ETNA, an active volcano on the east coast of Sicily (Gr. Alrvn, from csfOw, burn; Lat. Aetna), the summit of which is 18 m.
N. by W. of Catania. Its height was ascertained to be Io,758 ft. in 1900, having decreased from I 0,8 7o f t. in I 861. It is the highest volcano in Europe and the highest mountain in southern Italy. Its base is elliptical (31 m. by 19 m.) and covers 46o sq.m. The Torre del Filosofo, a building of Roman date, is only 1,188 ft. from the summit. In shape it is a truncated cone, with the great rift of the Valle del Bove, a huge sterile abyss 3 m. wide, on its east side. This latter is the original crater, the volcanic axis having shifted to the present summit crater. There are some 200 subsidiary cones, some of them over 3,00o ft. high, which have risen on lateral fissures that converge toward the central crater. The mountain is built up of three superimposed parts which correspond to three distinct zones of vegetation. The lowest "regione coltivata" ex tends up to 3,00o ft., has a gentle gradient, and is a great belt of volcanic products. It is densely populated and of luxuriant fer tility (vine, olive, fruit, vegetables, corn, etc.), and often yields five harvests a year. On it are the towns Catania, Nicolosi and Acireale. The middle zone "regione boscosa" has a gradient of 1 in 5 and is no longer rich in oak plantations as at one time but now grows abundant pine, genista broom, chestnut, beech and ferns. The highest and central zone "regione deserta" is a desolate region of lava flows and volcanic ash, almost destitute of vegeta tion. There is a narrow zone of sub-Alpine shrubs, but no true Alpine flora. In the last 2,000 ft. five phanerogamous species onl) are to be found, the first three of which are peculiar to the mountain : Senecio Etnensis, Anthemis Etnensis, Robertsia taraxa coides, Tanacetum vulgare and Astragalus siculus. No trace of animal life is to be found in this zone ; for the greater part of the year it is covered with snow, but by the end of summer this has almost all melted, except for that preserved i:. the covered pits for use in Catania and elsewhere. The ascent is best undertaken in summer or autumn, 7 to 8 hours being required from Nicolosi. Thucydides mentions eruptions in the 8th and 5th centuries B.C. The activity comprises three periods :—prehistoric, before 70o B.C., early historic, from 70o B.C. until the i6th century and the his toric period from that time. During the historic period eruptions have taken place at intervals of approximately 6 years.
Geologically, Etna is a large volcanic cone which stands in a great Pliocene subsidence bay of the Ionian Sea. It is in contact with Tertiary sedimentary rocks in the north-west. Here occur grey Eocene and yellow and red Miocene sandstones and lime stones with Pliocene marine marl and plastic clay. These latter entirely compose the floor of the platform upon which the volcanic pile has been built up. Near the coast ancient lava flows overlie Pleistocene conglomerates and gravels, thus proving that the sub aerial activity did not begin until middle Quaternary times. The volcanic rocks consist of crystalline and vitreous lavas and tuffs, essentially basaltic in composition, largely porphyritic and wholly non-leucitic. Other types are augite and phonolitic andesites and labradorite rock. The andesites were the earliest erupted rocks. Basic plagioclase felspar and augite are the most common minerals, olivine being very subordinate or missing altogether. The constancy of composition indicates derivation from a remark ably uniform magma. At Acireale the lava has assumed the pris matic or columnar form in a striking manner; at the rock of Aci it is in parts spheroidal. The Grotte des Chevres has been regarded as an enormous gas-bubble in the lava. The remarkable stability of the mountain appears to be due to the innumerable dykes which penetrate the lava flows and tuff beds in all directions and thus bind the whole mass together.
From the earliest times the mountain has naturally been the subject of legends. The Greeks believed it to be either the moun tain with which Zeus had crushed the giant Typhon (so Pindar, Pyth. i. 34 seq.; Aeschylus, Prometheus Vinctus, 351 seq.; Strabo xiii. p. 626), or Enceladus (Virgil, Georg. i. 471; Oppian, Cyn. i. 273), or the workshop of Hephaestus and the Cyclopes (Cic. De divin. ii. 19; cf. Lucil., Aetna, 41 seq., Solin, I I) . Several Roman writers, on the other hand, attempted to explain the phe nomena which it presented by natural causes (e.g., Lucretius vi. 639 seq.; Lucilius, Aetna, 51I seq.). Ascents of the mountain were not infrequent in those days—one was made by Hadrian.
In Nov. 1928 grave consternation was caused by the renewed activity of Etna. The Messina-Catania railway line was blocked by the streams of lava ioo ft. wide descending from the crater at an average speed of 20 ft. a minute. On Nov. 7 the lava reached the sea. The town of Mascati was completely wiped out and the village of Nunziatg. almost entirely destroyed. The loss was estimated at £ 2,000,000.