You have no doubt often heard of Volcanoes and Earthquakes, for almost everybody in all ages has felt a deep interest in them, and a curiosity to know what they are caused by. If you will listen to me, while I merely describe them as they really exist, without "drawing the long bow," as people say, I will then tell you how I think they are produced. It is quite certain that there is an important connexion between Volcanoes and Earthquakes; and we may safely take this for granted, and at once call the cause of both, whatever it may be, volcanic agency. It has been discovered by extensive observations, These tracts are called Volcanic bands; one of them extends nearly parallel with the West Coast of South America, along the chain of mountains called the Andes, which you will see marked on the map; and another much smaller extends from Mount Vesuvius to Mount Etna, with the Volcanic Island Stromboli, and several extinct Volcanoes lying between them, and then turns to the East, through several of the Greek Islands, and passes on to Syria, where Earthquakes are frequent. Earthquakes in their simplest form are nothing more than violent shakings of the ground; but sometimes the earth is split open; sometimes it is raised; and sometimes it is depressed. I shall tell you of some of the changes which took place in the great Earthquake of Calabria, which lies in the smaller volcanic band I mentioned to you between Vesuvius and Etna. The shocks began in 1783, and lasted for nearly four years, till the end of 1786. During this time the King of Naples sent persons to take correct notes and representations of all that was going on, and we have therefore got a better account of it than we have of any other Earthquake that ever occurred. The convulsion of the earth, sea, and air, extended as far as Naples, and over the whole of Sicily; but the district over which it was so violent as to excite intense alarm, was about five hundred miles in circumference. "The first shock of February 5th, 1783, threw down, in two minutes, the greater part of the houses in all the cities, towns, and villages, from At Messina in Sicily, the shore was rent; and the soil along the port, which before the shock was perfectly level, was inclined towards the sea, and the sea itself was considerably deeper, which showed that the inclination must have been occasioned by the bottom's sinking. The quay also sunk down 14 inches below the level of the sea, and the houses in the neighbourhood were much cracked. In one town there was a large round tower of great strength, which was divided by a perpendicular rent, and one-half was raised up several feet, so as to show the foundations. Those who saw it, said that it looked like a great tooth half extracted, showing the fangs. Along the line of the crack, the walls were found to fit so exactly There was a very curious difference between some of the walls which had been thrown down, or very much shaken by some of the shocks. In some of them, the separate stones were parted from the mortar, so as to leave an exact mould where they had rested; and in others, the mortar was ground to dust between the stones. It was not less strange to see the effect of what must have been whirling movements in the ground. In "It appears evident that a great part of the rending and splitting of the ground was the effect of a violent motion from below upwards; and in a multitude of cases where the rents and chasms opened and closed alternately, we must suppose that the earth was by turns heaved up, The district called Jerocarne, was torn in a surprising manner, and in one spot the cracks "In the vicinity of Oppido, the central point from which the earthquake diffused its violent movements, many houses were swallowed up by the yawning earth, which closed immediately over them. In the adjacent district also of Cannamaria, four farm-houses, several oil-stores, and some spacious dwelling-houses were so completely engulphed in one chasm, that no vestige of them was afterwards discernible." Amongst the many fissures that were opened, there was one, a mile long, a hundred feet wide, and thirty feet deep; and another, three quarters of a mile long, one hundred and fifty feet wide, and one hundred feet deep; and a third, about a quarter of a mile long, which was two hundred and twenty-five feet deep. A mountain was cleft completely in two; and a lake of considerable size was formed by the opening of this great chasm, and springs bursting out at the bottom. The inhabitants of the neighbourhood were afraid that the pool of nearly stagnant water which was thus formed would injure their health, and were at great expense in trying to drain it; but it was all in vain, for the springs that fed it at the bottom were inexhaustible. A great mass of earth, or hill, two hundred feet high, and four hundred feet in diameter, was moved nearly four miles out of its place, with trees growing upon it; and another similar mass, with a house on it, which was not at all "Great agitation was frequently observed in the bed of the sea during the shocks, and, on those parts of the coast where the movement was most violent, all kinds of fish were taken in greater abundance, and with much greater facility. Some rare species, which usually lie buried in the sand, were taken on the surface of the waters in great quantity. The sea is said to have boiled up near Messina, and to have been agitated as if by a copious discharge of vapours from its bottom. The Prince of Scilla had persuaded a great part of his vassals to betake themselves to their fishing-boats for safety, and he himself had gone on board. On the night of the 5th of February, when some of the people were sleeping in the boats, and others on a level plain, slightly elevated above the sea, the earth There is a fine description of the Earthquake and this melancholy result, in Cowper's Task, which we shall quote. Alas for Sicily! rude fragments now Lie scatter'd where the shapely column stood. Her palaces are dust. In all her streets The voice of singing and the sprightly chord Are silent. Revelry, and dance, and show Suffer a syncope and solemn pause; While God performs upon the trembling stage Of his own works his dreadful part alone. The rocks fall headlong, and the valleys rise, The rivers die into offensive pools, And charged with putrid verdure, breathe a gross And mortal nuisance into all the air. What solid was, by transformation strange, Grows fluid; and the fix'd and rooted earth, Tormented into billows, heaves and swells, Or with vortiginous and hideous whirl Sucks down its prey insatiable. Immense The tumult and the overthrow, the pangs And agonies of human and of brute Multitudes, fugitive on every side, And fugitive in vain. The sylvan scene Migrates uplifted; and, with all its soil Alighting in far distant fields, finds out A new possessor, and survives the change. Ocean has caught the frenzy, and upwrought To an enormous and o'erbearing height, Not by a mighty wind, but by that voice Which winds and waves obey, invades the shore With force resistless. Where now the throng, That press'd the beach, and, hasty to depart, Look'd to the sea for safety? They are gone, Gone with the refluent wave into the deep— A prince with half his people! You will find a great many other astonishing effects of this Earthquake described in Mr. Lyell's Work on Geology, from which I have extracted some parts of the preceding account. The word Volcano comes from Vulcan, the name of the God of fire in the Greek mythology. You have read how the poets used to represent him as engaged underground in forging thunderbolts for Jupiter, and other work of the same kind, with the assistance of his one-eyed journeymen the Cyclopes. They feigned that Volcanoes were the chimneys of his workshops, and that when an eruption took place he was busy forging his iron. Others pretended that when Jupiter had overcome the giants named Titans, who had rebelled against him, instead of putting them in the stocks, he placed mountains upon them, and that when the imprisoned monsters turned themselves from one side to the other, earthquakes and eruptions were the consequence. However, we don't believe any of these stories now, neither perhaps did the ancients. But you They are openings in the surface of the earth, from whence ignited matter of various kinds, smoke, and ashes, are sent forth by some subterranean agency. For the most part they do not always keep in activity, but have long intervals of rest for months, and sometimes for very many years, between the eruptions. One of the few that always keeps in eruption, is Stromboli, one of the Lipari Islands off the coast of Sicily, which there is good reason to think, has been active for nearly 1600 years. This Volcano is merely a mountain or rock, standing out of the sea, and the melted matter, that occasionally runs down its sides, flows directly into the water, and at once kills and parboils the fish that happen to be near it, and they are thus sometimes taken and eaten by the poor The way in which an eruption takes place in a Volcano of the other kind, when it has been quiet for a long time, is as follows. Great noises are heard about the foot of the mountain, and earthquakes frequently occur for several days before any change is seen in the opening or crater, as it is called. The springs in the neighbourhood often disappear, and as you may suppose all these forebodings make the people who live near gloomy enough. After a time a dreadful burst takes place, and the crater is in an instant cleared of the stones and earth that may have fallen into it during the period of repose; ashes and cinders, rocks and stones, are thrown up to an immense height in the air, and a great cloud of smoke and steam accompanies them. In perfectly still weather, this vapour is seen to shape itself in a very beautiful manner. The immense impulse from beneath sends it up to a As the eruption goes on the cloud of smoke which is always copiously charged with electricity, sends out brilliant lightnings; its form becomes disturbed, and the dark volumes of vapour are angrily sent forth in shapeless masses. Red-hot stones are sent into the air to a stupendous height; the melted matter boils up inside the crater and rolls down the sides of the mountain, setting fire to the trees that it meets with, and destroying or enveloping whatever else remains in its way. You will see their effect as they appear by night, in the other plate. I should tell you that the Volcano represented in both the pictures is Mount Vesuvius. The melted matter that boils up in the crater, and flows down the mountain, is called Lava. I dare say most of you have seen some pieces of this substance when polished and worked into ornaments. It is found in great variety, and is sometimes black, porous, and light like cinders; sometimes it consists of crystallized particles of quartz, felspar, and other minerals, so as closely to resemble granite; and not unfrequently it is a solid dark-coloured mass, heavy and hard as the stone that our streets are paved with. It issues from the crater in a melted state, bubbling and boiling like water in a tea-kettle, but you must not therefore suppose that it runs down the declivity of the mountain like water. On the contrary, its motion is mostly very slow, seldom being faster when it gets at some distance from the crater, than four miles an hour, which is about as fast as a man can walk. When it has run still further from its source it does not travel more than a few yards in a day. The motion of a stream of Lava is very peculiar, for the surface exposed to the air is immediately In this way a current will sometimes go drawling on for months after the eruption which gave rise to it has ceased. A very curious effect is produced when the lava runs in a certain state of fluidity down a steep descent. A thick, strong crust forms on the outside, and it is one of the qualities of lava when it has become hard, like most other stony substances, to present great opposition to the passage of heat. In consequence of this the liquid lava in the inside of the current is kept hot, and continues to run on for a long time after the supply from the crater has ceased, and leaves the crust in the form of an arched passage. From what I have told you about lava streams, you will see that there is not much danger from them to living creatures, who may always get out of their way fast enough: but sometimes houses and even towns are enveloped in them. However, from the peculiar mode in which they travel there is often a way of preventing this, and on one occasion it was resorted to, and the town of Catania thereby saved. A current of lava from Mount Etna was making its way straight towards the town, but a body of fifty bold strong fellows went out to meet it, armed with crow bars; with these they broke great holes in the crust at the side, and thus the stream was turned into another course, and pursued its way on one side of the town. Throughout an eruption, a great quantity of dust is produced by the rubbing of the stones against each other which are thrown out from the crater, and often fall back and are thrown up again several times. This dust is driven over a great extent of country, and a gentleman whom I visited, who lived about fourteen miles from Mount Vesuvius, told me that during the great eruption of 1822, But in more violent eruptions they are carried much further than this. In an eruption of a Volcano in Sumbawa, an island which lies some miles to the East of Java, the ashes were carried to a distance of 270 miles in such quantities as to darken the air, and in another direction they were found 300 miles off. They fell so heavily 40 miles away from the Volcano that they broke into many houses, and rendered them uninhabitable. Quantities of liquid lava are thrown upwards, and shape themselves into nearly the forms of fish by their passage through the air. These are called bombs by the inhabitants, and the fall of them is very justly dreaded, as they come with great violence. The size of the largest of those from which the following picture was taken, was six inches long, two inches and a quarter wide, and one If you should have a chance of examining any of these, you may observe how wisely the living principle, which gives the figure to fish, has been ordained by their Creator to provide the best form to assist their motions, in a medium in which they are suspended, and do not move on ground as the beasts do; seeing that it is precisely the same sort of figure as the laws of inanimate matter impress upon it, when in a yielding state, and being impelled to move under similar circumstances. I must give you a notion of the quantity of lava sometimes sent out in a single eruption. The Volcano called Skapta Jokul, in Iceland, in the year 1794, sent out two great streams, one of which was 50 miles in length, from 10 to 15 in breadth, and the ordinary depth about 100 feet, but in some deep valleys it was more than These streams were not cold in the year 1805, eleven years after they had issued from the earth, so that you may judge how long the hardened lava keeps in the heat. During the eruption in which this immense mass of melted matter was thrown out, twenty villages were destroyed, more than nine thousand persons killed, and an immense number of cattle. The vapour which rises at first in immense clouds, when the eruption slackens, or when it gets out of the reach of the heat, condenses, and mingled with the dust thrown up with it, forms mud, which rushes in torrents down the mountain. These streams of mud are called alluvions, and are very much more dreaded by the inhabitants than the lava streams, because they are so much quicker in their movement. It was one of these, and not a stream of lava There is a very remarkable Volcano in the Island of Hawaii, where Captain Cook was killed. The crater, instead of being at the top of a mountain like those of most other Volcanoes, is a large plain, seven miles in circumference, sunk below the surface of the surrounding country, and walled in by rugged cliffs more than seven hundred feet high. On this plain there are fifty-one conical hillocks, which are almost constantly sending out The islanders, before they were taught the truths of Christianity, believed it to be the abode of their deities, the chief of whom they call PelÉ, and to her, they say, that everything which grows near the Volcano is sacred. When some missionaries were going to visit it, and plucked some juicy berries from the shrubs that grew there to quench their thirst, the native guides begged them to desist till they had made an offering to PelÉ. When they got to the edge of the crater, they threw some of the berries in, and said, "PelÉ, here are your berries, and I am now going to eat some." They then ate fast enough, and were willing that the missionaries should do the same. The following are extracts from the account of our countryman, Mr. Stewart's visit to this terrific place. "I can compare the general aspect of the "At an inconsiderable distance from us, was one of the largest of the conical craters, whose laborious action had so greatly impressed our minds during the night, and we hastened to a nearer examination of it. On reaching its base, we judged it to be one hundred and fifty feet high, a huge, irregularly shapen, inverted "The chattering of the islanders around our cabins, and the occasional sound of voices in protracted conversation among our own number, had scarcely ceased long enough to admit of sound sleep, when the volcano again began roaring and labouring with redoubled activity. The confusion of noises was prodigiously great. These sounds were not fixed or confined to one place, but rolled from one end of the crater to the other; sometimes seeming to be immediately under us, when a sensible tremor of the ground on which we lay took place; and then again rushing to the farthest end with incalculable velocity. The whole air was filled with the tumult; and those most soundly asleep were quickly roused by it to thorough wakefulness. "At the same time a whole lake of fire opened in a more distant part. This could not have been less than two miles in circumference; and its action was more horribly sublime than anything You must know that most of the volcanic mountains bear evident traces of having been built up of matter thrown out, in the first place, from a crack or hole in the ground, and afterwards from the crater or cup, which would thus soon be formed. At every eruption a new layer of dust, and cinders, and lava, is added, and thus a mountain is gradually produced. In some instances, the successive layers may Volcanic operations can go on very nearly as well at the bottom of the sea, as upon dry land; and if you remember what I told you before, respecting the mode in which the currents of lava flow, you will not be much surprised to hear that their progress is not stopped by the water, though it may be somewhat impeded. It is certain that the streams often travel a great way at the bottom of the sea. When a Volcano breaks out under the sea, if the eruption send out a sufficient quantity of lava, and stones and dust, it gets above the surface and makes such a Volcano as Stromboli. If the Volcano should afterwards become quiet, A great many of the islands of the South Sea, and some of the Greek islands, originated in this manner; and, only two or three years ago, an island suddenly rose up off the coast of Sicily, and was taken possession of in due form by a British captain, in the name of the king of England; but, as the land consisted of loose earth, and had not much lava to bind it together, it soon sunk down, and now no trace of it is to be seen. There are many Volcanoes in Iceland, and the whole island seems to have been the produce of Volcanic agency. I am going to describe to you one of the most singular proofs of this. Geysers are springs which spout out at intervals great streams of hot water. The name is taken from the Icelandic word, geysa, which signifies, to rage, or, burst forth violently. The Icelanders are a very simple, excellent people, and exceedingly kind and hospitable to strangers. This is not the place for me to tell you how much kindness I experienced among them; but if I were to do so, you would have as high a regard for them as I have. They have in general a considerable degree of intelligence, but I was surprised to find that a great many of them did not know where the Geysers were, or anything about them. There are many springs of the same kind in several parts of Iceland; but those that are generally known as the Geysers, are near the town of Haukadal, in the south-west part of Iceland. To these I went in company with four other persons, and a guide. After a dreary ride through a wild volcanic looking country, we left our horses in a safe place, and then, proceeding some distance on foot, we saw clouds of steam arising over the hills before us. A little further on we got into the plain, where the Geysers are situated, which is The great Geyser is at the top of a hillock, which seems to have been formed in the course of years by the substances which the hot water holds in solution, and deposits as it cools. At the top of this mound we found a pond of the shape of a saucer, lined with the most curious incrustations of spar, which exactly resembled the heads of cauliflowers. It was then about half full of the most beautiful hot water, as clear as crystal, which was just stirred in gentle waves by the steam that rose up from the opening at the bottom of the basin. We took advantage of this tranquil state of the spring, to examine this opening. We let down a line, with a weight at the end, to the depth of about eighty feet, and as nearly as we could judge, it went down perpendicularly. The hole was nearly round, and about nine feet in diameter, but it got gradually wider towards the top like a funnel. The inside showed The saucer-shaped reservoir was fifty feet across, and four feet deep. I ought to tell you that the waters of the Geysers have a petrifying property, and hence the ground all around them is covered with what was once grass, moss, and sticks, converted into stone, of which we brought away many beautiful specimens. It was very late in the evening when we had completed this examination, and fixed our tent where we intended to pass the night. The springs still continued quiet, and you may judge how impatient we were for something to be going on. However, as it was dark, and we were very tired, having had a great deal of fatigue during the day, we lay down in the tent and went to sleep. About midnight we were suddenly called up The next morning, as soon as it was light, there was a beautiful eruption of the New Geyser, as it is called. The column of water was eight feet in diameter, and full sixty feet high, and the clouds of steam were prodigious. The sun was just then rising, and the effect of his rays through the water and stream, was exquisitely beautiful, producing many little rainbows. When the water had sunk down, its place was taken by a tremendous jet of spray and steam, rushing out with a deafening roar to nearly the same height as the water. When we threw some large stones into the We were not yet satisfied, because we had not seen an eruption fairly from beginning to end; so we waited some time longer. At about seven o'clock in the morning, we heard low grumbling sounds near the great Geyser, and the water in the basin bubbled up a little more actively. We then had an hour and a half of anxious expectation, during which we kept walking round the hillock; there were then about a dozen loud reports which made the earth tremble, and the water rose to near the top of the basin, and became so restless that many of the waves washed over the edge. A little while afterwards, the reports became There was then a rest for a few seconds, which was followed by several jets from forty to sixty feet high; and after them a column was thrown up eighty feet high, and ten feet in diameter. But the last jet was the most remarkable, for it was more than ninety feet high, and lasted for seven minutes. This great effort seemed to have wearied the Geyser, for the water instantly sunk down out of the basin into the pipe, quite out of sight; but in a few minutes it rose again to within a foot of the edge of the basin, and then remained stationary. Besides the great perpendicular jets, there When we were quite sure it was all over, we tried the temperature of the water in the basin, and found it to be twenty degrees cooler than before the eruption, which was probably caused by the exposure of the water which had been thrown up into the air. It seems there are generally about five or six eruptions of each of the two great Geysers, within twenty-four hours. But while we were on the spot, many of the smaller springs spouted up much oftener, and one bustling little thing darted out its waters in all directions, three or four times in an hour. We did not see any jet from the great Geyser above one hundred feet high; but some travellers have asserted that they are at times two or three hundred feet in height. It would appear Some of the water of the great Geyser falls over the edge of the basin into a deep hole in the rock below, which makes a capital warm bath, for by the time the water reaches it, it is of the desirable coolness. I can assure you, we enjoyed a bathe in it very much indeed. There are several other springs in Iceland of nearly the same character, and the most remarkable are the Hot Springs of Reykium. The largest of these has two openings, from one of which the water is incessantly flowing to the height of six or eight feet; the other opening is about ten feet distant, and is surrounded by an incrusted brim, like that of the great Geyser. The eruptions take place from this about fifteen times in twenty-four hours, to the height of about thirty feet, accompanied with a great deal of steam. There is also a most wonderful spring in Reykium, called the Badstofa. It flows into a great cave, from the bottom of which the water keeps on retreating and flowing like the waves of the sea, with a deep rumbling sound for some time before the eruption, when the water rushes up to the height of nearly twenty feet. About half a mile from this place, there are some Hot Springs that rise in the bed of a river, and force themselves quite through the cold water which covers them. There is a wonderful place in Iceland, which I am sure you would like to hear about. It is in the south-west part of the island nearer the sea than the Geysers. Nearly the whole region consists of sulphur, and hot clay, and hot dirty water, and it contains some mountains, called the Sulphur Mountains, from which great quantities The vapour that is always rising from this wretched-looking country, makes a sort of crust over the hot clay; and you will sometimes come to a spot that appears solid, and as you go over it, your horse's hoofs will make holes which will send out steam like little cauldrons. A gentleman who would go over one of these on foot, got terribly scalded by the crust breaking away under him. There is here a sort of hut, from the bottom of which much steam rises, and it is used as a vapour bath. People that are affected with various diseases, come to it from the surrounding country in considerable numbers. At a little distance from this you come to the brink of a cliff, and looking over it, you see twelve large ponds or basins of black mud, boiling, and splashing, and raging perpetually, with large volumes of vapour rolling off their surfaces. Besides these, there is a kind of Geyser of mud, which just resembles the real Geysers in its action; but instead of sending up beautiful clear water, it throws out black unsightly mud, as thick as porridge, which is caught in a nearly round reservoir of more than one hundred feet in diameter. It is situated near the summit of a mountain called Krabla and the reservoir seems to have been in time past a volcanic crater. Of course there cannot be hot water without some source of heat, and there must, therefore, be a source of heat taken into consideration in the action of the Geysers. Now, I do not wish to speak of this here, I only wish to make you understand how it seems likely that the eruptions This cut is intended to represent what may be a section of the subterranean reservoir, S W, of the great Geyser, and the pipe, P, connected with the saucer-shaped basin, B, at the top of the mound. You see the cracks in the rock through which you must suppose hot water constantly trickling into the reservoir. The space S will be constantly full of steam, and the space below, W, will be always full of water. The water will continue to rise till it gets to A, and it will then quite stop up the escape of the steam. The steam in S will then press upon the surface of the water, and force it up the pipe P If you will take the trouble to understand this section, you will see how reasonable it is that the Geyser should be so constructed; and I have seen a little apparatus made of glass, which showed exactly the same sort of operations. Some little variation in the shape of the reservoir and pipe, may perhaps be needed to account for all that takes place; but the principle of the activity being produced by the agency of steam, acting in a space which may be enclosed by the water in its rising to a certain height, seems to be certain and satisfactory. |