Effects of subterranean heat in the present age of the world—Vast accumulations of solid matter from the eruptions of volcanos—Buried cities of Pompeii and Herculaneum—Curious relics of Roman life—Monte Nuovo—Eruption of Jorullo in the province of Mexico—Sumbawa in the Indian Archipelago—Volcanos of Iceland—Mountain mass of Etna the product of volcanic eruptions—Volcanic islands—In the Atlantic—In the Mediterranean—Santorin in the Grecian Archipelago.

Having now sufficiently demonstrated the existence of intense subterranean heat, diffused, if not universally, at least very generally, beneath the superficial shell of the Earth, we shall next proceed to inquire if it is capable of effecting those physical changes which are ascribed to it in Geology;—of producing land where none before existed, of upheaving the solid Crust of the Earth, of driving the ocean from its bed, of dislocating and contorting solid masses of rock. The argument is still an appeal to facts. Such effects as these have been produced by the agency of internal heat, under actual observation, in the present age of the world; and it is not unreasonable to attribute to the same cause similar phenomena in ages gone by.

We will not run the risk of dissipating the force of this reasoning by attempting to expand it. It will be enough for us to state the facts: we shall leave it to our readers to estimate for themselves the value of the argument. There are three forms, more or less distinct, though closely associated, under which the subterranean fires have exerted their power in modern times to disturb and modify the Physical Geography of the Globe;—(1) the Volcano, (2) the Earthquake, (3) the gentle Undulation of the Earth’s Crust. Of these we shall speak in order.

In the case of Volcanos, as we have already sufficiently conveyed, the hidden furnaces of the Earth find a vent for their surplus energies; and when this vent is once established, that is to say, when the active Volcano has begun to exist, it seems probable that there is little further upheaval, properly so called, of the surface. Nevertheless, Volcanos contribute largely to the formation of land by the vast accumulation of ashes, mud, and lava, which they vomit forth. The destruction of Herculaneum and Pompeii is a case in point. For eight days successively, in the year 79, the ashes and pumice stone cast up from the crater of Vesuvius, fell down in one unceasing shower upon these devoted cities; while at the same time floods of water, carrying along the fine dust and light cinders, swept down the sides of the mountain in resistless torrents of mud, entering the houses, penetrating into every nook and crevice, and filling even the very wine jars in the underground cellars.

At the present moment the layers of volcanic matter beneath which Pompeii has been slumbering for centuries, are from twelve to fourteen feet over the tops of the houses. Loftier still is the pile that overlies the buried Herculaneum. This city, situated nearer to the base of the Volcano, has been exposed to the effects of many successive eruptions; and accordingly, spread out over the mass of ashes and pumice by which it was first overwhelmed, in the time of Pliny, we now find alternate layers of lava and volcanic mud, together with fresh accumulations of ashes, to a height, in many places, of 112 feet, and nowhere less than 70. Nor was this ejected matter confined to these two populous towns. It was scattered far and wide over the country around, and has contributed in no small degree to that extraordinary richness and fertility for which the soil of Naples is so justly famed.

As regards the production of land where none before existed, here is one fact of singular significance. At the time of the eruption, in 79, Pompeii was a seaport town to which merchantmen were wont to resort, and a flight of steps, which still remains, led down to the water’s edge: it is now more than a mile distant from the coast, and the tract of land which intervenes is composed entirely of volcanic tuff and ashes.

Gladly would we linger over the reminiscences of these luxurious and ill-fated cities. By the removal of the ashes, Pompeii is now laid open to view for at least one-third of its extent; and a strange sight it is, this ancient Roman city thus risen as it were from the grave,—risen, but yet lifeless,—with its silent streets, and its tenantless houses, and its empty Forum. Wherever we turn we have before us a curious and interesting picture, ghastly though it is, of the social, political, and domestic life of those ancient times, of the glory and the shame that hung around the last days of Pagan Rome;—in the theatres and the temples, in the shops and the private houses, in the graceful frescoes, in the elaborate mosaics, and, not least, in the idle scribblings on the walls, which, with a sort of whimsical reverence, have been spared by the destroying hand of Time. Then again, what a host of singular relics are there to be wondered at:—articles of domestic use and luxury, kitchen utensils and surgical instruments; female skeletons with the ornaments and vanities of the world, rings and bracelets and necklaces, still clinging to their charred remains; and strangest perhaps of all, eighty-four loaves of bread, which were put into the oven to bake 1800 years ago, and were taken out only yesterday, with the baker’s brand upon them, and the stamp of the baker’s elbow still freshly preserved in the centre of each. No subject could be more tempting to a writer, none more attractive to a reader. But our present purpose is to show the effects of Volcanos in elevating the level of the land; and so we must turn our back on the buried cities, and crossing the Bay of Naples, seek for a new illustration in the formation of Monte Nuovo, a lofty hill overlooking the ancient town of Pozzuoli.

About one o’clock at night, on Sunday, the twenty-ninth of September, 1538, flames were seen to issue from the ground close to the waters of the beautiful bay of Baiae. After a little, a sound like thunder was heard, the earth was rent asunder, and through the rent large stones, red-hot cinders, volcanic mud and volumes of water, were furiously vomited forth, which covered the whole country around, reaching even as far as Naples, and disfiguring its palaces and public buildings. The next morning it was found that a new mountain had been formed by the accumulation of ejected matter around the central opening. This mountain remains to the present day, and is called the Monte Nuovo. In form it is a regular volcanic cone, four hundred and forty feet high, and a mile and a half in circumference at its base, with an open crater in the centre, which descends nearly to the level of the sea. An eye-witness who has left us a minute account of this eruption, relates that on the third day he went up with many people to the top of the new hill, and looking down into the crater, saw the stones that had fallen to the bottom, “boiling up just as a caldron of water boils on the fire.” The same writer informs us—and it is very much to our present purpose to note the fact—that immediately before the eruption began, the relative position of land and sea was materially changed, the coast was sensibly upraised, the waters retired about two hundred paces, and multitudes of fish were raised high and dry upon the sand, a prey to the inhabitants of Pozzuoli.92

The Monte Nuovo is but a type of its class. If we travel westward 8,000 miles from Naples to the more stupendous Volcanos of the New World, we may witness the same phenomena on a still grander scale. In the province of Mexico, there is an elevated and extensive plain called Malpais, where for many generations the cotton plant, the indigo, and the sugar-cane, flourished luxuriantly in a soil richly endowed with natural gifts, and carefully cultivated by its industrious inhabitants. Everything was going on as usual in this smiling and prosperous region, and no one dreamed of danger, when suddenly, in the month of June, 1759, subterranean sounds were heard, attended with slight convulsions of the earth. These symptoms of internal commotion continued until the month of September, when they gradually died away, and tranquillity seemed to be restored. But it was only the delusive lull that precedes the fury of the storm. On the night of the twenty-eighth of September the rumbling sounds were heard again more violent than before. The inhabitants fled in consternation to a neighboring mountain, from the summit of which they looked back with wonder and dismay upon the utter annihilation of their homesteads and their farms. Flames broke out over an area half a square league in extent, the earth was burst open in many places, fragments of burning rock were thrown to prodigious heights in the air, torrents of boiling mud flowed over the plain, and thousands of little conical hills, called by the natives Hornitos or Ovens, rose up from the surface of the land. Finally a vast chasm was opened, and such quantities of ashes and fragmentary lava were ejected as to raise up six great mountain masses, which continued to increase during the five months that the eruption lasted. The least of these is 300 feet high, and the central one, now called Jorullo, which is still burning, is 1600 feet above the level of the plain. When Baron Humboldt visited this region just forty years after the eruption had ceased, the ground was still intensely hot, and “the Hornitos were pouring forth columns of steam twenty or thirty feet high, with a rumbling noise like that of a steam boiler.”93 Since that time, however, the face of the country has become once more smiling and prosperous; the slopes of the newly-formed hills are now clothed with vegetation, and the sugar-cane and the indigo again flourish luxuriantly in the fertile plains below.

On the opposite side of the Globe, 10,000 miles from Mexico, we have had, almost in our own time, an exhibition of volcanic phenomena not less wonderful than those we have been describing. The island of Sumbawa lies about two hundred miles to the east of Java in the Indian Archipelago; and it belongs to that remarkable chain of Volcanos which we have already described as stretching, with little interruption, along the coast of Asia from Russian America to the Bay of Bengal. In the year 1815, this island was the scene of a calamitous eruption, the effects of which were felt over the whole of the Molucca Islands and Java, as well as over a considerable portion of Celebes, Sumatra, and Borneo. Indeed, so extraordinary are the incidents of this eruption, that we might well hesitate to believe them if they had not been collected on the spot with more than ordinary diligence, and recorded with an almost scrupulous care. Sir Stamford Raffles, who was at the time governor of Java, then a British possession, required all the residents in the various districts under his authority to send in a statement of the circumstances which occurred within their own knowledge; and from the accounts he received in this way, combined with other evidence, chiefly obtained from eye-witnesses, he drew up the narrative to which we are mainly indebted for the following facts.

The explosions which accompanied this eruption were heard in Sumatra, at a distance of 970 geographical miles; and in the opposite direction at Ternate, a distance of 720 miles. In the neighborhood of the Volcano itself, immense tracts of land were covered with burning lava, towns and villages were overwhelmed, all kinds of vegetation completely destroyed, and of 12,000 inhabitants in the province of Tomboro, only twenty-six survived. The ashes, which were ejected in great quantities, were carried like a vast cloud through the air, by the southeast monsoon, for 300 miles in the direction of Java; and, still farther to the west, we are told that they formed a floating mass in the ocean two feet thick and several miles in extent, through which ships with difficulty forced their way. It is recorded, too, that they fell so thick on the island of Tombock, 100 miles away, as to cover all the land two feet deep, destroying every particle of vegetation, insomuch that 44,000 people perished of the famine that ensued. “I have seen it computed,” writes Sir John Herschel, “that the quantity of ashes and lava vomited forth in this awful eruption would have formed three mountains the size of Mont Blanc, the highest of the Alps; and if spread over the surface of Germany, would have covered the whole of it two feet deep.” Finally, it appears that this eruption was accompanied, like that of Monte Nuovo, by a permanent change in the level of the adjoining coast; in this case, however, it was a movement, not of upheaval, but of subsidence: the town of Tomboro sunk beneath the ocean, which is now eighteen feet deep where there was dry land before.94

Once more we will ask our readers to take a rapid flight over the map of the world, passing, this time, from the Indian Archipelago to the island of Iceland,—that “wonderful land of frost and fire.” Besides the famous Volcano of Hecla, there are five others scarcely less formidable, all of which have been in active eruption within modern times. Of these the most celebrated is that of Skaptar Jokul. In the year 1783, this Volcano poured forth two streams of lava, which, when hardened, formed together one continuous layer of igneous rock, ninety miles in length, a hundred feet in height, and from seven to fifteen miles in breadth. The phenomena which accompanied the eruption are thus vividly described by Sir John Herschel:—“On the tenth of May innumerable fountains of fire were seen shooting up through the ice and snow which covered the mountain; and the principal river, called the Skapta, after rolling down a flood of foul and poisonous water, disappeared. Two days after, a torrent of lava poured down into the bed which the river had deserted. The river had run in a ravine 600 feet deep and 200 broad. This the lava entirely filled; and not only so, but it overflowed the surrounding country, and ran into a great lake, from which it instantly expelled the water in an explosion of steam. When the lake was fairly filled, the lava again overflowed and divided into two streams, one of which covered some ancient lava fields; the other re-entered the bed of the Skapta lower down, and presented the astounding sight of a cataract of liquid fire pouring over what was formerly the waterfall of Stapafoss. This was the greatest eruption on record in Europe. It lasted in its violence till the end of August, and closed with a violent earthquake; but for nearly the whole year a canopy of cinder-laden cloud hung over the island: the Faroe Islands, nay, even Shetland and the Orkneys, were deluged with ashes; and volcanic dust and a preternatural smoke which obscured the sun, covered all Europe as far as the Alps, over which it could not rise. The destruction of life in Iceland was frightful: 9,000 men, 11,000 cattle, 28,000 horses, and 190,000 sheep perished; mostly by suffocation. The lava ejected has been computed to amount in volume to more than twenty cubic miles.”95

With these very significant facts before us, it is hard to resist the conclusion that the great mountain mass of Etna, 11,000 feet high and ninety miles in circumference, is formed entirely of volcanic matter ejected during successive eruptions. For the whole mountain is nothing else than a series of concentric conical layers of ashes and lava, such as have been poured out more than once upon its existing surface in modern times. Just, then, as Monte Nuovo was produced by an outburst of volcanic power in a single night, and the far larger mountain of Jorullo in the course of a few months, so may we believe that the more stupendous Etna is the work of the same power operating through a period of many centuries. And applying this conclusion to many other mountains throughout the world of exactly the same structure, we come to form no very mean estimate of the permanent changes wrought on the physical geography of our Globe by the operations of volcanic agency.

We must remember, too, that volcanic eruptions are not confined to the land; they often break out in the bed of the sea. In such cases the waters are observed in a state of violent commotion, jets of steam and sulphurous vapor are emitted, light scoriaceous matter appears floating on the surface, and not unfrequently the volcanic cone itself slowly rises from the depths below, and continues to grow from day to day, until at length it becomes an island of no inconsiderable magnitude. Sometimes when the violence of the eruption has subsided, the new island, consisting chiefly of ashes and pumice-stone, is gradually washed away by the action of the waves; but in the other cases, these lighter substances are compacted together by the injection of liquid lava, and being thus able to withstand the erosive power of the ocean, assume the importance of permanent volcanic islands. Many examples of the former kind are recorded within the last hundred years. In 1783 an island was thrown up in the North Atlantic Ocean, about thirty miles to the southwest of Iceland. It was claimed by the King of Denmark, and called by him NyÖe or New Island; but before a year had elapsed, this portion of his Majesty’s dominion disappeared again beneath the waves, and the sea resumed its ancient domain. A cone-shaped island of the same kind, called Sabrina, three hundred feet high, with a crater in the centre, appeared amongst the Azores in 1811, but was quickly washed away again.

A more interesting example, because the circumstances are more minutely recorded, is the island which made its appearance in the Mediterranean, off the southwest coast of Sicily, in the year 1831. During its brief existence of three months, it received from contemporary writers seven different names; but the name of Graham Island seems to be the one by which it is most likely to be known to posterity. “About the tenth of July,” writes Sir Charles Lyell, “John Corrao, the captain of a Sicilian vessel, reported that, as he passed near the place, he saw a column of water like a waterspout, sixty feet high, and eight hundred yards in circumference, rising from the sea, and soon afterward a dense steam in its place, which ascended to the height of 1800 feet. The same Corrao, on his return from Girgenti, on the eighteenth of July, found a small island, twelve feet high, with a crater in the centre, ejecting volcanic matter and immense columns of vapor; the sea around being covered with floating cinders and dead fish. The scoriae were of a chocolate color, and the water, which boiled in the circular basin, was of a dingy red. The eruption continued with great violence to the end of the same month, at which time the island was visited by several persons, and amongst others by Captain Swinburne, R. N., and M. Hoffman, the Prussian Geologist.”96 By the fourth of August the new island is said to have attained a height of 200 feet, and to have been three miles in circumference. Yet this was nothing more than the top of the volcanic cone; for, a few years before, Captain W. H. Smyth, in his survey, had found a depth of 600 feet at this very spot; and therefore the total height from the base of the mountain must have been 800 feet. From the beginning of August it began to melt away; and at the commencement of the following year, nothing remained of Graham Island but a dangerous shoal.

But even of the islands that occupy a prominent place on the map of the world, there is not wanting evidence to show that a large number derive their origin from the action of volcanic power. Among these may be mentioned many of the Molucca and Philippine groups, also several in the Grecian Archipelago, and not a few of the Azores and the Canaries,—in particular the lofty peak of Teneriffe, rising 12,000 feet above the level of the sea. In some cases, indeed, the actual process of their birth, and of their subsequent growth and development, has been minutely observed. A remarkable example occurs among the Aleutian Islands already referred to. In the year 1796 a column of smoke was seen to issue from the sea; then a small black point appeared at the surface of the water; then flames broke out, and other volcanic phenomena were exhibited; then the small black point grew into an island, and the island increased in size until it was at last several thousand feet high, and two or three miles in circumference. And such it remains to the present day.

Fig. 28.—Bird’s-eye view of Santorin during the volcanic eruption of February, 1866. (Lyell.)

a. Therasia.
b. The northern entrance, 1068 feet deep.
c. Thera.
d. Mount St. Elias, rising 1887 feet above the sea.
e. Aspronisi.
f. Little Kaimeni.
g. New Kaimeni.
h. Old Kaimeni.
i. Aphroessa.
k. George.