Downloaded from http://sp.lyellcollection.org/ by guest on September 24, 2021 Mount Etna: monitoring in the past, present and future HAZEL RYMER l, FABRIZIO FERRUCCI 2 & CORINNE A. LOCKE 3 1 Department of Earth Sciences, The Open University, Walton Hall, Milton Keynes, Bucks, MK7 6AA, UK 2 Dip. di Scienze della Terra, Universita della Calabria, 87036 Arcavacata di Rende, Cosenza, ltah" 3 Department of Geology, The University of Auckland, Private Bag 92019, Auckland, New Zealand Abstract: Mount Etna is important to the economy of eastern Sicily, with agriculture and summer and winter tourism providing employment for thousands of people. Although there are no permanent homes within 10 km of the summit, year-round human activities on the upper slopes are proliferating and the risks from even a small eruption are consequently magnified. The earliest form of monitoring at Etna, as for other volcanoes, was direct observation. Modern volcano monitoring at its most effective is a synergy between basic science and hazard assessment. A prerequisite to effective monitoring is an understanding of volcanic structure and history. Sir Charles Lyell was among the first to make systematic observations of Mount Etna and laid the foundation of more modern studies. A huge array of monitoring techniques has been tested on Etna: methods that have proved successful in monitoring and sometimes in predicting eruptions include observations of seismicity, ground deformation and microgravity. These. together with electromagnetic, magnetic, gas geochemistry and various remote sensing techniques have also provided key information on the volcanic plumbing system and the eruption process. Monitoring techniques were formerly based on the most easily measured phenomena: other effects were either not recorded or were treated as noise. Future progress will be enhanced by taking account of these more subtle or complex effects and by the more comprehensive acquisition and real-time analysis of continuous data sets over extended periods. Important monitoring techniques and strategies available both now and in the near future are reviewed here in the context of Etna. The need to develop a reliable scientific platform for routine and inexpensive volcano monitoring throughout the world is highlighted. typically, with the exception of relatively infre- Why monitor volcanoes? quent large explosive events, eruptions seriously Volcano monitoring serves two key functions: it affect only a few square kilometres at most. As provides basic scientific data to develop our populations expand, however, more people are at understanding of the structure and dynamics of risk from the direct or indirect impact of volcanic volcanoes and is crucial for hazard assessment, eruptions. In addition to the immediate hazards eruption prediction and risk mitigation at times of posed by eruptive products to life, property and volcanic unrest. Monitoring provides the means to food production, volcanic activity of any kind may address questions of vital interest to communities have a significant effect on the economy. During affected by impending eruptions, such as: When minor eruptions tourism may increase and boost the and where will the volcano erupt? Which areas are local economy. The loss, however, of agricultural safe or dangerous? When will eruptions cease? farm land, farmhouses, communication and service Optimal interpretation of data from monitoring, infrastructure (roads, ports, water supplies, electric especially for the purpose of prediction, depends cables, etc.) and permanent changes in the local critically on an adequate scientific understanding of ground water and drainage system can have severe volcano structure and processes, both in general economic consequences. A volcanic disaster on one and for each specific volcano. Thus, volcano side of the world can now have a significant eco- monitoring at its most effective is a synergy nomic impact on countries on the other. Insurance between basic science and hazard assessment. companies are particularly vulnerable because of Historically, volcanic activity has been con- this, but governments are also at risk. The National sidered to be primarily of local interest because Plan for volcanic emergencies at Mount Vesuvius RYMER, H., FERRUCC1, F. & LOCKE, C. A. 1998. Mount Etna: monitoring in the past, present and future. 335 In: BLUNDELL.D. J. & SCOTT. A. C. (eds) Lvell: the Past is the Key to the Present. Geological Society. London, Special Publications. 143. 335-347. Downloaded from http://sp.lyellcollection.org/ by guest on September 24, 2021 336 H. RYMER ET AL. for example forecasts that around 700 000 people A more recent hazard posed by volcanoes is the would need to be evacuated during a period of effect of volcanic ash clouds on transportation. unrest preceding an explosive eruption such as the There have been more than 80 incidents since 1982 one that occurred in 1631. The cost of evacuation of jet aircraft encountering volcanic ash, with tens and resettlement would represent a significant of millions of dollars worth of damage done on fraction of Italy's GNP and the rest of the EU each occasion (e.g. Casadevall 1994). Millions of would certainly suffer economically from such an US dollars have also been lost to the aviation event. industry as a result of disruption when flights have Links between global climate change and been diverted or made emergency unscheduled volcanic eruptions have been postulated and there landings. Catania international airport has been is good evidence for a relationship between large closed on several occasions in the last 20 years as a explosive ash injection to the stratosphere and result of ash on the runway and the plume inter- unseasonal weather. Well documented examples secting the flight path of planes. The Messina- include the 1815 eruption of Tambora (Indonesia) Catania motorway was closed in 1995 when which was followed by the 'year without a accumulating ash made the surface slippery and summer' in the northern hemisphere, and more dangerous (J. B. Murray, pers. comm.). recently E1 Chichon (1982) and Pinatubo (1991) It is therefore of interest to all nations that (described for example in Francis 1993). In each volcanoes are monitored so that eruptions can be case there is some doubt as to the extent of climate predicted and mitigating action taken. Successful change (caused by cooling due to increased high mitigation of the local effects of an eruption (such altitude aerosols) during these short explosive as lava flow diversion and community evacuation) eruptions, but it is likely that longer-lived eruptions requires a detailed understanding of the eruption such as the 1783 lava eruption at Laki (8 months)+ process, for which monitoring data are a vital have a more prolonged effect on local and global component. More widespread effects can be miti- temperatures. gated to some degree with early warning, for Fig. 1. Location map of the eastern flank of Mount Etna showing: (I) the eruptive fissure of 14-15 December 1991; (2) northeast and south-southeast trending fractures of 1989: (3) area covered by lava flows of the 1991-1993 eruption (after Calvari et al. 1994). Downloaded from http://sp.lyellcollection.org/ by guest on September 24, 2021 MOUNT ETNA 337 example allowing aircraft re-routing. Similarly, an Buch by suggesting that Etna lavas had been appreciation of the climatic effects both locally and erupted in thin sheets on to a subhorizontal surface globally requires data from surveillance before, above sea level accumulating to a considerable during and after eruptive activity. thickness. These were thought to have then been uplifted along the line of the Valle de Bove. Historical activity and observations at Elie de Beaumont's work focused Sir Charles Etna Lyell's mind on how volcanoes formed; Lyell visited Etna on a number of occasions and in 1858 Volcanic activity in Sicily has been focused at Etna The Royal Society published a monograph titled: since the Mid-Pleistocene, resulting in the On the Structure of Lavas which have Consolidated development of one of the largest active continental on Steep Slopes: with Remarks on the Mode of volcanoes in the world (Chester et al. 1985). The Origin of Mount Etna and on the Theory of landscape of eastern Sicily is dominated by the 'Craters of Elevation ', in which he describes his edifice of the Etna volcano, which rises from sea own work and that of others and condemns the level to over 3300 m. Its activity, which com- 'craters of elevation' hypothesis (Lyell 1858). From menced some 230 000 years ago (Kieffer 1985), the morphology and flow characteristics of historic has been recorded for the last 3500 years and in and ancient lava flows he deduced that they had considerable detail for the last 400 years. Activity solidified on steep slopes. He also determined from at this basaltic volcano occurs both at the summit Valle de Bove exposures that there were two and on the flanks. Effusion rates from the summit eruptive centres, the present summit (Mongibello) are generally moderate and at least one of the and the Trifoglietto centre to the east (Fig. 1 ). Lyell several vents appears to be open to the feeder declared: system at any one time (Chester et al. 1985). As ... we must abandon the elevation-crater hypo- well as construction, there are periods of collapse at thesis; for although one cone of eruption may the summit vents resulting in ash clouds. Flank envelop and bury another cone of eruption, it is eruptions tend to be confined to specific rift zones impossible for a cone of upheaval to mantle (McGuire & Pullen 1989) and generally have a round and overwhelm another cone of upheaval higher effusion rate (Kieffer 1975) producing so as to reduce the whole mass to one conical extensive lava flows and cinder cones. Other types mountain. (Lyell 1858) of activity at this volcano include ash eruptions, pyroclastic flows and slope failure- which ranges from minor mud flows to major landslides.