Cosmos, Vol. 1 · Alexander von Humboldt
*[The little island of Volcano is separated from Lipari by a narrow channel. It appears to have exhibited strong signs of volcanic activity long before the Christian era, and still emits gaseous exhalations. Stromeyer detected the presence of selenium in a mixture of sal ammoniac and sulphur. Another product, supposed to be peculiar to this volcano, is boracic acid, which lines the sides of the cavities in beautiful white silky crystals. Daubeney, op. cit., p. 257.] -- Tr.
The vapors that rise from the 'fumarolles' cause the sublimation of the chlorids of iron, copper, lead, and ammonium; iron glanceI and chlorid of sodium (the latter often in large quantities) fill the cavities of recent lava streams and the fissures of the margin of the crater.
*Regarding the chemical origin of iron glance in volcanic masses, see Mitscherlich, in Poggend., 'Annalen', bd. xv., s. 630; and on the liberation of hydrochloric acid in the crater, see Gay-Lussac, in the 'Annals de Chimique et de Physique', t. xxii., p. 423.
The mineral composition of lava differs according to the nature of the crystalline rock of which the volcano is formed, the height of the point where the eruption occurs, whether at the foot of the mountain or in the neighborhood of the crater, and the condition of temperature of the interior. Vitreous volcanic formations, obsidian, pearl-stone, and pumice, are entirely wanting in some volcanoes, while in the case of others they only proceed from the crater, or, at any rate, from very considerable heights. These important and involved relations can only be explained by very accurate crystallographic and chemical investigations. My fellow-traveler in Siberia, Gustav Rose, and subsequently Hermann Abich, have already been able, by their fortunate and ingenious researches, to throw much light on the structural relations of the various kinds of volcanic rocks.
The greater part of the ascending vapor is mere steam. When condensed, this forms springs, as in Pantellaria,Iwhere they are used by the goatherds of the island.
*[Steam issues from many parts of this insular mountain, and several hot springs gush forth from it, which form together a lake 6000 feet in circumference. Daubeney, op. cit.] -- Tr.
On the morning of the 26th of October, 1822, a current was seen to flow from a lateral fissure of the crater of Vesuvius, and was loong supposed to have been boiling water; it was, however, shown, by Monticelli's accurate investigations, to consist of dry ashes, which fell like sand, and of lava pulverized by friction. The ashes, which sometimes darken the air for hours and days together, and produce great injury to the vineyards and olive groves by adhering to the leaves, indicate by their columnar ascent, impelled by vapors, the termination of every great eqrthquake. This is the magnificent phenomenon which Pliny the younger, in his celebrated letter to Cornelius Tacitus, compares, in the case of Vesuvius, to the form of a lofty and thickly-branched and foliaceous pine. That which is described as flames in the eruption of scoriae, and the radiance of the glowing red clouds that hover over the crater, can not be ascribed to the effect of hydrogen gas in a state of combustion. They are rather reflections of light which issue from molten masses, projected high in the air, and also reflections from the burning depths, whence the glowing vapors ascend. We will not, however, attempt to decide the nature of the flames, which are occasionally seen now, as in the time of Strabo, to rise from the deep sea during the activity of littoral volcanoes, or shortly before the elevation of a volcanic island.
When the questions are asked, what is it that burns in the volcano? what excites the heat, fuses together earths and metals, and imparts to lava currents of thick layers a degree of heat that lasts for many years? it is necessarily implied that volcanoes must be connected with the existence of substances capable of maintaining combustion, like the beds of coal in subterranean fires.
*See the beautiful experiments on the cooling of masses of rock, in Bischof's 'Warmelehre', s. 384, 443, 500-512.
According to the different phases of chemical science, bitumen, pyrites, the moist admixture of finely-pulverized sulphur and iron, pyrophoric substances, and the metals of the alkalies and earths, have in turn been designated as the cause of intensely active volcanic phenomena. The great chemist, Sir Humphrey Davy, to whom we are indebted for the knowledge of the most combustible metallic substances, has himself renounced his bold chemical hypothesis in his last work ('Consolation in Travel, and last Days of a Philosopher') -- a work which can not fail to excite in the reader a feeling of the deepest melancholy. the great mean density of the earth (5.44), when compared with the specific weight of potassium (0.865), of sodium (-.972), or of the metals of the earths (1.2), and the absence of hydrogen gas in the gaseous emanations from the fissures of craters, and from still warm streams of lava, besides many chemical considerations, stand in opposition with the earlier conjectures of Davy and Ampere.*
*See Berzelius and Wohler, in Poggend., 'Annalen', bd. i., s. 221, and bd. xi., s. 146; Gay-Lussac, in the 'Annals de Chimie', t. x., xii., p. 422; and Bischof's 'Reasons against the Chemical Theory of Volcanoes', in the English edition of his 'Warmelehre', p. 297-309.
If hydrogen were evolved from erupted lava, how great must be the quantity of the gas disengaged, when, the seat of the volcanic activity being very low, as in the case of the remarkable eruption at the foot of the Skaptar Jokul in Iceland (from the 11th of June to the 3d of August, 1783, described by Mackenzie and Soemund Magnussen), a space of many square miles was covered by streams of lava, accumulated to the thickness of several hundred feet! Similar difficulties are opposed to the assumption of the penetration of the atmospheric air into the crater, or, as it is figuratively expressed, the 'inhalation of the earth', when we have regard to the small quantity of nitrogen emitted. So general, deep-seated, and far-propagated an activity as that of volcanoes, can not assuredly have its source in chemical affinity, or in the mere contact of individual or merely locally distributed substances. Modern geognosy* rather seeks the cause of this activity in the increased temperature with the increase of depth at all degrees of latitude, in that powerful internal heat which our planet owes to its first solidification, its formation in the regions of space, and to the spherical contraction of matter revolving elliptically in a gaseous condition.
*[On the various theories that have been advanced in explanation of volcanic action, see Daubeney 'On Volcanoes', a work to which we have made continual reference during the preceding pages, as it constitutes the most recent and perfect compendium of all the important facts relating to this subject, and is peculiarly adapted to serve as a source of reference to the 'Cosmos', since the learned author in many instances enters into a full exposition of the views advanced by Baron Humboldt. The appendix contains several valuable notes with reference to the most recent works that have appeared on the Continent, on subjects relating to volcanoes; among others, an interesting notice of Professor Bischof's views "on the origin of the carbonic acid discharged from volcanoes," as enounced in his recently published work, 'Lehrbuch der Chemischen und Physikalischen Geologie'.] -- Tr.
We have thus mere conjecture and supposition side by side with certain knowledge. A philosophical study of nature strives ever to elevate itself above the narrow requirements of mere natural description, and does not consist, as we have already remarked, in the mere accumulation of isolated facts. The inquiring and active spirit of man must be suffered to pass from the present to the past, to conjecture all that can not yet be known with certainty, and still to dwell with pleasure on the ancient myths of geognosy which are presented to us under so many various forms. If we consider volcanoes as irregular intermittent springs, emitting a fluid mixture of oxydized metals, alkalies, and earths, flowing gently and calmy wherever then find a passage, or being upheaved by the powerful expansive force of vapors, we are involuntarily led to remember the geognostic visions of Plato, according to which hot springs, as well as all volcanic igneous streams, were eruptions that might be traced back to one generally distributed subterranean cause, 'Pyriphlegethon'.*
*According to Plato's geognostic views, as developed in the 'Phaedo', Pyriphlegethon plays much the same part in relation to the activity of volcanoes that we now ascribe to the augmentation of heat as we descend from the earth's surface, and to the fused condition of its internal strata. ('Phaedo', ed. Ast, p. 603 and 607; Annot., p. 308 and 817.) "Within the earth, and all around it, are larger and smaller caverns. Water flows there in abundance; also much fire and large streams of fire, and streams of moist mud (some purer and others more filthy), like those in Sicily, consisting of mud and fire, preceding the great eruption. These streams fill all places that fall in the way of their course. Pyriphlegethon flows forth into an extensive district burning with a fierce fire, where it forms a lake larger than our sea, boiling with water and mud. From thence it moves in circles round the earth, turbid and muddy." This stream of molten earth and mud is so much the general cause of volcanic phenomena, that Plato expressly adds, "thus is Pyriphlegethon constituted, from which also the streams of fire ([Greek words]), wherever they reach the earth ([Greek words]), inflate such parts (detached fragments)." Volcanic scoriae and lava streams are therefore portions of Pyriphlegethon itself, portions of the subterranean molten and ever-undulating mass. That {Greek words] are lava streams, and not, as Schneider, Passow, and Schleiermacher will have it, "fire-vomiting mountains," is clear enough from many passages, some of which have been collected by Ukert ('Geogr. der Griechen und Romer', th. ii., s. 200): [Greek word] is the volcanic phenomenon in reference to its most striking characteristic, the lava stream. Hence the expression, the [Greek word] of Aetna. Aristot. 'Mirab. Ausc.', t. ii., p. 833; sect. 38, Bekker; Thucyd., iii., 116; Theophrast., 'De Lap'., 22, p. 427, Schneider; Diod., v., 6, and xiv., 59, where are the remarkable words, "Many places near the sea, in the neighborhood of Aetna, were leveled to the ground, [Greek words];" Strabo, vi., p. 269; xiii., p. 268, and where there is a notice of the celebrated burning mud of the Lelantine plains, in Euboea, i., p. 58, Casaub.; and Appian, 'De Bello Civili', v., 114. The blame which Aristotle throws on the geognostical fantasies of the Phaedo ('Meteor.', ii., 2, 19) is especially applied to the sources of the rivers flowing over the earth's surface. The distinct statement of Plato, that "in Sicily eruptions of wet mud precede the glowing (lava) stream," is very remarkable. Observations on Aetna could not have led to such a statement, unless pumice and ashes, formed into a mud-like mass by admixture with melted snow and water, during the volcano-electric storm in the crater of eruption, were mistaken for ejected mud. It is more probable that Plato's streams of moist mud ([Greek words]) originated in a faint recollection of the salses (mud volcanoes) of Agrigentum, which, as I have already mentioned, eject argillaceous mud with a loud noise. It is much to be regretted, in reference to this subject, that the work of Theophrastus [Greek words] 'On the Volcanic Stream in Sicily', to which Diog. Laert., v., 49, refers, has not come down to us.
The different volcanoes over the earth's surface, when they are considered independently of all climatic differences, are acutely and characteristically classified as central and linear volcanoes. Under the first name are comprised those which constitute the central point of many active mouths of eruption, distributed almost regularly in all directions; under the second, those lying at some little distance from one another, forming, as it were, chimneys or vents along an extended fissure. Linear volcanoes again admit of further subdivision, namely, those which rise like separate conical islands from the bottom of the sea, being generally parallel with a chain of primitive mountains, whose foot they appear to indicate, and those volcanic chains which are elevated on the highest ridges of these mountain chains, of which they form the summits.*
*Leopold von Buch, 'Physikal. Beschreib. der Canarischen Inseln', s. 326-407. I doubt if we can agree with the ingenious Charles Darwin ('Geological Observations on Volcanic Islands', 1844, p. 127) in regarding central volcanoes in general as volcanic chains of small extent on parallel fissures. Friedrich Hoffman believes that in the group of the Lipari Islands, which he has so admirably described, and in which two eruption fissures intersect near Panaria, he has found an intermediate link between the two principal modes in which volcanoes appear, namely, the central volcanoes and volcanic chains of Von Buch (Poggendorf, 'Annalen der Physik', bd. xxvi., s. 81-88).
The Peak of Teneriffe, for instance, is a central volcano, being the central point of the volcanic group to which the eruption of Palma and Landerote may be referred. The long, rampart-like chain of the Andes, which is sometimes single, and sometimes divided into two or three parallel branches, connected by various transverse ridges, presents, from the south of Chili to the northwest coast of America, one of the grandest instances of a continental volcanic chain. The proxiimity of active volcanoes is always manifested in the chain of the Andes by the appearance of certain rocks (as dolerite, melaphyre, trachyte, andesite, and dioritic porphyry), which divide the so-called primitive rocks, the transition slates and sandstones, and the stratified formations. the constant recurrence of this phenomenon convinced me long since that these sporadic rocks were the seat of volcanic phenomena, and were connected with volcanic eruptions. At the foot of the grand Tunguragua, near Penipe, on the banks of the Rio Puela, I first distinctly observed mica slate resting on granite, broken through by a volcanic rock.
In the volcanic chain of the New Continent, the separate volcanoes are occasionally, when near together in mutual dependence upon one another; and it is even seen that the volcanic activity for centuries together has moved on in one and the same direction, as for instance, from north to south in the province of Quito.*
(Humboldt, 'Geognost. Beobach, uber die Vulkane des Hochlandes von Quito', in Poggend., 'Annal. der Physik', bd. xliv., s. 194.
The focus of the volcanic action lies below the whole of the highlands of this province; the only channels of communication with the atmosphere are, however, those mountains which we designate by special names, as the mountains of Pichincha, Cotopaxi, and Tunguragua, and which, from their grouping, elevation, and form, constitute the grandest and most picturesque spectacle to be found in any volcanic district of an equally limited extent. Experience shows us, in many instances, that the extremities of such groups of volcanic chains are connected together by subterranean communications; and this fact reminds us of the ancient and true expression made use of by Seneca,* that the igneous mountain is only the issue of the more deeply-seated volcanic forces.
*Seneca, while he speaks very clearly regarding the problematical sinking of Aetna, says in his 79th letter, "Though this might happen, not because the mountain's height is lowered, but because the fires are weakened, and do not blaze out with their former vehemence; and for which reason it is that such vast clouds of smoke are not seen in the day-time. Yet neither of these seem incredible, for the mountain may possibly be consumed by being daily devoured, and the fire not be so large as formerly, since it is not self-generated here, but is kindled in the distant bowels of the earth, and there rages, being fed with continual fuel, not with that of the mountain, through which it only makes its passage." The subterranean communication, "by galleries," between the volcanoes of Sicily, Lipari, Pithecusa (Ischia), and Vesuvius, "of the last of which we may conjecture that it formerly burned and presented a fiery circle," seems fully understood by Strabl (lib. i., p. 247 and 248). He terms the whole district "sub-igneous."
In the Mexican highlands a mutual dependence is also observed to exist among the volcanic mountains Orizaba, Popocatepel, Jorullo, and Colima; and I have shown* that they all lie in one direction between 18 degrees 59' and 19 degrees 12' north latitude, and are situated in a transverse fissure running from sea to sea.
*Humboldt, 'Essai Politique sur la Nouv. Espagne', t. ii., p. 173-175.
The volcano of Jorullo broke forth on the 29th of September, 1759, exactly in this direction, and over the same transverse fissure, being elevated to a height of 1604 feet above the level of the surrounding plain. The mountain only once emitted an eruption of lava, in the same manner as is recorded of Mount Epomeo in Ischia, in the year 1302. But although Jorullo, which is eighty miles from any active volcano, is in the strict sense of the word a new mountain, it must not be compared with Monte Nuovo, near Puzzuolo, which first appeared on the 19th of September, 1538, and is rather to be classed among craters of elevation. I believe that I have furnished a more natural explanation of the eruption of the Mexican volcano, in comparing its appearance to the elevation of the Hill of Methone, now Methana, in the peninsula of Troezene. The description given by Strabo and Pausanias of this elevation, led one of the Roman poets, most celebrated for his richness of fancy, to develop views which agree in a remarkable manner with the theory of modern geognosy. "Near Troezene is a tumulus, steep and devoid of trees, once a plain, now a mountain. The vapors inclosed in dark caverns in vain seek a passage by which they may escape. The heavier earth, inflated by the force of the compressed vapors, expands like a bladder filled with air, or like a goat-skin. The ground has remained thus inflated, and the high projecting eminence has been solidified by time into a naked rock." Thus picturesquely, and, as analogous phenomena justify us in believing, thus truly has Ovid described that great natural phenomenon which occurred 282 years before our era, and consequently, 45 years bfore the volcanic separation of Thera (Santorino) and Therasia, between Troezene and Epidaurus, on the same spot where Russegger has found veins of trachyte.*
*Ovid's description of the eruption of Methone ('Metam.', xv., p. 226-306): "Near Troezene stands a hill, exposed in air To winter winds, of leafy shadows bare: This once was level ground; but (strange to tell) Th' included vapors, that in caverns dwell, Laboring with colic pangs, and close confined, In vain sought issue for the rumbling wind: Yet still they heaved for vent, and heaving still, Enlarged the concave and shot up the hill, As breath extends a bladder, or the skins Of goats are blown t'inclose the hoarded wines; The mountain yet retains a mountain's face, And gathered rubbish heads the hollow space." 'Dryden's Translation'. [footnote continues] This description of a dome-shaped elevation on the continent is of great importance in a geognostical point of view, and coincides to a remarkable degree with Aristotle's account ('Meteor.', ii., 89, 17-19) of the upheaval of islands of eruption: "The heaving of the earth does not cease till the wind [(Greek word)] which occasions the shocks has made its escape into the crust of the earth. It is not long ago since this actually happened at Heraclea in Pontus, and a similar event formerly occurred at Hiera, one of the Aeolian Islands. A portion of the earth swelled up, and with loud noise rose into the form of a hill, till the mighty urging blast [(Greek word)] found an outlet, and ejected sparks and ashes which covered the neighborhood of Lipari, and even extended to several Italian cities." In this description, the vesicular distension of the earth's crust (a stage at which many trachytic mountains have remained) is very well distinguished from the eruption itself. Strabo, lib. i., p. 59 (Casaubon), likewise describes the phenomenon as it occurred at Methone: near the town, in the Bay of Hermione, there arose a flaming eruption; a fiery mountain, seven (?) stadia in height, was then thrown up, which during the day was inaccessible from its heat and sulphureous stench, but at night evolved an agreeable odor (?) , and was so hot that the sea boiled for a distance of five stadia, and was turbid for full twenty stadia, and also was filled with detached masses of rock. Regarding the present mineralogical character of the peninsula of Methana, see Fiedler, 'Reise durch Griechenland', th. i., s. 257-263.
Santorino is the most important of all the 'islands of eruption' belonging to volcanic chains.*
*[I am indebted to the kindness of Professor E. Forbes for the following interesting account of the island of Santorino, and the adjacent islands of Neokaimeni and Microkaimeni. "The aspect of the bay is that of a great crater filled with water, Thera and Therasia forming its walls, and the other islands being after-productions in its center. We sounded with 250 fathoms of line in the middle of the bay, between Therasia and the main islands, but got no bottom. Both these islands appear to be similarly formed of successive strata of volcanic ashes, which, being of the most vivid and variegated colors, present a striking contrast to the black and cindery aspect of the central isles. Neokaimeni, the last-formed island, is a great heap of obsidian and scoriae. So, also, is the greater mass, Microkaimeni, which rises up in a conical form, and has a cavity or crater. On one side of this island, however, a section is exposed, and cliffs of fine pumiceous ash appear stratified in the greater islands. In the main island, the volcanic strata abut against the limestone mass of Mount St. Elias in such a way as to lead to the inference that they were deposited in a sea bottom in which the present mountain rose as a submarine mass of rock. The people at Santorino assured us that subterranean noises are not unfrequently heard, especially during calms and south winds, when they say the water of parts of the bay becomes the color of sulphur. My own impression is, that this group of islands, constitutes a crater of elevation, of which the outer ones are the remains of the walls, while the central group are of later origin, and consist partly of upheaved sea bottoms and partly of erupted matter -- erupted, however, beneath the surface of the water."] -- Tr.
It combines within itself the history of all islands of elevation. For upward of 2000 years, as far as history and tradition certify, it would appear as if nature were striving to form a volcano in the midst of the crater of elevation."*
*Leop. von Buch, 'Physik. Beschr. der Canar. Inseln', s. 356-358, and particularly the French translation of this excellent work, p. 402; and his memoir in Poggendorf's 'Annalen', bd. xxxviii., s. 183. A submarine island has quite recently made its appearance within the crater of Santorino. In 1810 it was still fifteen fathoms below the surface of the sea, but in 1830 it had risen to within three or four. It rises steeply like a great cone, from the bottom of the sea, and the continuous activity of the submarine crater is obvious from the circumstance that sulphurous acid vapors are mixed with the sea water, in the eastern bay of Neokaimeni, in the same manner as at Vromolimni, near Methana. Coppered ships lie at anchor in the bay in order to get their bottoms cleaned and polished by this natural (volcanic) process. (Virlet, in the 'Bulletin de la Societe Geologique de France', t. iii., p. 109, and Fiedler 'Reise durch Griechenland', th. ii., s. 469 and 584.)
Similar insular elevations, and almost always at regular intervals of 80 or 90 years,* have been manifested in the island of St. Michael, in the Azores; but in this case the bottom of the sea has not been elevated at exactly the same parts.**
*Appearance of a new island near St. Miguel, one of the Azores, 11th of June, 1638, 31st of December, 1719, 13th of June, 1811.
**[My esteemed friend, Dr. Webster, professor of Chemistry and Mineralogy at Harvard College, Cambridge, Massachusetts, U. S., in his 'Description of the Island of St. Michael, etc.', Boston, 1822, gives an interesting account of the sudden appearance of the island named Sabrina which was about a mile in circumference, and two or three hundred feet above the level of the ocean. After continuing for some weeks, it sank into the sea. Dr. Webster describes the whole of the island of St. Michael as volcanic, and containing a number of conical hills of trachyte, several of which have craters, and appear at some former time to have been the openings of volcanoes. The hot springs which abound in the island are impregnated with sulphureted hydrogen and carbonic acid gases, appearing to attest the existence of volcanic action.] -- Tr.
The island which Captain Tillard named 'Sabrina', appeared unfortunately at a time (the 30th of January, 1811) when the political relations of the maritime nations of Western Europe prevented that attention being bestowed upon the subject by scientific institutions which was afterward directed to the sudden appearance (the 2d of July, 1831), and the speedy destruction of the igneous island of Ferdinandea in the Sicilian Sea, between the limestone shores of Sciacca and the purely volcanic island of Pantellaria.*
*Prevost, in the Bulletin de la Societe Geologique, t. iii., p. 34; Friedrich Hoffman, 'Hinterlassene Werke.' bd. ii., s. 451-456.
The geographical distribution of the volcanoes which have been in a state of activity during historical times, the great number of insular and littoral volcanic mountains, and the occasional, although ephemeral, eruptions in the bottom of the sea, early led to the belief that volcanic activity was connected with the neighborhood of the sea, and was dependent upon it for its continuance. "For many hundred years," says Justinian, or rather Trogus Pompeius, whom he follows,* "Aetna and the Aeolian Islands have been burning, and how could this have continued so long if the fire had not been fed by the neighboring sea?"**
*"Accedunt vicini et perpetui Aetnae montis ignes et insularum Aeolidum, veluti ipsis undis alatur incendium; neque enim aliter durare tot seculis tantus ignis potuisset, nisi humoris nutrimentis aleretur." (Justin, 'Hist. Philipp.', iv., i.) The volcanic theory with which the physical description of Sicily here begins is extremely intricate. Deep fissured; violent motion of the waves of the sea, which, as they strike together, draw down the air (the wind) for the maintenance of the fire: such are the elements of the theory of Trogus. Since he seems from Pliny (xi., 52) to have been a physiognomist, we may presume that his numerous lost works were not confined to history alone. The opinion that air is forced into the interior of the earth, there to act on the vocanic furnaces, was connected by the ancients with the supposed influence of winds from different quarters on the intensity of the fires burning in tna, Hiera, and Stromboli. (See the remarkable passage in Strabo, liv. vi., Aetna.) The mountain island of Stromboli (Strongyle) was regarded therefore, as the dwelling-place of Aeolus, "the regulator of the winds," in consequence of the sailors foretelling the weather from the activity of the volcanic eruptions of this island. The connection between the eruption of a small volcano with the state of the barometer and the direction of the wind is still generally recognized (Leop. von Buch, 'Descr. Phys. des Iles Canaries', p. 334; Hoffmann, in Poggend., 'Annalen', bd. xxvi., s. viii), although our present knowledge of volcanic phenomena, and the slight changes of atmospheric pressure accompanying our winds, do not enable us to offer any satisfactory explanation of the fact. Bembo, who during his youth was brought up in Sicily by Greek refugees, gave an agreeable narrative of his wanderings, and in his 'Aetna Dialogus' (written in the middle of the sixteenth century) advances the theory of the penetration of sea water to the very center of the volcanic action, and of the necessity of the proximity of the sea to active volcanoes. In ascending Aetna the following question was proposed: "Explaina potius nobis quae petimus, ea incendia unde oriantur et orta quomodo perdurent. In omni tellure nuspiam majores fistulae aut meatus ampliores sunt quam in locis, quae vel mari vicina sunt, vel a mari protinus alluntur: mare erodit illa facillime pergitque in viscera terrae. Itaque cum in aliena regna sibi viam faciat, ventis etiam facit; ex quo fit, ut loca quaeque maritima maxime terrae motibus subjecta sint, parum mediterranea. Habes quum in sulfuris venas venti furentes inciderint, unde incendia oriantur tn tuae. Vides, quae mare in radicibus habeat, quae sulfurea sit, quae cavernosa, quae a mari aliquando perforata ventos admiscrit Aestuantes, per quos idonea flammae materies incenderetur."
**[Although extinct volcanoes seem by no means confined to the neighborhood of the present seas, being often scattered over the most inland portions of our existing continents, yet it will appear that, at the time at which they were in an active state, the greater part were in the neighborhood either of the sea, or of the extensive salt or fresh water lakes, which existed at that period over much of what is now dry land. This may be seen either by referring to Dr. Boue's map of Europe, or to that published by Mr. Lyell in the recent edition of his 'Principles of Geology' (1847), from both of which it will become apparent that, at a comparatively recent epoch, those parts of France, of Germany, of Hungary, and of Italy, which afford evidences of volcanic action now extinct, were covered by the ocean. Daubeney 'On Volcanoes', p. 605.] -- Tr.
In order to explain the necessity of the vicinity of the sea, recourse has been had, even in modern times, to the hypothesis of the penetration of sea water into the foci of volcanic agency, that is to say, into deep-seated terrestrial strata. When I collect together all the facts that may be derived from my own observation and the laborious researches of others, it appears to me that every thing in this great quantity of aqueous vapors, which are unquestionably exhaled from volcanoes even when in a state of rest, be derived from sea water impregnated with salt, or rather, perhaps with fresh meteoric water; or whether the expansive force of the vapors (which, at a depth of nearly 94,000 feet, is equal to 2800 atmospheres) would be able at different depths to counterbalance the hydrostatic pressure of the sea, and thus afford them, under certain conditions, a free access to the focus;* or whether the formation of metallic chlorids, the presence of chlorid of sodium in the fissures of the crater, and the frequent mixture of hydrochloric acid with the aqueous vapors, necessarily imply access of sea water; or, finally, whether the repose of volcanoes (either when temporary, or permanent and complete) depends upon the closure of the channels by which the sea or meteoric water was conveyed, or whether the absence of flames and of exhalations of hydrogen (and sulphureted hydrogen gas seems more characteristic of solfataras than of active volcanoes) is not directly at variance with the hypothesis of the decomposition of great masses of water?**
* Compare Gay-Lussac, 'Sur les Volcans', in the 'Annales de Chimie', t. xxii., p. 427, and Bischof, 'Warmelehre', s. 272. The eruptions of smoke and steam which have at different periods been seen in Lancerote, Iceland, and the Kurile Islands, during the eruption of the neighboring volcanoes, afford indications of the reaction of volcanic foci through tense columns of water; that is to say, these phenomena occur when the expansive force of the vapor exceeds the hydrostatic pressure.
** [See Daubeney 'On Volcanoes', Part iii., ch. xxxvi., xxxviii., xxxix.] -- Tr.
The discussion of these important physical questions does not come within the scope of a work of this nature; but, while we are considering these phenomena, we would enter somewhat more into the question of the geographical distribution of still active volcanoes. We find, for instance, that in the New World, three, viz., Jorullo, Popocatepetl, and the volcano of De la Fragua, are situated at the respective distances of 80, 132, and 196 miles from the sea-coast, while in Central Asia, as Abel Remusat* first made known to geognosists, the Thianschan (Celestial Mountains), in which are situated the lava-emitting mountain of Pe-schan, the solfatara of Urumtsi, and the still active igneous mountain (Ho-tscheu) of Turfan, lie at an almost equal distance (1480 to 1528 miles) from the shores of the Polar Sea and those of the Indian Ocean.
*Abel Remusat, 'Lettre a M. Cordier', in the 'Annales de Chimie', t. v., p. 137.
Pe-schan is also fully 1360 miles distant from the Caspian Sea,* and 172 and 218 miles from the seas of Issikul and Balkasch.
*Humboldt, 'Asie Centrale', t. ii., p. 30-33, 38-52, 70-80, and 426-428. The existence of active volcanoes in Kordofan, 540 miles from the Red Sea, has been recently contradicted by Ruppell, 'Reisen in Nubien', 1829, s. 151.
It is a fact worthy of notice, that among the four great parallel mountain chains which traverse the Asiatic continent from east to west, the Altai, the Thianschan, the Kuen-lun, and the Himalaya, it is not the latter chain, which is nearest to Kuen-lun, at the distance of 1600 and 720 miles from the sea, which have fire-emitting mountains like Aetna and Vesuvius, and generate ammonia like the volcano of Guatimala. Chinese writers undoubtedly speak of lava streams when they describe the emissions of smoke and flame, which, issuing from Pe-schan, devastated a space measuring ten li* in the first and seventh centuries of our era.
*[A 'li' is a Chinese measurement, equal to about one thirtieth of a mile.] -- Tr.
Burning masses of stone flowed, according to their description "like thin melted fat." The facts that have been enumerated, and to which sufficient attention has not been bestowed, render it probable that the vicinity of the sea, and the penetration of sea water to the foci of volcanoes, are not absolutely necessary to the eruption of subterranean fire, and that littoral situations only favor the eruption by forming the margin of a deep sea basin, which, covered by strata of water, and lying many thousand feet lower than the interior continent, can offer but an inconsiderable degree of resistance.
The present active volcanoes, which communicate by permanent craters simultaneously with the interior of the earth and with the atmosphere, must have been formed at a subsequent period, when the upper chalk strta and all the tertiary formations were already present: this is shown to be the fact by the trachytic and basaltic eruptions which frequently form the walls of the crater of elevation. Melaphyres extend to the middle tertiary formations, but are found already in the Jura limestone, where they break through the variegated sandstone.*
*Dufrenoy et Elie de Beaumont, 'Explication de la Carte Geologique de la France', t. i., p. 89.
We must not confound the earlier outpourings of granite, quartzose porphyry, and euphotide from temporary fissures in the old transition rocks with the present active volcanic craters.
The extinction of volcanic activity is either only partial -- in which case the subterranean fire seeks another passage of escape in the same mountain chain -- or it is total, as in Auvergne. More recent examples are recorded in historical times, of the total extinction of the volcano of Mosychlos,* on the island sacred to Hephaestos (Vulcan), whose "high whirling flames" were known to Sophocles; and of the volcano of Medina, which according to Burckhardt, still continued to pour out a stream of lava on the 2d of November, 1276.
*Sophocl., 'Philoct.', v. 971 and 972. On the supposed epoch of the extinction of the Lemnian fire in the time of Alexander, compare Buttmann, in the 'Museum der Alterhumswissenschaft', bd. i., 1807, s. 295; Dureau de la Malle, in Malte-Brun, 'Annales des Voyages', t. ix., 1809, p. 5; Ukert in Bertuch, 'Geogr. Ephemeriden', bd. xxxix., 1812, s. 361; Rhode, 'Res Lemnicae', 1829, p. 8; and Walter, 'Ueber Abnahame der Vulken. Thatigkeit in Historischen Zeiten', 1844, s. 24. The chart of Lemmos, constructed by Choiseul, makes it extremely probable that the extinct crater of Mosychlos, and the island of Chryse, the desert habitation of Philoctetes (Otfried Muller, 'Minyer', s. 300), have been long swallowed up by the sea. Reefs and shoals, to the northeast of Lemnos, still indicate the spot where the Aegean Sea once possessed an active volcano like Aetna, Vesuvius, Stromboli, and Volcano (in the Lipari Isles).
Every stage of volcanic activity, from its first origin to its extinction, is characterized by peculiar products; first by ignited scoriae, streams of lava consisting of trachyte, pyroxene, and obsidian, and by rapilli and tufaceous ashes, accompanied by the development of large quantities of pure aqueous vapor; subsequently, when the volcano becomes a solfatara, by aqueous vapors mixed with sulphureted hydrogen and carbonic acid gases; and, finally, when it is completely cooled, by exhalations of carbonic acid alone. There is a remarkable class of igneous mountains which do not eject lava, but merely devastating streams of hot water,* impregnated with burning sulphur and rocks reduced to a state of dust (as, for instance, the Galungung in Java); but whether these mountains present a normal condition, or only a certain transitory modification of the volcanic process, must remain undecided until they are visited by geologists possessed of a knowledge of chemistry in its present condition.
*Compare Reinwardt and Hoffmann, in Poggendorf's 'Annalen', bd. xii., s. 607; Leop. von Buch, 'Descr. des Iles Canaries', p. 424-426. The eruptions of argillaceous mud at Carguairazo, when that volcano was destroyed in 1698, the Lodazales of Igualata, and the Moya of Pelileo -- all on the table-land of Quito -- are volcanic phenomena of a similar nature.
I have endeavored in the above remarks to furnish a general description of volcanoes -- comprising one of the most important sections of the history of terrestrial activity -- and I have based my statements partly on my own observations, but more in their general bearing on the results yielded by the labors of my old friend, Leopold von Buch, the greatest geognosist of our own age, and the first who recognized the intimate connection of volcanic phenomena, and their mutual dependence upon one another, considered with reference to their relations in space.
Volcanic action, or the reaction of the interior of a planet on its external crust and surface, was long regarded only as an isolated phenomenon, and was considered solely with respect to the disturbing action of the subterranean force; and it is only in recent times that -- greatly to the advantage of geognostical views based on physical analogies -- volcanic forces have been regarded as 'forming new rocks, and transforming those that already existed'. We here arrive at the point to which I have already alluded, at which a well-grounded study of the activity of volcanoes, whether igneous or merely such as emit gaseous exhalations, leads us, on the one hand, to the mineralogical branch of geognosy (the science of the texture and the succession of terrestrial strata), and, on the other, to the science of geographical forms and outlines -- the configuration of continents and insular groups elevated above the level of the sea. This extended insight into the connection of natural phenomena is the result of the philosophical direction which has been so generally assumed by the more earnest study of geognosy. Increased cultivation of science and enlargement of political views alike tend to unite elements that had long been divided.
This material taken from pages 248-
COSMOS: A Sketch of the Physical Description of the Universe, Vol. 1 by Alexander von Humboldt
Translated by E C Otte
from the 1858 Harper & Brothers edition of Cosmos, volume 1
If, instead of classifying rocks according to their varieties of form and superposition into stratified and unstratified, schistose and compact, normal and abnormal, we investigate those phenomena of formation and transformation which are still going on before our eyes, we shall find that rocks admit of being arranged according to four modes of origin.
'Rocks of eruption', which have issued from the interior of the earth either in a state of fusion from volcanic action, or in a more or less soft, viscous condition, from Plutonic action.
'Sedimentary rocks', which have been precipitated and deposited on the earth's surface from a fluid, in which the most minute particles were either dissolved or held in suspension constituting the greater part of the secondary (or flotz) and tertiary groups.
'Transformed or metamorphic rocks',* in which the internal texture and the mode of stratification have been changed, either by contact or proximity with a Plutonic or volcanic endogenous rock of eruption,** or, what is more frequently the case, by a gaseous sublimation of substances*** which accompany certain masses erupted in a hot, fluid condition.
*[As the doctrine of mineral metamorphism is now exciting very general attention, we subjoin a few explanatory observations by the 'New Philos. Journ.', Jan., 1848: "In its widest sense, mineral metamorphism means every change of aggregation, structure, or chemical condition which rocks have undergone subsequently to their deposition and stratification, or the effects which have been produced by other forces than gravity and cohesion. There fall under this definition, the discoloration of the surface of black limestone by the loss of carbon; the formation of brownish-red crusts on rocks of limestone, sandstone, many slate structures, serpentine, granite, etc., by the decomposition of iton pyrites, or magnetic iron, finely disseminated in the mass of the rock; the conversion of anhydrite into gypsum, in consequence of the absorption of water; the crumbling of many granites and porphyries into gravel, occasioned by the decomposition of the mica and feldspar. In its more limited sense, the term metamorphic is confined to those changes of the rock which are produced, not by the effect of the atmosphere or of water on the exposed surfaces, but which are produced, directly or indirectly, by agencies seated in the interior of the earth. In many cases the mode of change may be explained by our physical or chemical theories, and may be viewed as the effect of temperature or of electro-chemical actions. Adjoining rocks, or connecting communications with the interior of the earth, also distinctly point out the seat from which the change proceeds. In many other cases the metamorphic process itself remains a mystery, and from the nature of the products alone do we conclude that such a metamorphic action has taken place.] -- Tr.
** In a plan of the neighborhood of Tezcuco, Totonilco, and Moran ('Atlas Geographique et Physique', pl. vii.), which I originally (1803) intended for a work which I never published, entitled 'Pasigrafia Geognostica destinada al uso de los Jovenes del Colegio de Mineria de Mexico', I names (in 1832) the Plutonic and volcanic eruptive rocks 'endogenous' (generated in the interior), and the sedimentary and flotz rocks 'exogenous' (or generated externally on the surface of the earth). Pasiward, [upward arrow] and the latter by the same symbol directed downward [downward arrow]. These signs have at least some advantage over the ascending lines, which in the older systems represent arbitrarily and ungracefully the horizontally ranged sedimentary strata, and their penetration through masses of basalt, porphyry, and syenite. The names proposed in the pasigraphico-geognostic plan were borrowed from De Candolle's nomenclature, in which 'endogenous' is synonymous with monocotyledonous, and 'exogenous' with dicotyledonous plants. Mohl's more accurate examination of vegetable tissues has, however, shown that the growth of monocotyledons from within, and dicotyledons from without, is not strictly and generally true for vegetable organisms (Link, 'Elementa Philosophiae Botanicae', t. i., 1837, p. 287; Endlicher and Unger, 'Grundzugeder Botanik', 1843, s. 89; and Jussieu, 'Traite de Botanique', t. i., p. 85). The rocks which I have termed endogenous are characteristically distinguished by Lyell, in his 'Principles of Geology', 1833, vol. iii., p. 374, as "nether-formed" or "hypogene rocks."
*** Compare Leop. von Buch, 'Ueber Dolomit als Gebirgsart', 1823, s. 36; and his remarks on the degree of fluidity to be ascribed to Plutonic rocks at the period of their eruption, as well as on the formation of gneiss from schist, through the action of granite and of the substances upheaved with it, to be found in the 'Abhandl. der Akad. der Wissensch. zu Berlin' for the year 1842, s. 58 und 63, and in the 'Jahrbuch fur Wissenschaftliche Kritik', 1840, s. 195.
'Conglomerates'; coarse or finely granular sandstones, or breccias composed of mechanically-divided masses of the three previous species.
These four modes of formation -- by the emission of volcanic masses, as narrow lava streams; by the action of these masses on rocks previously hardened; by mechanical separation or chemical precipitation from liquids impregnated with carbonic acid; and, finally, by the cementation of disintegrated rocks of heterogeneous nature -- are phenomena and formative processes which must merely be regarded as a faint reflection of that more energetic activity which must have characterized the chaotic condition of the earlier world under wholly different conditions of pressure and at a higher temperature, not only in the whole crust of the earth, but likewise in the more extended atmosphere, overloaded with vapors. The vast fissures which were formerly open in the solid crust of the earth have since been filled up or closed by the protrusion of elevated mountain chains, or by the penetration of veins of rocks of eruption (granite, porphyry, basalt, and melaphyre); and while, scarcely more than four volcanoes remaining through which fire and stones are erupted, the thinner, more fissured, and unstable crust of the earth was anciently almost every where covered by channels of communication between the fused interior and the external atmosphere. Gaseous emanations rising from very unequal depths, and therefore conveying substances differing in their chemical nature, imparted greater activity to the Plutonic processes of formation and transformation. The sedimentary formations, the deposits of liquid fluids from cold and hot springs, which we daily see producing the travertine strata near Rome, and near Hobart Town in Van Diemen's Land, afford but a faint idea of the flotz formation. In our seas, small banks of limestone, almost equal in hardness at some parts to Carrara marble,* are in the course of formation, by gradual precipitation, accumulation, and cementation -- processes whose mode of action has not been sufficiently well investigated.
Darwin, 'Volcanic Islands', 1844, p. 49 and 154.
The Sicilian coast, the island of Ascension, and King George's Sound in Australia, are instances of this mode of formation. On the coasts of the Antilles, these formations of the present ocean contain articles of pottery, and other objects of human industry, and in Guadaloupe even human skeletons of the Carib tribes.*
*[In most instances the bones are dispersed; but a large slab of rock, in which considerable portion of the skeleton of a female is embedded, is preserved in the British Museum. The presence of these bones has been explained by the circumstance of a battle, and the massacre of a tribe of Gallibis by the Caribs, which took place near the spot in which they are found, about 120 years ago; for, as the bodies of the slain were interred on the sea-shore, their skeletons may have been subsequently covered by sand-drift, which has since consolidated into limestone. Dr. Moultrie, of the Medical College, Charleston, South Carolina, U.S., is, however, of opinion that these bones did not belong to individuals of the Carib tribe, but of the Peruvian race, or of a tribe possessing a similar craniological development.] --Tr.
The negroes of the French colonies designate these formations by the name of 'Maconne-bon-Dieu'.*
Moreau de Jonnes, 'Hist. Phys. des Antilles', t. i., p. 136, 138, and 543; Humboldt, 'Relation Historique', t. iii., p. 367.
A small colitic bed, formed in Lancerote, one of the Canary Islands, and which, notwithstanding its recent formation, bears a resemblance to Jura Limestone, has been recognized as a product of the sea and of tempests.*
*Near Teguiza. Leop. von Buch, 'Canarische Inseln', s. 301.
Composite rocks are definite associations of certain crytonostic, simple minerals, as feldspar, mica, solid silex, augite, and nepheline. Rocks very similar to these consisting of the same elements, but grouped differently, are still formed by volcanic processes, as in the earlier periods of the world. The character of rocks, as we have already remarked is so independent of geographical relations of space,* that the geologist recognizes with surprise, alike to the north or the south of the equator, in the remotest and most dissimilar zones, the familiar aspect, and the repetition of even the most minute characteristics in the periodic stratification of the silurian strata, and in the effects of contact with augitic masses of eruption.
*Leop. von Buch, op. cit., p. 9.
We will now enter more fully into the consideration of the four modes in which rocks are formed -- the four phases of their formative processes manifested in the stratified and unstratified portions of the earth's surface; thus, in the 'endogenous' or 'erupted rocks', designated by modern geognosists as compact and abnormal rocks, we may enumerate the following principal groups as immediate products of terrestrial activity:
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End of part 15 of 21
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