The changing morphology of an open lava channel on Mt. Etna

Abstract

An open channel lava flow on Mt. Etna (Sicily) was observed during May [30][31] 2001. Data collected using a forward looking infrared (FLIR) thermal camera and a Minolta-Land Cyclops 300 thermal infrared thermometer 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 peaking 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 generally overspill the channel to emplace pāhoehoe overflows.Editorial responsibility: A. Woods 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'ā 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 pāhoehoe sheets during pulses, and as slow-moving 'a'ā units during backup. Small, localized fluctuations in channel volume flux also occurred on timescales of minutes. Volumes of lava backed up behind 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, downchannel surges. Real fluctuations in channel volume flux, due to pulses and surges, can lead to significant errors in effusion rate calculations.

Morphology and structure of the 1999 lava flows at Mount Cameroon Volcano (West Africa) and their bearing on the emplacement dynamics of volume-limited flows

“…Also, the pahoehoe drapes for the 1999 lavas extend no more than 15 m from the channel and are usually < 1 m thick. This ties with observations at Etna (Bailey et al 2006) and underlies the unsteady nature of flow within the channel.…”

“…In laminar flow the central region of the channel moves faster than the flow margins where shear is highest. Thus lava surfaces in the centre have experienced less cooling and less shearing than lava surfaces at the channel margins (Flynn & MouginisMark, 1994;Bailey et al 2006). As a consequence, the flow centre can remain as pahoehoe, whereas the cooler and more sheared margins develop an aa clinker texture as illustrated in Figure 3a.…”

“…Overflow levees are generally formed following a flow surge or pulse, or a gradual rise in the lava level as a function of down-slope cooling (Sparks, Pinkerton & Hulme, 1976;Bailey et al 2006). They are generally thin and have limited extent, indicating they were supplied by pulses of short-lived liquid lava (Harris et al 2009).…”

“…Detailed studies of basaltic or basaltic andesite lava flows have been dominated by investigations at only a few volcanoes, for example, Hawaiian volcanoes (Soule, Cashman & Kauahikaua, 2004;Harris et al 2009;Ball, Pinkerton & Harris, 2008), Longquimay, Chile (Naranjo et al 1992) and Etna, Italy (Polacci & Papale, 1997Calavari & Pinkerton, 1998Guest et al 1987;Guest & Stofan, 2005;Bailey et al 2006). There is need to examine case studies elsewhere.…”

Early Analysis of Landsat-8 Thermal Infrared Sensor Imagery of Volcanic Activity

“…Given such data, previous workers have often gone on to calculate lava effusion rates. This is not done here as the data are based on just one observation and [41] shows that variations in lava effusion rates may occur over timescales of tens of minutes, suggesting that such instantaneous readings might not be truly representative. However, the instantaneous value does provide a useful indicator against which the volcano's activity can be compared with similar data recorded at other volcanoes.…”