Time-dependent changes in magma transfer controls and eruption triggers at a destructive volcano

Last year, positions of points on Mt Etna volcano showed a sudden change in their sense of movement. Instead of moving outward and downward as they had done for the previous 10 years, they contracted inwards. This suggested that the summit subsidence and outward spreading of the volcano under its own weight, which was considered the major factor in determining where and when eruptions occurred, had stopped, and that therefore it was likely that the recent series of eruptions would also stop. Last weekend, a new fissure opened down the eastern side of Mt Etna, with strombolian explosions and lava now being emitted at a high rate, a quite unexpected event which contradicts both principal hypotheses that have been advanced to explain the structural control of eruptions: magma pressure and gravitational spreading. Most interestingly, it raises the possibility that these controls might be time-dependent phenomena, alternating with regional tectonic movements as the dominant influence on the internal workings of the volcano and the triggering of eruptions. However, before we can conclude anything, we need to measure the points that we measured last year as soon as possible, to try and detect whether the observed movement 2004-2005 is a temporary blip (perhaps associated with the unusual 2004-5 eruption) upon a general trend, or whether it represents a radical new departure indicating a change in behaviour of the volcano. We can only do this if we measure it in the next few weeks, preferably before the eruption has stopped, and certainly before it has had time to recharge its magma storage areas and complicate the picture. To do this I will need a decision within the next week or two, in order to organise and prepare for the fieldwork in time. The results of such an investigation are far-reaching. We need to understand the functioning of a frequently-active volcano such as Etna in order to understand the 500-odd other active volcanoes that erupt too infrequently for such critically fine distinctions to be either elucidated or measured. If controls on magmatic activity and eruptive behaviour can radically change with time, as the 2004-5 measurements and this new 2006 eruption suggest, then this determines what parameters need to be measured at other less well-studied or understood volcanoes. The present eruption represents a unique opportunity to make highly critical measurements in a strictly time-limited window.