'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.
p 238
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.*
[footnote] *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
p 239
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.*
[footnote] (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.
[footnote] *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
p 240
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.
[footnote] *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.*
[footnote] *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.
p 241
Santorino is the most important of all the 'islands of eruption' belonging
to volcanic chains.*
[footnote] *[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
p 242
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."*
[footnote] *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.**
[footnote] *Appearance of a new island near St. Miguel, one of the Azores,
11th of June, 1638, 31st of December, 1719, 13th of June, 1811.
[footnote] **[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.*
[footnote] *Prevost, in the Bulletin de la Societe Geologique, t. iii., p.
34; Friedrich Hoffman, 'Hinterlassene Werke.' bd. ii., s. 451-456.
p 243
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
p 244
neighboring sea?"**
[footnote] *"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."
[footnote] **[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
p 245
with the hypothesis of the decomposition of great masses of water?**
[footnote] * 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.
[footnote] ** [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.
[footnote] *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.
[footnote] *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.