Mount Etna, Sicily: Landscape evolution and hazard responses in the pre-industrial era

Abstract

Mount Etna dominates eastern Sicily, being over 3000 m in height and covering an area of some 1750 km2. Etna has instilled a sense of awe in men and women for thousands of years (Fig. 15.1); to voyagers in the Classical Age it was considered the highest point on Earth (King 1973a) and, even before the colonization of the island by the Greeks ca. 740 BC, members of Sicel culture were practicing cults that associated volcanism with subterranean processes (Chester et al. 2000). Volcanologically Etna is not only large, but also one of the few continental volcanoes that is continually active. Etna's volcanic activity was initiated about 300-400 ka BP in what was then a marine gulf on the east coast of Sicily (Bonaccorso et al. 2004). Etna's last catastrophic eruption occurred around 15,000 years ago, led to caldera collapse and the eruption of hot and potentially highly destructive pyroclastic flows, which swept down the southwestern flank of the volcano (Guest et al. 2003). Since then Etna has been characterized by basaltic activity, with the principal hazard being posed by lava flows. The vast majority of lava flows on Etna show aa morphology with a rough surface made up of irregular lava fragments. The name 'aa' is derived from the onomatopoeic Hawaiian word a'a, which means hard to walk on, but a small proportion of flows show 'pahoehoe' morphology, again an Hawaiian word and typically describing a flow with smooth, lobate and undulating surfaces. There have been very infrequent explosive eruptions, which are unusual on a basaltic volcano, and these have deposited a few centimeters of tephra (volcanic ash) beyond the margin of the volcano. One example of such an event was the eruption of 122 BC when tephra fall brought about extensive damage to Catania during the Roman era and, more recently, tephra from the 2001 eruption caused considerable disruption to communications. In terms of the relationships between people, land, and the creation of distinctive landscapes, Etna is fascinating because, in spite of the ever present threat of volcanic eruptions and earthquakes, since ancient times the region has attracted settlers in large numbers. Catania, the principal city of the Sicilian east coast, has been badly affected by both these phenomena, and during the past 2000 years has been destroyed in part by earthquakes in 1169 and 1693, and by lava flows in 1669 and probably also in 1371 or 1381, the dating being uncertain (Chester et al. 1985, 2005). This paradox between the hazardous character of the environment and the region's attractiveness for settlement may be accounted for by a number of physical and human factors which operate at two distinct scales. Etna occupies an east coast location within Sicily (Fig. 15.1) and at an all-island scale part of the reason for its development is related to deep-seated and longrecognized contrasts between the coastlands and the interior, which Italian geographers commonly refer to as the "ugly picture in a frame of gold: the dry poverty- stricken core of the island contrasting vividly with the intensively-cultivated, irrigated coastal periphery" (Fig. 15.2; Milone 1960; King 1973a, p. 112). At the more detailed scale Etna has developed in a distinctive way, not just because people have had to respond to hazards, but also through a combination of factors that include not only particularities and variations in climate, vegetation and soils, but also distinctions caused by history, economy and culture. This makes the Etna region in some respects similar to, yet distinct from, other portions of the "frame of gold" (King 1973a, p. 112) and its unique character has made it of interest not just to volcanologists and other earth scientists, but also to classicists, historians and prehistorians, geographers and rural-sociologists (Leighton 1996, 1999; Chester et al. 2000; Malone and Stoddart 2000; Duncan et al. 2005; Smolenaars 2005). Although important social and cultural particularities remain, today Sicily is closely integrated into the economies of Italy and the wider European Union, but even as late as the late 1960s and early 1970s major elements of the pre-industrial society still persisted and reflected an interplay of people and environment that had produced distinctive agricultural landscapes and which had developed over hundreds, in some cases thousands, of years of settlement. For instance, the 1971 census recorded a Sicilian population of around 5 million, of which the percentage employed in agriculture varied from 20% to 40% depending on province, with an estimated 50% of the island population still dependent on agriculture to some degree (King 1971). Administratively most of the land area of Etna is contained within the Province of Catania and, reflecting its "frame of gold" location and other more localized features of attraction, accounted for 20% of the population of Sicily and some of the highest popu lation densities found on the island. In 1971 figures of up to 800 persons/km2 occurred in local authority areas ('comuni') located close to Catania, whilst elsewhere densities of 500 persons/km2 were far from uncommon, densities declining with both increasing height on the volcano and with increasing distance from Catania. In contrast, for the island as a whole, an average population density in 1971 was 181 persons/km2. © Springer Science+Business Media B.V. 2010.