Popular Science Monthly/Volume 67/October 1905/Greek Ideas of Vulcanism
|GREEK IDEAS OF VULCANISM.|
'GREEK philosophy was born' as has been aptly remarked, 'on that day when some thinker tried to find a rational explanation of the universe.' Tradition awards the honor of this initiative to Thales of Miletus, who lived in the beginning of the sixth century, B.C. Meager and unsatisfactory as is our knowledge of this early pioneer, his place is none the less honored and secure in the history of natural philosophy. According to common report he was well versed in the astronomical lore of the Chaldeans, predicted eclipses, investigated meteorological phenomena, sought to explain the causes of earthquakes, and attained to the truly sublime height of conceiving that all existing things had a common origin, and that water was the primordial matter of the universe.
In the teachings of Thales and his followers we discover not only germs of suggestion destined to become extremely fruitful in biological science, but also the first serious attempts at geological speculation during classical antiquity. Previous to the sixth century b.c., neither the Hellenic, Egyptian nor Oriental mind seems to have advanced beyond intellectual childhood in proposing to itself a rational explanation of nature. The ancient feeling for nature amongst the Greeks, as revealed in literature, was decidedly prosaic and practical; only by slow degrees did they come to the idea of nature as a single power or being, more or less personified, and possessing the attributes of beauty and conscious intelligence. With the earlier deistic interpretation of nature, with the numerous legends and 'observation myths' of antiquity, and with the invocation of supernatural agencies by way of explaining vulcanism, we are not now especially concerned. Merely be it noted in passing that the localization of geological myths, such as that of the Chimæra, the Deucalion deluge, the fall of Hephæstus upon Lemnos together with his various subterranean forges, and also significant place-names like Rhegium, Tempe, Piræus, Kaimeni, Katakekaumene ('Burnt Country'), etc., frequently attests the occurrence of geological events which were afterwards forgotten.
Volcanoes themselves did not at first engage the attention of Ionian philosophers, for reasons easily understood. In the first place, the eruptions known to have taken place in the Greek Archipelago occurred either at the very dawn of Hellenic culture, or during its wane. Secondly, the mainland on either side of the Ægean being free from volcanic action, knowledge of this form of energy was dependent upon the reports of travelers who had visited Etna or Argæus; and our sole reason for supposing that either of these centers was in eruption during the early historical period is based upon their persistent association with Typhon myths. As for the first tremendous convulsion which overwhelmed Thera (Santorin), this happened so long anterior to documentary history that not the least vestige of a tradition has survived. The next fiery outbreak did not occur until about two hundred years before our era, and that of Methona only about a century earlier. Hence, until considerably after the time of Aristotle, the opportunity for studying active volcanoes, either near at hand or in distant regions, was extremely limited.
On the other hand, secondary manifestations of vulcanism were everywhere abundant. The extraordinary prevalence and violence of earthquakes throughout the ancient world, their effect upon the popular mind, and the extent to which even historical events were influenced by them, are facts too well known to require comment. Frequent references in literature to mud volcanoes, solfataras, fumaroles, sulphur springs and allied phenomena reveal a lively curiosity in these matters, and a growing tendency to associate them with volcanic action. Attention early became attracted to the numerous jets of mephitic vapor in western Phrygia, their fancied connection with the infernal regions giving rise to such names as Charonia and Plutonia. The Plutonium of Hierapolis was particularly famous, and so too were the hot springs in various parts of Greece, as at Thermopylæ, and in the north of Eubœa. All these occurrences were associated in the olden time with Heracles in his character of fire-god; and owing to constant succession of earthquake shocks in the Peloponnese, that district became the focus of the worship of Poseidon, the 'earth-shaker.' Gradually a mythological interpretation of these phenomena gave place to a philosophical, crude at first, but elaborated little by little, until finally ideas were developed which have become the heritage of modern science.
It will repay us to trace the development of some of these ideas, though in view of the thoroughness with which this has already been done by Sudhaus in his scientific commentaries on 'Ætna' (Leipzig, 1898), we need not attempt here more than a cursory retrospect. After Thales, who regarded earthquakes as universal disturbances produced
by movements of the underlying support of the earth's crust, the next to expound their origin was Anaximander, always supposing that the disciple of Thales has not been confused with some later writer in the following passage from Ammianus (xvii. 7, 12):
Neither Anaximander, Archelaus nor Xanthus is mentioned by Aristotle in connection with earthquakes or volcanoes, although their opinions have been preserved by other writers. Briefly, the two leading theories before Aristotle's time to account for seismic movements were these: The first, which is attributed to Anaximines, referred them to fractures in the earth's crust which were produced by its passing through a process of drying, after having been previously saturated with moisture. The other was that of Anaxagoras, who believed that they were caused by the fiery elements of the ether, as well as by confined masses of water, which had penetrated into the interior of the earth, and were struggling to escape thence. In a modified form of the same theory, Democritus and Archelaus attached special significance to confined air as a cause of earthquakes, and this agency was still further insisted upon by Aristotle.
It will be noted that both of these theories contain potential germs of suggestion. That of Anaximines, according to which the crust caves in, owing to the splitting of underlying rocks after periods of extreme dryness, foreshadows the modern contraction hypothesis. Excluding, as this view does, the idea of any connection between seismic and volcanic disturbances, the later theory of Anaxagoras directly favors it; and in the hands of the great Stagyrite this connection became the leading feature in the discussion of the question. According to Aristotle, both forms of subterranean disturbances were due to the action of winds (or gases, as we should probably say) which were confined beneath the earth's surface and were endeavoring to find a vent. The element of fire which appears in volcanic eruptions was explained at the result of vapors becoming rarefied and thereupon igniting. Imperfect as this theory may seem, it subsequently met with general acceptance and after slumbering for many centuries, was revived by Cecco d'Ascoli, contemporary of Dante, when Italy again caught the reflection of Greek learning. Posidonius, Strabo, Ovid, Pliny, and the unknown author of 'Ætna' whom some have sought to identify with Lucilius junior, all were influenced by Aristotle's view. Ovid, for instance, in his description of the upheaval of the promontory of Methana in the Argolis peninsula, which happened about the year 282 B.C., likens the process to the inflation of a bladder: "The earth," he says, "became distended by the force of impregnated vapor like a bladder filled with air, or like the skin of a goat." A like influence is betrayed also in the beautiful poem of Lucretius, where the following explanation is offered (VI., 639-702): "Ætna emits its flames in this way: caverns of rock run under it, full of wind which heats first itself and then the rocks with which it comes in contact, and then bursts out with flame, ashes, smoke and huge stones. Again, caverns reach from the sea to the mountain; through these pass from the sea both water and wind mixed; this wind and water force up flame and rocks and clouds of sand."
By more careful observation of these occurrences it was further established that volcanoes served as a vent in consequence of which the frequency and violence of earthquake shocks were diminished. Thus, Strabo remarks that the destructive shocks to which the island of Eubœa was subject, ceased when an eruption took place in the plain of Lelanto, near the city of Chalcis. Again, he explains the cessation in Southern Italy of any such convulsions as were supposed to have separated Sicily from the mainland by the formation in that region of cones of eruption, like those of the Lipari Islands. Elsewhere he uses the term of 'breathing holes' in reference to such cones. That he had a clear understanding of this feature is evident from the following passage:
Notwithstanding our indebtedness to Strabo for many interesting details concerning Etna and other volcanic districts, to say nothing of his luminous remarks on the elevation and subsidence of land-masses, he does not seem to have advanced any original explanations of physical phenomena, but merely to have re-echoed those of his predecessors, foremost of whom were Aristotle and Posidonius. Indeed, it is no exaggeration to say that nearly all of Strabo's physiographic ideas were inspired directly by these marvelously keen investigators. The influence of Posidouius, certainly one of the most intelligent travelers of antiquity, upon writers in all departments of science is particularly marked. Strabo has preserved for us his observations in connection with Etna eruptions, with the elevation of volcanic islands, with earthquakes which happened in Phœnicia, and with a great variety of phenomena, sometimes in considerable detail, and in terms which agree closely with those of modern experience. The following graphic description of the formation of a new volcanic orifice amongst the Lipari Islands may suffice for an example:
Accounts of the upheaval and disappearance of volcanic islands in the Mediterranean are by no means rare in classic literature, probably the best known example being that already alluded to in connection with Thera in the year 197 B.C. On this occasion, a number of reports tell us, flames rose from the water for four days between Thera and the neighboring Therasia, so that the whole sea boiled and blazed; and little by little an island was ejected, being lifted as it were by mechanical force, and composed of volcanic rock extending over an area of twelve stadia in circumference. It is now generally admitted that the Santorin group is the basal wreck of a very large and ancient volcanic mountain, the eruptive history of which is comparatively well known. Prior to the sharp outbreak which occurred in 1866, memorable in geological annals, it was supposed that the eruption of 197 B.C. was the earliest which can be associated with the period of its human occupancy. Shortly after the last outbreak, however, relics of an ancient civilization were discovered in the islands of Thera and Therasia, buried beneath a layer of pumice-stone and other volcanic debris. As to the period of culture indicated by these remains, archeologists are agreed in referring them to the Proto-Mycenæan, which is supposed to antedate our present era by at least 2,000 years.
Eloquent testimony exists in classic literature that men were profoundly impressed even in earliest times by the class of phenomena typified by Thera and the mythical Atlantis. From the rise and disappearance of islands, sometimes in connection with vulcanism, sometimes as the result of other causes, thinkers were led to conceive the possibility of large land-masses, or even continents, undergoing elevation and subsidence. Areas were known which the sea had invaded, and other tracts were pointed out where submergence was plainly indicated. Thus Xenophanes, in the sixth century b.c., and after him Xanthus, Eratosthenes, Herodotus and others, not only entertained the idea of continental subsidence, but interpreted fossil remains of marine animals as evidence of former submergence. When we come to Aristotle, Posidonius and Strabo, we find that their opinions concerning oscillations of the sea-level and other progressive changes of the earth's surface are worthy of modern geologists. This phase of the subject has been so ably treated by Lyell in his 'Principles of Geology,' by Lasaulx, in his 'Geology of the Greeks and Romans,' and more recent writers, that it must be more or less familiar to all. That which is important to remember, however, is that local manifestations of vulcanism, dispersed over a wide region, and isolated examples of inconstancy of the sea-level, should have been viewed from the uniformitarian standpoint at a period so far antedating our own, should have been reduced to a general system, and should have led to the framing of hypotheses to account for them which have a singularly modern aspect. One can not but marvel that some of the most difficult problems in geology were solved by rational methods, and in the main accurately, by those ardent questioners of nature who often seem to have grasped intuitively that which has cost the rest of the world centuries of patient effort to rediscover.
The limits assigned to the present article do not permit us to examine Roman contributions to the study of vulcanism, interesting as such an inquiry would be. Nor have we attempted in this sketch to enumerate all of the lesser luminaries of Greek science who assisted, either by accumulation of facts, or by cleverness in putting them together, toward a fuller understanding of important principles of geology. Archelaus, Diogenes of Apollonia, Metrodorus of Chios, author of a famous 'Treatise on Nature,' Empedocles, whom a characteristic but probably apochryphal narrative reputes to have perished in Etna's crater,—these and various others have been passed over in silence. Enough has been said, however, to indicate the general trend of investigation and some of its fruitful conclusions. This brief sketch will have succeeded in its purpose if any shall become interested to pursue the subject independently in its details. Such retrospect has not only a broadening value, but is well-nigh incumbent upon all who would escape the fate against which Goethe so energetically warns us:
Wer nicht von dreitausend Jahren
Sich weiss Rechenschaft zu geben,
Bleibt im Dunkeln, unerfahren,
Mag von Tag zu Tage leben.
- It has been suggested with much plausibility that all the traditions of certain islands in the Mediterranean having at some time or other shifted their positions, and at length become stationary, originated in the great change produced in their form by earthquakes and submarine eruptions, of which there have been many modern examples in the new islands raised in the time of history. When the series of convulsions ended, the island was said to become fixed. Cf. Lyell, 'Principles of Geology,' Vol. I., Chapter 1, and Emerson's vice-presidential address on 'Geological Myths,' Proc. Amer. Assoc. Adv. Sci., 1897. Abundant references to the literature will be found in the first part of Max Mayer's 'Die Giganten und Titanen in der antiken Sage und Kunst' (Berlin, 1887)
- Metam., XV., 296-306. Pliny ('Nat. Hist.,' II., 192) also gives his adherence to the same view.
- Strabo, VI., 1, 6.
- Ibid., I., 3, 16.
- Compare, for instance, the estimates given by M. Dubois, in his 'Examen de la Géographie de Strabon' (Paris, 1891), and S. Sudhaus, in his interesting essay on 'Ætna' (Leipzig, 1901).
- Strabo, VI., 2, 11. Compare also the similar accounts given by Pliny ('Nat. Hist.,' II., 19) and Aristotle ('Meteor.,' II., S, 19).