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wol,CANIC ERUPTIONS. 245
ground, increase, and the whole neighborhood gives evidence of the immense pressure which is being exerted; presently the molten lava, is by the immense force raised into the crater, and filling it up, or melting its passage through the side, flows in a red hot stream down the flanks of the mountain in a river, or rather a torrent of fire. The eruption is sometimes attended with enormous currents of water, mud, and noxious gasses. A period of rest succeeds, generally of short duration; again the same phemomena are repeated, and thus the action continues for a variable length of time, until finally, the crisis is past and the volcano resumes its original quiet. The substances principally ejected by volcanoes are smoke, ashes, sand, scoriae, volcanic glass and bombs, and masses of rock. The ashes thrown out in volcanic eruptions appear to be the substance of the lava very finely divided. These ashes are raised so high that they are carried by the winds to almost incredible distances. Ashes from the eruption of a volcano in St. Vincent in 1812, were carried twenty leagues, and fell in Barbadoes, and from the eruption of Hecla in 1766, they fell in Glaumba, a distance of fifty leagues; and it is said that ashes from Vesuvius have fallen in Constantinople, a distance of four hundred and fifty leagues. The volcanic sand, is composed of particles somewhat larger, but of the same character as the ashes, being commimuted particles of lava, and forming a principal part of the eject, ed matter of volcanic eruptions. Scoriae, and pumice stone, are caused by the gasses, which bursting through the melted lava, carry up with them certain portions into the atmosphere, which becoming consolidated, present the appearance so well known under the name of slag and cinders. Volcanic glass or obsidian, is often ejected in small melted masses; sometimes, the winds catching this, spin it into the finest threads. We have seen many specimens of this kind from the eruptions of Kirauea, in the Sandwich Islands. Among the extinct volcanoes of France, drops, tears, and elongated spheroids, being drops of lava thrown out, and consolidated in the air, are continually found, they are called volcanic bombs. Masses of rock are always ejected in severe eruptions; in many cases these are undoubtedly torm off
from the interior of the mountain by the immense power exerted; and they are ejected without having been melted. A stone of 109 cubic yards in volume, was ejected by Cotopaxi, and thrown to a distance of nine miles.
The force which is exerted, to cause the eruptions of lavas, or liquid masses of stone, is almost beyond belief, varying according to the height of the crater. The force of Vesuvius in some of its eruptions has been estimated as equivalent to a pressure of at least 6000 pounds on every square inch ; and of Etna, about 17,000 pounds on the square inch ; the amount of force requisite to raise melted lava to the crater of Cotopaxi, would be at least 30,000 pounds on each square inch. The masses of melted matter ejected, are equally incredible; the amount thrown out by Vesuvius in 1737, was estimated at 11,839,168 cubic yards, and about twice this amount in 1794. In 1660, the mass of matter disgorged by Etna, according to Mr. Lyell, was twenty times greater than the whole mass of the mountain, and in 1669, when 77,000 persons were destroyed, the lava covered 84 square miles. The greatest eruption of modern times, was from Skaptar Jokul, in Iceland, in 1783. Two streams of lava, one fifty miles long and twelve broad, the other forty miles long, and seven broad; both avaraging 100 feet in thickness, and sometimes 500 or 600 feet, flowed in opposite directions, destroying twenty villages, and 9000 inhabitants. The velocity with which the melted lavas move varies with the slope of the mountain, and the nature of the ground, as well as the viscidity and quantity of the lava. In general, a velocity of 400 yards an hour is considered quick, although sometimes the stream flows much quicker; in flat grounds it sometimes occupies whole days in moving a few yards. Lavas cool extremely slow, the surface becomes soon consolidated, and is such a poor conducter of heat, that the interior remains heated and melted for whole years; and currents have been mentioned which were flowing ten years after emerging from the crater, and they have been seen smoking twenty years after an eruption of Etna. The currents of lava thrown out by successive eruptions being placed one above the other, alternating with beds of sand, scoriae, &c., form a series of inclined beds that give rise to the cone of the mountain.
HERCULAN EUM AND POMPEii. 247
Having now described the principal phenomena attending volcanic eruptions, and the nature of the erupted materials, we proceed to describe briefly some of the more remarkable effects of volcanic agency. Southern Italy, being inhabited by a cultivated people, and in very early times the seat of literature and science, as well as the grand European seat of volcanic action, claims particular attention. IIere are three active volcanic vents. Wesuvius near Naples, Stromboli on the Lipari Isles, and Etna in Sicily. The whole region is subject to earthquakes, and abounds in thermal springs impregnated with calcareous matter, and from certain fissures deleterious gasses and sulphureous flames issue. The ancient name of Vesuvius, was Somma; it is now a broken and irregular coue about 4000 feet in height. We have already given the description of this mountain as it appeared before the eruption of 1631. It is said that its cone was formerly of a regular shape, with a flat summit, containing the remains of an ancient crater, and covered with wild vines. After a slumber of ages, Vesuvius in the year 63, began to exhibit some symptoms of internal agitation, by an earthquake which occasioned considerable damage to some of the neighboring cities. It is somewhat remarkable that the memorials of this convulsion have been preserved, and made known, through the agency of another more terrible convulsion, that of August 24th in the year 79, when a tremendous eruption occurred, and the pent up melted materials of the volcano burst out, overwhelming three cities and many of their inhabitants. Two of these cities, Herculaneum, and Pompeii, have since been exhumed. The former was first discovered ; but they had long been forgotten. The eruption which destroyed these cities was witnessed by both the Plinys, and indeed, it was from his too venturesome curiosity to observe this magnificent natural exhibition, that the elder Pliny lost his life, being suffocated by the sulphureous vapors. The account which Pliny the Younger has left of this eruption, is very full and minute ; but he makes no allusion to the overwhelming of the two cities. In 1713, Herculaneum was accidentally discovered, having been buried in lava for 1634 years. Some flagments of imarble were observed in sinking a well; and subsequently a small temple, and some statuary. The city of Portici is built upon the lava directly above Herculaneum, and this has prevented extensive excavations. Pompeii was enveloped in ashes and cinders, and has been opened to the light of day. “Both these cities were sea-ports, and Herculaneum is still near the shore, but Pompeii is at some distance, the intervening land having been formed by volcanic agency. In both these cities inscriptions were found in the temples commemorating the event of their rebuilding after having been overthrown by an earthquake sixteen years before, A. D. 63. Thus, in the language of Bulwer, “After nearly seventeen centuries had rolled away, the city of Pompeii was disintered from its silent tomb, all vivid with undimmed hues; its walls fresh as if painted yesterday; not a tint faded on the rich mosaic of its floors; in its forum the half-finished coluwans, as
left by the workman's hand; before the trees in its gardens the sacrificial tripod; in its halls the chest of treasure; in its baths the
strigil; in its theatres the counter of admission; in is saloons the furniture and the lamp; in its triclinia the fragments of the last feast; in its cubicula the perfumes and rouge of faded beauty;
and everywhere the skeletons of those who once moved the
springs of that minute, yet gorgeous machine of luxury and of life.”
ERUPTIONS OF ETNA. 249
peiana, showing the site of Pompeii, and the course of the river Sarnus. Among the ruins of these cities many valuable relics have been found. The various utensils and works of art, almost as fresh as though buried but for a day. Rolls of papyri, with little tickets attached, denoting their contents; loaves bearing the stamp of the baker; linen, and fish-nets, and fruits, all preserved along with sculptures, and paintings, and unharmed for near 2000 years. No doubt, many valuable manuscripts will be found when Herculaneum is more excavated, which will restore to us the lost writings of the ancient philosophers. The eruption of Vesuvius which buried these cities, is so well known We need not dwell longer upon it here; we pass to consider next the eruptions of Etna. The cone of Etna, which has been so minutely and well described by Mr. Lyell, is entirely composed of lavas, and rises majestically to an altitude of two miles, the circumference of its base being about 180 miles. At the base of the mountain is a delightful, well cultivated and fertile country, thickly inhabited, and covered with olives, vines, corn, fruit trees, and aromatic herbs. Higher up, upon the mountain side, a woody belt encircles it, forming an extensive forest of chesnut, oak, and pine, with some groves of cork and beech, and affording excellent pasturage for flocks; still higher up, is a bleak barren region, covered with dark lavas and scoriae. Here, from a kind of plain arises the cone of Etna to the height of 11,000 feet, and continually emits sulphureous vapors; its highest points being covered with eternal snow. Over the flanks of Etna a multitude of minor cones are distributed, particularly in the woody tract, caused by former eruptions, but the grandest feature of Etna is the Val del Bovć, which is a vast excavation, as though a portion of the mountain had been removed on the side towards the sea, forming a vast plain, five miles across, encircled by minor volcanic cones, and enclosed on three sides by precipitous rocks from 2000 to 3000 feet high. This vast plain has been repeatedly deluged by streams of lava, and presents a surface more rugged and uneven than that of the most tempestuous sea. From the earliest period of history, Etna appears to have been active, but the first great