowing in the channel varied greatly over time. Cyclic changes in the channel’s volumetric ﬂow rate occurred over several hours, with cycle durations of 113–190 min, and discharges peak- ing at 0.7 m 3 s −1 and waning to 0.1 m 3 s −1 . Each cycle was characterized by a relatively short, high-volume ﬂux phase during which a pulse of lava, with a well-deﬁned ﬂow front, would propagate down-channel, followed by a period of waning ﬂow during which volume ﬂux lowered. Pulses involved lava moving at relatively high velocities (up to 0.29 m s −1 ) and were related to some change in the ﬂow conditions occurring up-channel, possibly at the vent. They implied either a change in the dense rock effusion rate at the source vent and/or cyclic-variation in the vesicle content of the lava changing its bulk volume ﬂux. Pulses would gener- ally overspill the channel to emplace p¯ ahoehoe overﬂows. Editorial responsibility: A. Woods J. E. Bailey () · A. J. Harris · S. K. Rowland Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Manoa, Honolulu, HI 96822, USA e-mail: jbailey@gi.alaska.edu Tel.: +1-808-474-6504 Fax: +1-808-474-6332 J. Dehn Alaska Volcano Observatory/University of Alaska, Fairbanks, AK 99775, USA S. Calvari Instituto Nazionale di Geoﬁsica e Vulcanologia – Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy Present address: J. E. Bailey Alaska Volcano Observatory/University of Alaska, Fairbanks, AK 99775, USA During periods of waning ﬂow, velocities fell to 0.05 m s –1 . Blockages forming during such phases caused lava to back up. Occasionally backup resulted in overﬂows of slow moving ‘a‘¯ a that would advance a few tens of meters down the levee ﬂank. Compound levees were thus a symptom of unsteady ﬂow, where overﬂow levees were emplaced as relatively fast moving p¯ ahoehoe sheets during pulses, and as slow-moving ‘a‘¯ a units during backup. Small, lo- calized ﬂuctuations in channel volume ﬂux also occurred on timescales of minutes. Volumes of lava backed up be- hind blockages that formed at constrictions in the channel. Blockage collapse and/or enhanced ﬂow under/around the blockage would then feed short-lived, wave-like, down- channel surges. Real ﬂuctuations in channel volume ﬂux, due to pulses and surges, can lead to signiﬁcant errors in effusion rate calculations. Keywords Etna . FLIR . Lava channel . ‘a‘¯ a . Thermal . Unsteady ﬂow . Morphology Introduction The ﬂow regime within channelized basaltic lava ﬂows is known to change over timescales of days, minutes and hours (Wadge 1981; Lipman and Banks 1987; Rossi 1997; Harris et al. 2000; Lautze et al. 2004). Some studies have been able to track short-term changes in lava channel morphology, volume ﬂux, cooling rates or crystallization (e.g., Lipman and Banks 1987; Crisp and Baloga 1994; Crisp et al. 1994; Cashman et al. 1999). However, interpretation and modeling of channels on timescales of <1 day has been limited by a lack of ﬁeld-based measurements of sufﬁcient temporal or spatial coverage to show critical changes (Baloga and Pieri 1986). In this regard, ﬁeld measurements are limited by the observers’ ability to continually record and accurately describe changes at ephemeral, rapidly evolving, complex, or short-lived features. Ideally, such studies would collect continuous, simultaneous measurements of temperatures