Account of the Eruption of the Volcano of Jorullo in Mexico.

By Baron Alexander de Humboldt.

With a Section of the Mountain.

We have given the above abridged account of this remarkable volcano, in reference to a new theory of its formation by Mr Scrope, which forms the subject of the next Article.

See Humboldt’s Essai Politique sur la Nouvelle Espagne, his Essai Geognostique, p. 351, and his Relation Historique.—Ed.

To the east of the Pic de Tancitaro, the Volcan de Jorullo (Xorullo, or Juruyo) was formed in the night of the 29th September 1759. M.

Bonpland and myself reached its crater on the 19th September 1803.

The great catastrophe in which this mountain rose from the earth, and by which a considerable extent of ground totally changed its appearance, is, perhaps, one of the most extraordinary physical revolutions in the annals of the history of our planet.

Geology gives us no example of the formation, from the centre of a thousand small burning cones, of a mountain of scoria and ashes 517 metres (1695 feet) in height, comparing it only with the level of the old adjoining plains in the interior of a continent, 36 leagues distant from the coast, and more than 42 leagues from every other active volcano.

A vast plain extends from the hills of Aguasarco to near the villages of Teipa and Petatlan, both equally celebrated for their fine plantations of cotton.

This plain, between the Picachos del Mortero, the Cerros de las Cuevas, y de Cuiche, is only from 750 to 800 metres (from 2460 to 2624 feet) above the level of the sea.

In the middle of a tract of ground in which porphyry, with a base of greenstone predominates, basaltic cones appear, the summits of which are crowned with evergreen oaks of a laurel and olive foliage, intermingled with small palm trees with flabelliform leaves.

This beautiful vegetation forms a singular contrast with the aridity of the plain, which was laid waste by volcanic fire.

Till the middle of the 18th century, fields cultivated with sugar-cane and indigo occupied the extent of ground between the two brooks called Cuitamba and San Pedro.

They were bounded by basaltic mountains, of which the structure seems to indicate that all this country, at a very remote period, had been already several times convulsed by volcanoes.

These fields, watered by artificial means, belonged to the plantation (hacienda) of San Pedro de Jorullo, one of the greatest and richest of the country.

In the month of June 1759, a subterraneous noise was heard.

Hollow noises of a most alarming nature (bramidos,) were accompanied by frequent earthquakes, which succeeded one another for from 50 to 60 days, to the great consternation of the inhabitants of the hacienda.

From the beginning of September every thing seemed to announce the complete re-establishment of tranquillity, when, in the night between the 28th and 29th, the horrible subterraneous noise recommenced.

The affrighted Indians fled to the mountains of Aguasarco.

A tract of ground from three to four square miles in extent, which goes by the name of Malpays, rose up in the shape of a bladder.

The bounds of this convulsion are still distinguishable in the fractured strata.

The Malpays near its edges is only 39 feet above the old level of the plain called the playas de Jorullo; but the convexity of the ground thus thrown up increases progressively towards the centre to an elevation of 524 feet.

See Plate I. Fig. 6.

Those who witnessed this great catastrophe from the top of Aguasarco assert that flames were seen to issue forth for an extent of more than half a square league, that fragments of burning rocks were thrown up to prodigious heights, and that, through a thick cloud of ashes, illumined by the volcanic fire, the softened surface of the earth was seen to swell up like an agitated sea.

The rivers of Cuitamba and San Pedro precipitated themselves into the burning chasms.

The decomposition of the water contributed to invigorate the flames, which were distinguishable at the city of Pascuaro, though situated on a very extensive table land 1400 metres (4592 feet) elevated above the plains of las playas de Jorullo.

Eruptions of mud, and especially of strata of clay, enveloping balls of decomposed basaltes in concentrical layers, appear to indicate, that subterraneous water had no small share in producing this extraordinary revolution.

Thousands of small cones, from two to three metres (from 6.5 feet to 9.8 feet) in height, called by the indigenes ovens (hornitos,) issued forth from the Malpays.

Although within the last fifteen years, according to the testimony of the Indians, the heat of these volcanic ovens has suffered a great diminution, I have seen the thermometer rise to 95° (202° of Fahrenheit) on being plunged into fissures which exhale an aqueous vapour.

Each small cone is a fumarola, from which a thick vapour ascends to the height of ten or fifteen metres.

In many of them a subterraneous noise is heard, which appears to announce the proximity of a fluid in ebullition.

In the midst of the ovens six large masses, elevated from 4 to 500 metres (from 312 to 1640 feet) each above the old level of the plains, sprung up from a chasm, of which the direction is from the N.N.E. to the S.S.E. This is the phenomenon of the Montenovo of Naples, several times repeated in a range of volcanic hills.

The most elevated of these enormous masses, which bears some resemblance to the pays de l’Auvergne, is the great Volcan de Jorullo. It is continually burning, and has thrown up from the north side an immense quantity of scorified and basaltic lavas, containing fragments of primitive rocks.

These great eruptions of the central volcano continued till the month of 1760.

In the following years they became gradually less frequent.

The Indians, frightened at the horrible noises of the new volcano, abandoned, at first, all the villages situated within seven or eight leagues distance of the playas de Jorullo.

They became gradually, however, accustomed to this terrific spectacle; and, having returned to their cottages, they advanced towards the mountains Aguasarco and Santa In̄es, to admire the streams of fire discharged from an infinity of great and small volcanic apertures.

The roofs of the houses of Queretaro were then covered with ashes at a distance of more than 48 leagues in a straight line from the scene of the explosion.

Although the subterraneous fire now appears far from violent, and the Malpays, and the great volcano, begin to be covered with vegetables, we, nevertheless, found the ambient air heated to such a degree by the action of the small ovens (hornitos,) that the thermometer, at a great distance from the surface, and in the shade, rose as high as 48° (109° of Fahrenheit.)

This fact appears to prove, that there is no exaggeration in the accounts of several old Indians, who affirm that, for many years after the first eruption, the plains of Jorullo, even at a great distance from the scene of the explosion, were uninhabitable, from the excessive heat which prevailed in them.

We found, in the bottom of the crater, the air at 116°, 130°, and 139° of Fahrenheit.

We passed over crevices which exhaled a sulphureous vapour, in which the thermometer rose to 185° Fahrenheit.

The passage over these crevices and heaps of scoria, which cover considerable hollows, render the descent into the crater very dangerous.

The traveller is still shown, near the Cerro de Santa In̄es, the rivers of Cuitamba and San Pedro, of which the limpid waters formerly watered the sugar-cane plantation of Don André Pimentel.

These streams disappeared in the night of the 29th September 1759; but, at a distance of 2000 metres (6561 feet) farther west, in the tract which was the theatre of the convulsion, two rivers are now seen bursting through the argillaceous vault of the hornitos, of the appearance of mineral waters, in which the thermometer rises to 52°,7 (126°,8 of Fahrenheit.)

The Indians continue to give them the names of San Pedro and Cuitamba, because, in several parts of the Malpays, great masses of water are heard to run in the direction from east to west, from the mountains of Santa In̄es towards l’Hacienda de la Presentacion.

Near this habitation there is a brook, which disengages itself from the sulphureous hydrogen.

It is more than nine yards in breadth, and is the most abundant hydro-sulphureous spring which I have ever seen.

The position of the new Volcana de Jorullo gives rise to a very curious geological observation.

In New Spain there is a parallel of great elevations, or a narrow zone contained between 18°, 59′ and 19°, 12′ of latitude, in which all the summits of Anahuac which rise above the region of perpetual snow are situated.

These summits are either volcanoes which still continue to burn, or mountains which, from their form, as well as the nature of their rocks, have, in all probability, formerly contained subterraneous fire.

As we recede from the coast of the Atlantic, we find, in a direction from east to west, the Pic d’Orizaba, the two volcanoes of la Puebla, the Nevada de Toluca, the Pic de Tancitaro, and the Volcan de Colima.

These great elevations, in place of forming the crest of the Cordillera of Anahuac, and following its direction, which is from the south-east to the north-west, are, on the contrary, placed on a line perpendicular to the axis of the great chain of mountains.

It is undoubtedly worthy of observation, that, in 1759, the new volcano of Jorullo was formed in the prolongation of that line, on the same parallel with the ancient Mexican volcanoes!

A single glance bestowed on my plan of the environs of Jorullo will prove that the six large masses rose out of the earth, in a line which runs through the plain from the Cerro de las Cuevas to the Picacho del Mortero; and it is thus also that the bocche nove of Vesuvius are ranged along the prolongation of a chasm.

Do not these analogies entitle us to suppose that there exists, in this part of Mexico, at a great depth in the interior of the earth, a chasm in a direction from east to west, for a length of 137 leagues, along which the volcanic fire, bursting through the interior crust of the porphyritical rocks, has made its appearance at different epochas from the gulf of Mexico to the South Sea?

Does this chasm extend to the small group of islands called by M. Collnet the archipelago of Revillagigedo, around which, in the same parallel with the Mexican volcanoes, pumice-stone has been seen floating?

Those naturalists who make a distinction between the facts which are offered us by descriptive geology and theoretical reveries on the primitive state of our planet, will forgive us these general observations on the general map of New Spain.

Moreover, from the lake of Cuiseo, which is impregnated with muriate of soda, and which exhales sulphuretted hydrogen, as far as the city of Valladolid, for an extent of 48 square leagues, there are a great quantity of hot wells, which generally contain only muriatic acid, without any vestiges of terreous sulphates or metallic salts.

Such are the mineral waters of the Chucandiro, Cuinche, San Sebastian, and San Juan Tarraramco.

Abbildungen