The "natural boundaries" of Etna are the rivers Alcantara and Simeto on the North, West, and South, and the sea on the East to the extent of 23 miles of coast, along which lava streams have been traced, sometimes forming headlands several hundred feet in height. The base of the mountain, as defined by these natural boundaries, is said to have a circumference of "at least 120 miles," an examination of the new map, however, proves that this is over-estimated.
If we take the sea as the eastern boundary, the river Alcantara, (immediately beyond which Monte di Mojo, the most northerly minor cone of Etna is situated), as the northern boundary, and the river Simeto as the boundary on the west and south, we obtain a circumference of 91 miles for the base of Etna. In this estimate the small sinuosities of the river have been neglected, and the southern circuit has been completed by drawing a line from near Paterno to Catania, because the Simeto runs for the last few miles of its course through the plain of Catania, quite beyond the most southerly stream of lava. The Simeto (anciently Simæthus) is called the Giaretta along the last three miles of its course, after its junction with the Gurna Longa.
The area of the region enclosed by these boundaries is approximately 480 square miles. Reclus gives the area of the mountain as 1,200 square kilometres—461 square miles. (Nouvelle Geographie Universelle, 1875.) The last edition of a standard Gazetteer states it as "849 square miles;" but this estimate is altogether absurd. This would require a circle having a radius of between sixteen and seventeen miles. If a circle be drawn with a radius of sixteen miles from the crater, it will pass out to sea to a distance of 4½ miles on the East, while on the West and North it will pass through limestone and sandstone formations far beyond the Alcantara and the Simeto, and beyond the limit of the lava streams.
There are two cities, Catania and Aci Reale, and sixty-two towns or villages on Mount Etna. It is far more thickly populated than any other part of Sicily or Italy, for while the population of the former is 228 per square mile, and of the latter 233, the population of the habitable zone of Etna amounts to 1,424 per square mile. More than 300,000 persons live on the slopes of the mountain. Thus with an area rather larger than that of Bedfordshire (462 square miles) the mountain has more than double the population; and with an area equal to about one-third that of Wiltshire, the population of the mountain is greater by nearly 50,000 inhabitants. We have stated above that the area of Etna is 480 square miles, but it must be borne in mind that the habitable zone only commences at a distance of about 9¼ miles from the crater. A circle, having a radius of 9¼ miles, encloses an area of 269 square miles; and 480 minus 269 leaves 211 square miles as the approximate area of the habitable zone. Only a few insignificant villages on the East side are nearer to the crater than 9¼ miles. Taking the inhabitants as 300,000, we find, by dividing this number by 211, (the area of the habitable zone), that the population amounts to 1,424 per square mile. Even Lancashire, the most populous county in Great Britain, (of course excepting Middlesex), and the possessor of two cities, which alone furnish more than a million inhabitants, has a population of only 1,479 to the square mile.
Some idea of the closeness of the towns and villages may be found by examining the south-east corner of the map. If we draw a line from Aci Reale to Nicolosi, and from Nicolosi to Catania, we enclose a nearly equilateral triangle, having the coast line between Aci Reale and Catania as its third side.
Starting from Aci Reale with 24,151 inhabitants, and moving westwards to Nicolosi, we come in succession to Aci S. Lucia, Aci Catena, Aci S. Antonio, Via Grande, Tre Castagni, Pedara, Nicolosi, completing the first side of the triangle; then turning to the south-east and following the Catania road, we pass Torre di Grifo, Mascalucia, Gravina, and reach Catania with 85,055 inhabitants; while on the line of coast between Catania and Aci Reale we have Ognina, Aci Castello, and Trezza. Within the triangle we find Aci Patane, Aci S. Filippo, Valverde, Bonacorsi, S. Gregorio, Tremestieri, Piano, S. Agata, Trappeto, and S. Giovanni la Punta: in all twenty-five, two of which are cities, several of the others towns of about 3,000 inhabitants, and the rest villages. These are all included within an area of less than thirty square miles, which constitutes the most populous portion of the habitable zone of Etna.
That the population is rapidly increasing is well shown by a comparison of the number of inhabitants of some of the more important towns in 1824 and in 1876.[15]
Catania Aci Reale Giarre Paternò Aderno Bronte Biancavilla Linguaglossa Randazzo Piedimonte Etnea Zaffarana Etnea Pedara Trecastagni | 1824 45,081 14,094 13,705 9,808 6,623 9,153 5,870 2,415 4,700 1,404 700 2,068 2,406 | 1876 85,055 24,151 17,965 16,512 15,657 15,081 13,261 9,120 8,378 4,924 3,884 3,181 3,061 |
The general aspect of Etna is that of a pretty regular cone, covered with vegetation, except near the summit. The regularity is broken on the East side by a slightly oval valley, four or five miles in diameter, called the Val del Bove, or in the language of the district Val del Bue. This commences about two miles from the summit, and is bounded on three sides by nearly vertical precipices from 3,000 to 4,000 feet in height. The bottom of the valley is covered with lavas of various date, and several minor craters have from time to time been upraised from it. Many eruptions have commenced in the immediate neighbourhood of the Val del Bove, and Lyell believes that there formerly existed a centre of permanent eruption in the valley. The Val del Bove is altogether sterile; but the mountain at the same level is, on other sides, clothed with trees. The vast mass of the mountain is realised by the fact that, after twelve miles of the ascent from Catania, the summit looks as far off as it did at starting. Moreover, Mount Vesuvius might be almost hidden away in the Val del Bove.
A remarkable feature of Etna is the large number of minor craters which are scattered over its sides. They look small in comparison with the great mass of the mountain, but in reality some of them are of large dimensions. Monte Minardo, near Bronte, the largest of these minor cones, is still 750 feet high, although its base has been raised by modern lava-streams which have flowed around it. There are 80 of the more conspicuous of these minor cones, but Von Waltershausen has mapped no less than 200 within a ten mile radius from the great crater, while neglecting many monticules of ashes. As to the statement made by Reclus to the effect that there are 700 minor cones, and by Jukes, that the number is 600, it is to be supposed that they include not only the most insignificant monticules and heaps of cinders, but also the bocche and boccarelle from which at any time lava or fire has issued. If these be included, no doubt these numbers are not exaggerations.