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VESUVIUS (also Vesevus in ancient poets), a volcano rising from the eastern margin of the Bay of Naples in Italy, about 7 m. E.S.E. of Naples, in the midst of a region which has been densely populated by a civilized community for more than twenty-five centuries. Hence the mountain has served as a type for the general popular conception of a volcano, and its history has supplied a large part of the information on which geological theories of volcanic action have been based. The height of the mountain varies from time to time within limits of several hundred feet, according to the effects of successive eruptions, but averages about 4000 ft. above sea-level (in June 1900, 4275 ft., but after the eruption of 1906 considerably less). Vesuvius consists of two distinct portions. On the northern side a lofty semicircular cliff, reaching a height of 3714 ft., half encircles the present active cone, and descends in long slopes towards the plains below. This precipice, known as Monte Somma, forms the wall of an ancient prehistoric crater of vastly greater size than that of the present volcano. The continuation of the same wall round its southern half has been in great measure obliterated by the operations of the modern vent, which has built a younger cone upon it, and is gradually filling up the hollow of the prehistoric crater. At the time of its greatest dimensions the volcano was perhaps twice as high as it is now. By a colossal eruption, of which no historical record remains, the upper half of the cone was blown away. It was around this truncated cone that the early Greek settlers founded their little colonies.

At the beginning of the Christian era, and for many previous centuries, no eruption had been known to take place from the mountain, and the volcanic nature of the locality was perhaps not even suspected by the inhabitants who planted their vine- yards along its fertile slopes, and built their numerous villages and towns around its base. The geographer Strabo, however, detected the probable volcanic origin of the cone and drew attention to its cindery and evidently fire-eaten rocks. From his account and other references in classical authors we gather that in the first century of the Christian era, and probably for hundreds of years before that time, the sides of the mountain were richly cultivated, as they are still, the vineyards being of extraordinary fertility. The wine they produce is known as Lacrimae Ckristi. But towards the top the upward growth of vegetation had not concealed the loose ashes which still remained as evidence of the volcanic nature of the place. On this barren summit lay a wide flat depression, surrounded with rugged walls of rock, which were festooned with wild vines. The present crater-wall of Monte Somma is doubtless a relic of that time. It was in this lofty rock-girt hollow that the gladiator Spartacus was besieged by the praetor Claudius Pulcher; he escaped by twisting ropes of vine branches and descending through unguarded fissures in the crater-rim. A painting found in Pompeii in 1879 represents Vesuvius before the eruption (Notizie degli scavi, 1880, pi. vii.)-

After centuries of quiescence the volcanic energy began again

to manifest itself in a succession of earthquakes, which spread alarm through Campania. For some sixteen years after 63 these convulsions continued, doing much damage to the surrounding towns. At Pompeii, for example, among other devastation, the temple of Isis was shaken into ruins, and, as an inscription records, it was rebuilt from the foundations by the munificence of a private citizen. On the 24th of August 79 the earthquakes, which had been growing more violent, culminated in a tremendous explosion of Vesuvius. A contemporary account of this event has been preserved in two letters of the younger Pliny to the historian Tacitus. He was staying at Misenum with his uncle, the elder Pliny, who was in command of the fleet. The latter set out on the afternoon of the 24th to attempt to rescue people at Herculaneum, but came too late, and went to Stabiae, where he spent the night, and died the following morning, suffocated by the poisonous fumes which were exhaled from the earth. This eruption was attended with great destruction of life and property. Three towns are known to have been destroyed-Herculaneum at the western base of the volcano, Pompeii on the south-east side, and Stabiae, still farther south, on the site of the modern Castellamare. There is no evidence that any lava was emitted during this eruption. But the abundant steam given off by the volcano seems to have condensed into copious rain, which, mixing with the light volcanic dust and ash, gave rise to torrents of pasty mud, that flowed down the slopes and overwhelmed houses and villages. Herculaneum is believed to have been destroyed by these “ water lavas, ” and there is reason to suppose that similar materials filled the cellars and lower parts of Pompeii. Comparing the statements of Pliny with the facts still observable in the district, we perceive that this first recorded eruption of Vesuvius belongs to that phase of volcanic action known as the paroxysmal, when, after a longer or shorter period of comparative tranquillity, a volcano rapidly resumes its energy and the partially filled-up crater is cleared out by a succession of tremendous explosions. For nearly fifteen hundred years after the catastrophe of 79 Vesuvius remained in a condition of less activity. Occasional eruptions are mentioned, e. g. in A.D. 203, 472 and 685, and nine in the middle ages down to 1 500. None, however, was of equal importance with the first, and their details are given vaguely by the authors who allude to them. By the end of the I 5th century the mountain had resumed much the same general aspect as it presented before the eruption described by Pliny. Its crater walls, some 5 m. in circumference, were hung with trees and brushwood, and at their base stretched a wide grassy plain, where cattle grazed and the wild boar lurked in the thickets. The central tract was a lower plain, covered with loose ashes and marked by a few pools of hot and saline water. At length, after a series of earthquakes lasting for six months and gradually increasing in violence, the volcano burst into renewed paroxysmal activity on the 16th of December 1631. Vast clouds of dust and stones, blown out of the crater and funnel of the volcano, were hurled into the air and carried for hundreds of miles, the finer particles falling to the earth even in the Adriatic and at Constantinople. The clouds of steam condensed into copious torrents, which, mingling with the fine ashes, produced muddy' streams that swept far and wide over the plains, reaching even to the foot of the Apennines. Issuing from the flanks of the mountain, several streams of lava flowed down I towards the west and south, and reached the sea at twelve or thirteen different points. Though the inhabitants had been warned by the earlier convulsions of the mountain, so swiftly did destruction come upon them that 18,000 are said to have lost their lives.

Since this great convulsion, which emptied the crater, Vesuvius has never again relapsed into a condition of total quiescence. At intervals, varying from a few weeks or months to a few years, it has broken out into eruption, sometimes emitting only steam, dust and scoriae, but frequently also streams of lava. The years 1766-67, 1779, 1794, 1822, 1872 and 1906 were marked by special activity. The last completely altered the aspect of the cone, considerably reducing its height.

The modern cone of the mountain has been built up by successive discharges of lava and fragmentary materials round a vent of eruption, which lies a little south of the centre of the prehistoric crater. The southern segment of the ancient cone, answering to the semicircular wall of Somma on the north side, has been almost concealed, but is still traceable among the younger accumulations. The numerous deep ravines which indented the sides of the prehistoric volcano, and still form av marked feature on the outer slopes of Somma, have on the south side served as channels to guide the currents of lava from the younger cone. But they are gradually being filled up there and will ultimately disappear under the sheets of -molten rock that from time to time rush into them from above. On one of the ridges between these radiating valleys an observatory for watching the progress of the volcano was established by the Neapolitan government, and is still supported as a national institution. A continuous record of each phase in the volcanic 'changes has been taken, and some progress has been made in the study of the phenomena of Vesuvius, and in prognosticating the occurrence and probable intensity of eruptions. The foot of the cone is reached from Naples by electric railway, and thence a wirerope railway (opened in 1880) carries visitors to within 150 yds. of the mouth of the crater.

See John Phillips, Vesuvius (1869); Pompei e la Regions Sotterrata dal Vesuvio neil' Anno 79 (Naples, 1879); L. Palmieri, Vesuvio e la sua Storia (Milan, 1880); H. J. Johnstone-Lavis, “The Geoiogy of Monte Somma, and Vesuvius” (1884), in Quart. Journ. Geal. Soc. vol. xl. p. 85; J. L. Lobley, Mount Vesuvius (London, 1889); F. Furchheim, Bibliografia del Vesuvio (Naples, 1897); Tr McK. Hughes, “Herculaneum,” in Proc. Camb. Anti. Soc. No. xlviii, p. 25 (Cambridge, 1908).