New Zealand—Boiling Fountains and Lakes
In the eruptions of mud volcanoes, described in the foregoing chapter, a frequent ingredient is boiling water. There are, however, several instances in which there are thrown up jets of boiling water that are not intermingled with mud, but in which the water is either pure or impregnated with some mineral which it holds in perfect solution. Of this nature are the Geysers of Iceland and California, already described.
In New Zealand there is another variety of this phenomenon, the boiling water issuing forth, not in intermittent jets, as in the Geysers, but in perpetually flowing springs, forming lakes, in which the water remains nearly at the boiling point. These springs and lakes occur at a place called Roto-Mahana. The annexed woodcut will convey an idea of their appearance.
There are several basins raised one above another, and all higher than the level of the large lake. The highest is of an oval form, and about two hundred and fifty feet in circumference. It is filled from an opening at the height of about a hundred feet above the level of the lower lake. At various stages below this upper basin are numerous other springs, from which several similar basins are filled. The whole of these basins empty themselves into the large lake below, and the water in all of them is nearly boiling hot, giving forth, with a hissing sound, volumes of white vapour.
[Illustration: Boiling Lakes of Roto Mahana]
These waters are richly impregnated with carbonate of lime, which has formed all round the margins of the basins beautiful incrustations of snowy whiteness. The sand round the lake is very warm; and if a stick be thrust into it, jets of steam arise.
Doubtless, some years hence, the enterprising English settlers will establish hot baths here. Not far from the lake there are smaller basins, in which the water is not beyond what would be agreeable for a warm bath; while it is of a blue colour and beautifully clear.
On both banks of the river Waikato, also in this neighbourhood, are found numerous basins full of boiling mud or slime, which cannot be approached save with extreme care, owing to the softness and slipperiness of the soil. The largest of these basins is oval in form, 14 feet long by 8 feet wide, and about as much in depth. It contains hot mud of a bright red colour, being strongly impregnated with oxide of iron. Large viscous bubbles are continually rising to the top, and on bursting they emit a fetid, sulphureous smell. These phenomena are nearly akin to those of a mud volcano.
Underground Sounds—Quito—Rio Apure—Guanaxuato—Melida—Nakous.
Not the least remarkable among the phenomena produced by volcanic forces, are the strange underground noises which are occasionally heard. For the most part these are the preludes either of shocks of earthquake or of volcanic eruptions. Those which for months preceded the upheaval of the volcano of Jorullo, will recur to your remembrance. For about a month before the great mud eruption from Tunguragua on 4th February 1797, already described, there proceeded from the interior of that mountain noises of the most fearful kind. These would occur suddenly in the midst of perfect silence. They were heard by Antonio Pineda, the naturalist, who was there at the time, and they led him to foretell the approach of some great convulsion. Strange to say, however, the catastrophe itself was unaccompanied by underground noises any where near the volcano. But, stranger still, at Quito, which is distant about 200 miles, a short time after the eruption began, there were heard tremendous underground thunders. But this distance, between the site of the underground noises and the probable focus of disturbance, was far exceeded in another remarkable instance. It is stated by Humboldt that, in the grassy plains of Calaboso, on the banks of the Rio Apure, a tributary of the Orinoco, there were heard, over a large extent of country, loud underground thunders, unaccompanied by any shaking of the ground; while great streams of lava were being poured forth from the crater of Morne-Garou, in the Island of St. Vincent, at the distance of no less than 632 miles in a right line. This was as though an eruption of Mount Vesuvius were accompanied by underground thunders in Normandy.
There have, nevertheless, been instances of the existence of such underground noises, without their having been followed either by an earthquake, by a volcanic eruption, or any other outward appearance whatever. One of the most remarkable cases of the kind, was that mentioned by Humboldt as having occurred at Guanaxuato in Mexico, a mountain-city situated far from any active volcano. This celebrated traveller states that these noises began on the 9th of January 1784, and lasted above a month. The sounds were at first neither very loud nor very frequent; but from the 15th to the 16th of January they resembled continuous low rolling thunder, alternating with short loud thunder-claps. The sounds then gradually died away and nothing came of them, although they excited great terror among the inhabitants while they lasted. There are mines in the neighbourhood fifteen hundred and ninety-eight English feet in depth, yet neither in them nor at the surface could the least tremor be detected.
A somewhat similar phenomenon occurred in the Island of Melida in the Adriatic, off the coast of Dalmatia, where underground rumblings were heard from March 1822 to September 1824; but in this case the sounds were sometimes accompanied by shocks.
A still more singular phenomenon of this sort occurs on the borders of the Red Sea, at a place called Nakous, where intermittent underground sounds have been heard for an unknown number of centuries. It is situated at about half a mile's distance from the shore, whence a long reach of sand ascends rapidly to a height of about three hundred feet. This reach is about eighty feet wide, and resembles an amphitheatre, being walled in by low rocks. The sounds coming up from the ground at this place recur at intervals of about an hour. They at first resemble a low murmur; but ere long there is heard a loud knocking, somewhat like the strokes of a bell, and which, at the end of about five minutes, becomes so strong as to agitate the sand.
The explanation of this curious phenomenon given by the Arabs, is, that there is a convent under the ground here, and that these sounds are those of the bell, which the monks ring for prayers. So they call it "Nakous," which means a bell. The Arabs affirm that the noise so frightens their camels when they hear it as to render them furious. Philosophers attribute the sounds to suppressed volcanic action—probably to the bubbling of gas or vapours underground.
Extinct Volcanoes—Auvergne—Vienne—Agde—Eyfel—Italy—LacusCimini—Grotto del Cane—Guevo Upas—Talaga Bodas—The Dead Sea.
There are two sorts of extinct volcanoes:first, those in which all evidences of activity have entirely ceased; and,secondly, those in which a subdued state of activity lingers. The former are more widely distributed than the latter; but sometimes both kinds occur in the same district of country.
Extinct volcanoes are found in the district of Auvergne in France. Solidified streams of lava occur at Volvic near Riom; and the crater whence they descended is still visible on the top of the Puy de Nugere. It is an oblong basin, having its edge broken on the side down which the lava flowed. In its descent the fiery stream appears to have encountered a knoll of granite, by which it was divided into two branches. These seem to have reunited lower down, and thence to have overspread the valley beneath.
The Puy de Côme, a mountain near Clermont, appears to have sent forth two streams of lava, which have effected considerable changes in the surface of the country—blocking up the courses of rivers diverting them into new channels, and forming swamps in the old. On the top of Puy Pariou, to the north of Clermont, there exists a perfect crater, quite round, and about two hundred and fifty feet deep, whence there has flowed a stream of lava, whose course can be distinctly traced. The summit of Puy Graveniere, a long round-backed hill also near Clermont, consists almost entirely of a heap of volcanic cinders, which have obliterated all traces of a crater; but two streams of lava appear to have flowed from the sides of the mountain. The Puy de Dôme, and the mountains in its neighbourhood, likewise appear to be of volcanic origin, and to have been upheaved somewhat in the same manner as Jorullo. Although the aspect of the mountains of Auvergne indicates so clearly their having been active since the surrounding country acquired its present general conformation, neither history nor tradition has preserved any record of their eruptions.
There is extant, however, a letter from Sidonius Apollinaris, a cotemporary of Pliny, addressed to the Bishop of Vienne, in which he refers to forms of prayer which had been appointed by the bishop at the time when earthquakes demolished the walls of Vienne, and the mountains, opening, vomited forth torrents of inflamed materials. It hence appears that the extinct volcanoes in the neighbourhood of Vienne, and perhaps those of Le Puy, had been in a state of eruption not long after the beginning of the Christian era. To the westward of the latter town, there is a number of small volcanic craters, of which the two largest are the Lake de Bouchet and the Crater of Bar, which also appears to have been at one time a lake, but is now dry. The former has its greatest diameter about 2300 feet, with a depth of about 90 feet. The latter is on the top of a mountain, which is composed entirely of such substances as are ejected by volcanoes. Its diameter is about 1660, and its depth about 130 feet; while it is almost perfect in its form. The mountains near Vienne exhibit streams of lava, which accommodate themselves to the existing valleys. Near Agde also, on the shores of the Gulf of Lions, on the top of a hill named St. Loup, there is an extinct crater, whence have descended two streams of lava apparently of recent origin. On one of them the town of Agde has been built; the other projects into the sea.
The district of Eyfel, on the borders of the Rhine, is another in which extinct volcanoes abound. They occur mostly in the form of circular craters, which are now filled with water, their borders consisting of volcanic ejections. They also exhibit various superficial streams of lava. One of the most remarkable of these round craters lies near Andernuch, a little west of the Rhine. It is named the Lake of Laach, and is nearly two miles in circumference. On its margin are found numerous volcanic ejections, exactly resembling those of Mount Vesuvius. Notwithstanding these evidences that the extinct volcanoes of Eyfel have been in activity since the country acquired its present conformation, there are no historical records of their operations. There is, indeed, a passage in Tacitus referring to fires that issued from the earth near Cologne; but his description does not warrant the conclusion that the event to which he alludes was of the nature of a volcanic eruption. The Drachenfels on the eastern bank of the Rhine, and the other mountains in its neighbourhood, belong to the more ancient volcanic formations. The same may be affirmed of the other mountains scattered throughout Germany and central Europe generally, in which rocks of volcanic origin occur.
There are a good many traces of extinct volcanoes in Italy, besides those of the Phlegræan fields already mentioned. In general character they resemble those previously described. The chief localities are certain lakes, near Volterra in Tuscany, which give forth very hot sulphurous and boracic acid vapours; a small sulphureous lake near Viterbo continually giving forth bubbles of gas; the Lake of Vico between Viterbo and Rome; the mountain and Lake of Albano near Rome; Mount Vultur in the Apennines, in the province of the Basilicata; and Lake Agnano near Naples. Of these, the Lakes of Vico and Agnano are the most interesting. The former is the ancient Lacus Cimini, and old authors state that its site was once occupied by a town, whose ruins used to be visible at the bottom of the lake when the water was clear. The ground, with the town upon it, is said to have been ingulfed during a volcanic convulsion, when the lake was formed in its place.
The Lake Agnano is the site of an ancient volcanic crater, and on its margin is situated the Grotto del Cane, so famous for the deadly vapours it exhales. These consist of carbonic acid gas, in combination with watery vapour. This celebrated Grotto is thus described, in his work on volcanoes, by Dr. Daubeny, who visited the spot:—
"The mouth of the cavern being somewhat more elevated than its interior, a stratum of carbonic acid goes on constantly accumulating at the bottom, but upon rising above the level of its mouth, flows like so much water over the brim. Hence the upper part of the cavern is free from any noxious vapour; but the air of that below is so fully impregnated, that it proves speedily fatal to any animal that is immersed in it, as is shown to all strangers by the experiment with the dog.
"The sensation I experienced, on stooping my head for a moment to the bottom, resembled that of which we are sometimes sensible on drinking a large glass of soda water in a state of brisk effervescence. The cause in both instances is plainly the same.
"The quantity of carbonic acid present in the cavern at various heights, was shown by immersing in it various combustibles in a state of inflammation. I found that phosphorus would continue lighted at about two feet from the bottom, whilst a sulphur match went out a few inches above, and a wax taper at a still higher level.
"It was impossible to fire a pistol at the bottom of the cavern, for although gunpowder may be exploded even in carbonic acid by the application of a heat sufficient to decompose the nitre, and consequently to envelop the mass in an atmosphere of oxygen gas, yet the mere influence of a spark from steel produces too slight an augmentation of temperature for this purpose."
Similar phenomena, but on a grander scale, are presented by the extinct crater in the Island of Java called "Guevo Upas," the Poison-Valley. It is a level about half a mile in circumference, surrounded by precipitous rocks. From various parts of its soil carbonic acid gas is discharged in such quantities as to prove fatal to any animal venturing nigh. The ground is consequently strown with numerous skeletons. This valley gave rise to the famous figment about the upas-tree, which once obtained such general belief in Europe.
There is another extinct crater in Java, whence are exhaled vapours equally deadly, but which exert a most peculiar effect on the dead carcasses subjected to their influence. Instead of their being, as in the Gruevo Upas, reduced to skeletons, the carcasses have all their bones dissolved by the vapours; while the flesh, skin, hair, and nails are by their action preserved from decay. This remarkable crater is situated near the volcano of Talaga Bodas.
Of all the extinct volcanoes in the world, however, none is so remarkable as the Dead Sea. That singular collection of salt and bitter water has the level of its surface depressed 1312 feet below that of the Mediterranean—thus indicating an enormous subsidence. The Dead Sea occupies the site of what was formerly the plain of Jordan, described as having been "well-watered everywhere, as the garden of the Lord, like the land of Egypt." One part of it, called the Vale of Siddim, was full of slime-pits—the only indications of volcanic action. When the cities of Sodom and Gomorrah, which stood in the plain, were destroyed, the Lord, it is said, rained upon them fire and brimstone from heaven; but while these fell upon the cities from the atmosphere, it appears that they must have primarily been discharged from the earth; for "the smoke of the country went up as the smoke of a furnace." The phenomena, therefore, most likely resembled, in the first instance, those of Jorullo; but the catastrophe seems to have ended like the last great eruption of the volcano in Timor—the whole of the plain having been ingulfed and replaced by the salt lake, whose depressed level so clearly indicates the nature of its origin.