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Alexander von Humboldt: „On the Constitution and Mode of Action of Volcanoes, in different parts of the Earth“, in: ders., Sämtliche Schriften digital, herausgegeben von Oliver Lubrich und Thomas Nehrlich, Universität Bern 2021. URL: <https://humboldt.unibe.ch/text/1823-Ueber_den_Bau-03-neu> [abgerufen am 20.04.2024].
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| Titel | On the Constitution and Mode of Action of Volcanoes, in different parts of the Earth | ||||||
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| Jahr | 1823 | ||||||
| Ort | New York City, New York | ||||||
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Nachweis in: The Minerva 2:29 (25. Oktober 1823), S. 229, 2:30 (1. November 1823), S. 237, 2:31 (8. November 1823), S. 245–246, 2:32 (15. November 1823), S. 253–254, 2:33 (22. November 1823), S. 261–262.
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| Sprache | Englisch | ||||||
| Typografischer Befund | Antiqua; Spaltensatz; Auszeichnung: Kursivierung. | ||||||
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|229|
|Spaltenumbruch|
When we consider the influence whichscientific travels into distant
regions, anda more extended geographical knowledge,have for some
centuries past exertedupon the study of nature, we soon dis-cover
how this influence has varied ac-cording to the objects of inquiry,
whichhave been, on the one hand, the forms ofthe organic world,
and, on the other, theinanimate formation of the
earth;—theknowledge of rocks, their relative ages,and
origin. Different forms of plantsand animals enliven the earth in
everyzone, as well in the plains, where theheat of the atmosphere
is determined bythe geographical latitude and the
differentinflexions of the isothermal lines, as whereit changes
suddenly on the steep declivi-ties of the mountains. Organic
naturegives a peculiar physiognomical characterto every zone,
which is not the case withthe inorganic world where the solid
crustof the earth is divested of its vegetablecovering. The same
rocks approach-ing to and receding from each other ingroups occur
in both hemispheres, fromthe equator to the poles. On a
distantisland, surrounded by strange plants, un-der a sky where
the well-known stars donot shine, the sailor recognises, oftenwith
glad surprise, the clayslate which isthe common rock of his native
country.
This independence of the geognosticalrelations of places on the present
con-stitution of their climate, does not diminish,but only gives a
particular direction to thefavourable effect upon the progress
ofgeology and physical geognosy, which isproduced by numerous
observations madein foreign countries. Every expeditionenriches
natural history with new plants,and new genera of animals; at one
timethey are organic forms ranging them-selves with well-known
types, and repre-senting to us, in its original perfection,
aregularly woven, though often apparentlyinterrupted texture of
animated crea-tures; at another, they are forms whichappear to be
insolated, as vestiges ofgenera which have been destroyed, or
as|Spaltenumbruch|surprising members of groups still to bediscovered. Such a
variety is not pre-sented by the examination of the solidcrust of
the earth; it rather reveals tous an agreement, which excites the
admi-ration of the geognost, between the partsof which it is
composed, in the superpo-sition of masses of different natures,
andin their periodical repetition. In thechain of the Andes, as
well as in thecentral mountains of Europe, one forma-tion seems,
as it were, to occasion theexistence of another; masses of the
samecharacter assume similar forms: moun-tains are formed by
basalt and dolerite;steep declivities by dolomite, porphyry,and
quadersandstein; bell-shaped emi-nences and high-vaulted domes by
vitre-ous trachyte rich in felspar.
In the most distant zones, larger crys-tals, as it were by internal evolution outof the more compact texture of the greatermass, aggregate into subordinate beds,and thus frequently announce the vicinityof a new and independent formation.Thus is the whole inorganic world re-flected, more or less clearly, in everymountain of considerable extent; but inorder to ascertain completely the mostimportant phenomena respecting the com-position, the relative age, and the originof the different species of rocks, observa-tions from the most distant parts of theearth must be compared together. Pro-blems which had appeared enigmatical tothe geognost in his mother country aresolved near the equator. If distantzones do not furnish new species ofrocks, that is to say, unknown arrange-ments of simple substances, as has alreadybeen remarked, they yet teach us howto discover the great laws which areevery where the same, and according towhich, the different strata of the earthsupport each other, appear in the formof veins, or are elevated by elastic pow-ers.
We need not be surprised, that not-withstanding the great assistance
whichour geological information derives frominquiries, having
whole countries fortheir object, an extensive class of phe-nomena
(with which I venture to enter-tain this assembly,) has been
treated,during so long a period, in a confinedmanner; the points
of comparison beingmore difficult, and, I might say,
moretroublesome to find. Whatever we be-lieved we knew, until the
end of the lastcentury, respecting the form of volcanoes,and the
action of their subterraneousforces, had been derived from two
moun-tains of the south of Italy, from Ætna andfrom
Vesuvius. The first being moreaccessible, and having, like all low
volca-noes, more frequent eruptions, has servedfor a type,
according to which a wholedistant world,—the powerful
volcanoesof Mexico, South America, and the Asi-atic Islands, has
been considered. Sucha method recalls to our remembrancethe
shepherd of Virgil, who expected hisnarrow cottage to contain the ideal
of theeternal city, imperial Rome.
A careful examination of the wholeMediterranean, and principally of
itseasterly islands and shores, where man-kind first awakened to
mental culture,and to noble feelings, might certainlyhave
dispelled such a narrow idea ofnature. Out of the deep bed of the
sea,among the Sporades, rocks of trachytehave arisen, like the
Azoric island,which has thrice reappeared during threecenturies,
the intervening periods beingalmost equal. Between Epidaurus
andTroezene, near Methone, the Pelopon-nesus has a Monte Nuovo,
which hasbeen described by Strabo, and seen byDodwell, higher than
the Monte Nuovoof the Campi Phlegræi, near Baia; per-haps
higher than the new volcano ofXorullo in the plains of Mexico, which
Ihave found among a thousand basalticcones, raised out of the
earth, and stillsmoking. In the basin of the Mediter-ranean Sea
also, the volcanic fire bursts|Spaltenumbruch|forth, and not only from permanent
cra-ters, from insolated mountains which pre-serve a lasting
communication with theinterior of the earth, like
Stromboli,Vesuvius, and Ætna;—on Ischia, nearthe
Epomæus, and also, as it would ap-pear from the reports of the
ancients,near Chalcis in the Lelantic plains, haslava flowed out
of fissures which havesuddenly opened. Besides these phe-nomena,
which have taken place in theperiod of history within the narrow
limitsof certain traditions, and which Ritterwill collect and
explain in his masterlyGeography, the shores of the Mediterra-nean
contain abundant remains of moreancient igneous effects. The south
ofFrance shows, in Auvergne, a range ofhills, in which bells of trachyte occuralternately with cones
of eruption, fromwhich currents of lava have descended.The
Lombardic plain, which forms theinnermost bay of the Adriatic Sea,
sur-rounds the trachyte of the EuganeanHills, where domes of
granular trachyte,of obsidian, and of pearlstone, rise,
which,passing into each other, break throughthe Jura limestone,
but never occur innarrow streams which have flowed.Similar
evidences of former revolutionsmay be found in many parts of the
Gre-cian continent, and in Asia Minor, coun-tries which will
afford the geognost copi-ous subjects for examination, when
thelight once returns to the land whence itfirst beamed over the
western world—when tormented mankind ceases to sinkunder
the savage lethargy of the Ottoman.
I mention the geographical neighbour-hood of so many phenomena, in order toprove, that the bed of the Mediterranean,with all its chains of islands, might haveafforded to the attentive observer, everything that has been discovered, in latterperiods, under the most varied forms, inSouth America, on Teneriffe, or on theAleutian islands, near the polar regions.There were accumulated objects forobservation, but tours into distant re-gions, and the comparison of large tractsof country within and beyond Europe,were necessary, in order to discoverwhat was common to all these phenomena,and to learn, clearly, their dependenceon each other.
|237|
|Spaltenumbruch|
By the usage of language, which oftengives stability and respect to the
firsterroneous views of things, but often, as itwere, by instinct,
distinguishes the truth,we apply the term volcanic to all
erup-tions of subterranean and melted matter;to columns of smoke
and steam, whichrise sporadically out of rocks, as at Co-lares
after the great earthquake at Lis-bon; to Salsæ, or conical
hills of claywhich emit mud, asphaltum, and hydro-gen, as those
near Girgenti, in Sicily, andnear Turbaco, in South America; to
hotGeyser springs which rise by the pressureof elastic vapours;
and, in general, to allviolent powers of nature which havetheir
seat deep in the interior of ourplanets. In the Spanish main of
America,and in the Philippine islands, the inhabi-tants make a
distinction between igneous|Spaltenumbruch|and aqueous volcanoes, vulcunes de aguay de fuego: they apply the
first name tomountains, which, during violent earth-quakes, from
time to time, eject subter-raneous water, and with a dull noise.
Without denying the connexion be-tween the different phenomena just men-tioned, it seems advisable to give a dis-tinct language to the physical as well asto the oryctognostic branch of geognosy;and not to apply the term volcano in oneinstance to a mountain that terminates ina permanent crater; and in another, toevery subterranean cause of volcanicphenomena.
In the present state of the earth, themost common form of volcanic
eminencesis that of isolated cones; such are Vesu-vius,
Ætna, the Peak of Teneriffe, Tun-guragua, and Cotopaxi. I have
seenthem of every magnitude, from the low-est hills to mountains
rising to the heightof 17,700 feet above the level of the
sea.Besides these conical mountains, thereare other craters,
permanently communi-cating with the interior of the earth,
situ-ated upon lengthened craggy ranges ofmountains, not always in
the middle oftheir wall-like summits, but towards theend, and near
their declivities. Such isPichincha which rises between the
Paci-fic Ocean and the town of Quito, and whichhas become
celebrated by Bouguer’searliest formula for the barometer;
suchalso are the volcanoes that rise in theplain de los Pastos, at
the elevation of10,000 feet. All these differently formedsummits
consist of trachyte, or trap-porphyry, a granular rock, full of
cracksand fissures, and composed of glassy fel-spar and
hornblende, but often containingin addition, augite, mica, laminar
felspar,and quartz.
Where the evidence of the first erup-tion, and where the first scaffolding, Imight say, has been entirely preserved,the isolated conical hills are surroundedby a high wall of rocks forming a circus,consisting of superposed strata; suchwalls, or annular surrounding masses, arecalled craters of elevation; of these veryimportant phenomena, Leopold vonBuch, the first geognost of our times,from whose works I have taken severalviews contained in this paper, read a re-markable account, five years ago.
The volcanoes which communicatewith the atmosphere by means of craters,and the conical hills of basalt and bell-shaped trachytic hills without craters,the latter either low like Sarcouy, orhigh like Chimborazo, form differentgroups. A geographical comparisonshows, in one place, small Archipelagi,or, as it were, classed systems of moun-tains, either with craters and currents oflava, as in the Canaries and Azores, ordevoid of craters and real currents oflava in the Euganeans, and the Sieben-gebirge near Bonn; or it shows, in otherplaces, single and double chains of vol-canoes, connected with each other, andforming tracts of many hundred miles inlength, which are either parallel to thedirection of the mountains, as in Guati-mala, Peru, and Java, or in directionsperpendicular to their axis, as in the landof the Aztekes, where none but volcanictrachyte-mountains attain the limits ofeternal snow, and those, probably, havebeen thrust out of a fissure nearly 500miles in length, which divides the wholecontinent, from the Pacific Ocean tothe Atlantic.
This aggregation of volcanoes either insingle round groups, or in double
ranges,affords the most determinate proof thatvolcanic effects do
not depend upon slightcauses existing near the surface of
theearth, but that they are great and deeplyfounded phenomena. The
whole easternpart of the American continent, which ispoor in
metals, is at present without cra-ters, without trachyte, probably
evenwithout basalt. All the volcanoes aresituated in the part
opposite to Asia, inthe meridian line of the Andes chain,|Spaltenumbruch|1800
geographical miles long; the wholeof the elevated district of Quito is
nothingbut a single volcanic hearth, the summitsof which are
Pichincha, Cotopaxi, andTunguragua. The volcanic fire nowbursts
from one, and then from anotherof these apertures, which we are
accus-tomed to consider as separate volcanoes.
The progressive motion of the firehere, in the space of three centuries,turned from north to south. The earth-quakes with which this part of the worldis so terribly visited, furnish remarkableevidences of the existence of subter-raneous communication, not only be-tween countries without volcanoes, aswas known long ago, but even betweencraters which are far distant from eachother. Thus the volcano of Pasto, situ-ated to the east of the river Guaytara, un-interruptedly vomited a high column ofsmoke, during the three months of theyear 1797; and this column disappearedat the very moment, when, at the dis-tance of nearly 300 miles, the greatearthquake of Riobamba and the muderuption of the Moya, killed from 30,000 to40,000 Indians. The sudden appearanceof the Azoric island Sabrina, on the 30thof January, 1811, was the forerunner ofthose dreadful shocks, which, further tothe west, shook, almost uninterruptedly,from the month of May, 1811, to thatof June, 1813, first the Antilles, after-wards the plains of the Ohio and the Mis-sissippi, and at last the opposite coast ofVenezuela. Thirty days after the com-plete destruction of the town of Carac-cas, the eruption of the volcano of St.Vincent in the neighbouring Antillestook place; at the same moment whenthis explosion happened, on the 30th ofApril, 1811, a subterranean noise washeard throughout a country of 2200geographical square miles, or 47,900English square miles, in extent.
The inhabitants near the Apure, whereit is joined by the Rio Nula, as well asthose of the most distant part of thecoast, compared this noise to that of ar-tillery. From where the Rio Nula fallsinto the Apure, through which river Icame into the Orinoco, to the volcano ofSt. Vincent, the distance, in a direct line,is 731 English miles. The noise justalluded to, which certainly was not com-municated through the air, must, there-fore, have had a deep internal cause. Itsintensity on the coast of the Antillic seawas scarcely greater than in the interiorof the country.
It would be useless to augment thenumber of examples, but for the purposeof recalling to memory a phenomenonwhich has become historically interestingto Europe, I will mention the earthquakeat Lisbon. At the same time with this,on the 1st of November, 1755, not onlywere the Swiss lakes, and the sea on theSwedish shores violently agitated, buteven in the easternly Antilles, aroundMartinque, Antigua, and Barbadoes,where the tide never exceeds 28 inches,it suddenly rose to 20 feet. All thesephenomena prove, that the subterraneanpowers act either dynamically, by pro-ducing tension and vibration, as in earth-quakes; or chemically, by producing oraltering substances, as in volcanoes.They prove, likewise, that these powersdo not act from superficial causes, fromthe exterior crust of the earth; but fromdeeply-seated causes, from the interiorof our planet; extending their simulta-neous effects to the most distant parts ofthe earth, through fissures and emptyveins.
|245|
|Spaltenumbruch|
The more different the structure ofvolcanoes; that is to say, of those
raisedmasses which surround the canal throughwhich the melted
substances proceedfrom the interior of the earth to its sur-face,
the more important is it to becomethoroughly acquainted with that
struc-ture by exact measurement. The in-terest attached to this
measurement,which has been a particular object of myexamination in
another part of the world,is heightened by the consideration,
thatthat which is to be measured is a varia-ble magnitude. The
physiognomy ofnature consists in the change of pheno-mena tending
to connect the present withthe past. In order to ascertain a
periodi-cal return, or the laws of progressive natu-ral changes in
general, certain fixed pointsare necessary; and observations
careful-ly made at stated periods, may serve fornumerical
comparison. Had the meantemperature of the atmosphere in
differ-ent latitudes been observed for a few thou-sand years, and
the mean height of thebarometer at the level of the sea, wemight
now know in what proportion theheat of different climates has
increased,or diminished, and whether the height ofthe atmosphere
has undergone anychanges. Similar points for comparisonare
required, for the variation and thedeclination of the magnetic needle,
andfor the intensity of the electromagneticpower, upon which two
excellent philo-sophers of this Academy have thrown somuch light.
If it be a praiseworthy un-dertaking of learned societies to
inquireassiduously into the changes of tempera-ture undergone by
the globe, into thosewhich take place in the pressure of
theatmosphere, and in the magnetic varia-tion,—it is the
duty of a travelling ge-ognost, in ascertaining the inequalityof
the earth’s surface, to consider, prin-cipally, the variable
height of the vol-canoes. What I formerly attempted onthe
mountains of Mexico, on the Tolu-ca Nauhiampatepetl and Xorullo, and
inthe Andes of Quito, on the Pichincha, Ihave found opportunity,
since my returnto Europe, to repeat at different periodson
Vesuvius. Saussure measured thismountain in 1773, at the time when
bothsides of the crater, the south-easternand north-western,
appeared to be ofequal altitude; he found their height tobe 609
toises (3894 feet) above the levelof the sea. The eruption of 1794
occa-sioned a fall on the south side, whicheven the unaccustomed
eye discovers ata great distance. In 1805, I measuredVesuvius
three times, in conjunction withM. von Buch, and M. Gay-Lussac;
wefound the elevation of the northern edge,opposite to Monte
Somma, la Rocca delPalo, to be exactly the same as Saussurehad
before determined it; the southern|Spaltenumbruch|edge we found 71 toises (454
feet) low-er than it was in 1773; the total heightof the volcano
on the side opposite Tor-re del Greco (towards which side thefire
seems to have acted the most power-fully, during the last 30 years,)
had di-minished one-ninth part.
The cone of ashes on Vesuvius bearsthe proportion of one-third to the heightof the whole mountain, that on Pichinchais as 1 to 10, and that on the Peak ofTeneriffe as 1 to 22; Vesuvius has,therefore, the largest cone of ashesin proportion, because, probably, as alow volcano, it has acted principallythrough its summit. A few months ago,I succeeded not only in repeating my for-mer measurements on Vesuvius, but alsoin ascertaining the elevation of all theedges of the crater. This work, per-haps, deserves some consideration, forthe periods at which it was executed in-clude those of the great eruptions from1805 to 1822, and it is, perhaps, the onlyadmeasurement yet published of any vol-cano which may be compared in all itsparts. It proves that the edges of thecraters, not only where they evidentlyconsist of trachyte, as in the volcanoes ofthe Andes, but likewise every whereelse, are much more constant phenomenathan has hitherto been believed. Simpleangles of elevation ascertained from thesame points are more proper for theseexaminations than barometrical and tri-gonometrical measurement. According tomy last determination, the north-westernedge of the crater of Vesuvius has notchanged its form in the least since Saus-sure’s time, a period of 49 years. Thesouth-eastern edge towards Bosche treCase, which became about 450 feet low-er in 1794, has sunk very little since thattime.
If in the description of great eruptions,in the public papers, the
completelychanged form of Vesuvius has frequentlybeen mentioned,
if this opinion oftenseems to be corroborated by the pictu-resque
views of the mountain made atNaples, the cause of this mistake may
befound in the circumstance, that the out-lines of the edges of
the crater havebeen confounded with those of the coneof eruption
which is accidentally formedin the middle of the crater, upon a
bot-tom that has been raised by vapours.Such a cone of eruption,
consisting ofrapilli and slags loosely heaped together,has become
visible over the south-east-ern edge of the crater, since 1816
and1818. The eruption of February, 1822,had so much increased it
that it had be-come from 70 to 80 feet higher than
thenorth-eastern edge of the crater, Roccadel Palo. This
remarkable cone, which,at Naples, they were accustomed to
con-sider as the true summit of Vesuvius,fell in with a tremendous
noise, during theeruption of the 22d of October, so thatthe bottom
of the crater, which had beenuninterruptedly accessible from the
year1811, now lies 850 English feet beneaththe northern edge, and
about 213 feetdeeper than the southern edge of the vol-cano. The
variable form and relativesituation of the crater of eruption,
theopening of which must not be taken forthe real crater of the
volcano, as fre-quently has been done, gives, at differenttimes, a
peculiar physiognomy to Vesu-vius; and the historiographer of
thatvolcano, from the mere outline of thesummit, and the relative
height of thenorthern or southern side of the moun-tain, as it is
drawn in Hackert’s Views inthe palace Portici, would guess the
yearin which the artist made the sketch ofhis picture.
In the night between the 23d and 24thof October, one day after the fall
of thecone of slags 400 feet in height, whensmall but numerous
currents of lava hadalready flowed, the fiery eruption of ashesand
rapilli began. It continued uninter-ruptedly for twelve days, but was
mostviolent during the first four. During this|246|time the detonations in the interior of thevolcano
were so violent, that the mereconcussion of the air (no earthquake
hadbeen observed) caused the roofs to burstin the palace of
Portici. In the sur-rounding villages of Resina, Torre delGreco,
Torre del Annonciata, and Boschetre Case, an interesting
phenomenonwas observed; the atmosphere was sothickly filled with
ashes, that the mostintense darkness overspread the wholecountry
for several hours in the middleof the day. The people walked in
thestreets with lanterns, as is often done atQuito when Pichincha
is in eruption.The flight of the inhabitants was nevermore
general; currents of lava wereless feared than a fall of ashes, a
pheno-menon which was unknown there withsuch violence, and in
consequence of therelations respecting the destruction
ofHerculaneum, Pompeii, and Stabiæ, filledthe minds of the
people with frightfulimages.
The hot steam which rose from thecrater during the eruption and passedinto the atmosphere, formed on cooling athick mass of clouds, around the columnof ashes and fire, 9000 feet in height.This sudden condensation of steam, and,as Gay-Lussac has shown, the very for-mation of the clouds, increases the elec-tric tension. Lightnings burst forth in alldirections from the column of ashes, andthe rolling thunder might clearly be dis-tinguished from the interior noise of thevolcano. At no former eruption had theplay of electric charges been so sur-prising.
On the morning of the 26th of Octo-ber, a singular account was
circulated,that a current of boiling water had issuedfrom the
crater, and rushed down fromthe cone of ashes. Monticelli, the
zea-lous and learned observer of the volca-no, soon discerned that
the rumour hadbeen occasioned by an optical deception.The supposed
current of water wasnothing but a dry mass of ashes, whichflowed
down, like quicksand, from a fis-sure in the superior edge of the
crater.A drought, which had completely desolat-ed the fields,
preceded the eruption, butthe volcanic thunderstorm
occasioned,towards its termination, a very heavyand continued
rain. Such a phenomenoncharacterizes the conclusion of an
erup-tion in every zone. On account of thecone of ashes being
generally coveredwith clouds during this time, and likewisebecause
the torrents of rain are heaviestin its neighbourhood, currents of
mudflow down on all sides. The affrightedpeasant considers it to
be water whichhas risen from the interior of the crater,and the
deceived geognost conceives thathe recognises in it either sea-water,
ormud-like volcanic productions, which arecalled eruptions boueses, or, as the oldFrench
systematic writers termed them,products of a fiery-aqueous
liquefaction.
|253|
|Spaltenumbruch|
When the summits of volcanoes (as isgenerally the case in the chain of
the An-des,) extend into the region of eternalsnow, or even to
double the height ofÆtna, the melted snow renders the
in-undations amazingly frequent and destruc-tive. They are
phenomena meteorologi-cally connected with volcanic eruptions,and
are multifariously modified by thealtitude of the mountains, the extent
oftheir summits covered with eternal snow,and the calefaction of
the sides of the coneof ashes; but they should never be
con-sidered as real volcanic phenomena.Subterranean lakes, in
connexion withalpine rivers, are formed both on theslopes and at
the foot of the mountains.When the earthquakes which precedeevery
eruption in the chain of the Andes,shake with mighty force the entire
massof the volcano, the subterranean vaultsare opened, and emit,
at the same time,water, fishes, and tufa-mud. This is thesingular
phenomenon that furnishes the
pimelodes cyclopum, which the inhabitantsof the
high lands of Quito call prenadilla,
and which was described by me soon af-ter my return. When the
summit of themountain Carguairazo, to the north of|Spaltenumbruch|Chimborazo,
and 18,000 feet high, fell,in the night between the 19 and 20th
ofJune, 1698, the surrounding fields, to theextent of about 43
English square miles,were covered with mud and fishes. Thefever
which raged in the town of Ibarra,seven years before, had been ascribed
toa simular eruption of fishes from the vol-cano Imbaburu. I recur
to these facts,because they throw some light on the dif-ference
between the eruption of ashes,and that of mud-like masses of tufa
andtrass, which contain wood, coal, andshells.
The quantity of ashes ejected by Ve-suvius in the late eruptions like all otherthings which are connected with great andappalling phenomena, has been enor-mously exaggerated in the public papers;and two Neapolitan chemists, VincenzoPepe, and Giuseppe di Nobili, have af-firmed, that they contain gold and silver,notwithstanding the contradiction of Mon-ticelli and Covelli. According to my ex-amination, the stratum of ashes which hadfallen in twelve days, towards Bosche treCase, on the slope of the cone, whererapilli were mixed with it, was only threefeet in thickness, and in the plain, it didnot exceed from 15 to 18 inches. Mea-surements of this kind must not be madein places where the ashes have beendrifted by wind, like snow, or sand, norin those where they have been accumu-lated by water. The times are pastin which we sought only for the marvel-lous in volcanic phenomena, and, likeCtesias, made the ashes of Ætna fly to theIndian peninsula. Some of the Mexicangold and silver mines are certainly intrachytic porphyry, but in the ashes ofVesuvius which I collected, and which,at my desire, have been analyzed byHenry Rose, of Berlin, an excellent che-mist, no traces of either metal could bediscovered.
However great may be the discrepan-cy between the results that I have
heregiven, but which agree with Monticelli’smore exact
observations, and thosewhich have been circulated during sever-al
months past, yet the eruption of ashesfrom Vesuvius, from the 24th to
the 28thof October, still remains the most re-markable of which we
have any certainaccount since the death of the elderPliny. Its
quantity perhaps was threetimes as great as that of all the
ashes,collectively, which have been observedto fall, during the
time in which volcanicphenomena have been attentively con-sidered.
A stratum of from 15 to 18 in-ches in thickness, seems at first
viewunimportant, if compared to the masswith which we find Pompeii
to be cover-ed; but without speaking of the torrentsand
inundations which certainly mayhave increased this mass for
centuries,without renewing the violent disputeconcerning the cause
of the destructionof the Campanian towns, which have beencarried
on with so much skepticism onthe other side of the Alps, it may be
af-firmed that the eruptions of one andthe same volcano at distant
periods canby no means be compared with respectto their intensity.
All conclusions found-ed on analogy are insufficient, when
thequestion is about quantitative propor-tions,—the
quantity of ashes and lava, theheight of the column of smoke, or
theviolence of the detonation.
From the geographical description ofStrabo, and from an opinion of Vitruviusconcerning the volcanic origin of pumice,we see that until the year in which Ves-pasian died, that is to say, until the erup-tion which overwhelmed Pompeii, Ve-suvius was more like an extinguishedvolcane than a solfataro.
When after long rest the subterraneanpowers suddenly open new passages,
andagain break through beds of primitiverocks and of trachyte,
effects mustnecessarily take place, for which all thephenomena
subsequently observed donot afford any standard of comparison.|254|It may be clearly seen from the well-known
letter in which the younger Plinyannounces the death of his uncle to
Ta-citus, that the recommencement of theeruptions, I might say,
the awakening ofthe dormant volcano, began with aneruption of
ashes. The same circum-stance was observed at Xorullo, in
Sept.1759, when the new volcano, breakingthrough beds of syenite
and trachyte,suddenly arose in the plain. The pea-sants fled,
because they found in theirhuts, ashes that had been ejected
fromthe fissures of the earth, which was burstin every place.
Every partial eruption,in the periodical general eruptions
ofvolcanoes, terminates with a shower ofashes.
There is a passage in Pliny’s letter,which shows, that the dry
ashes whichhad fallen from the air had already at-tained a height
of from four to five feet,in the commencement of the eruption,and
without the effect of accumulation bywater. “The court which led
to his[uncle’s] apartment,” he says,
“beingnow almost filled with ashes and pumice,would have
been impossible for him, ifhe had continued there any longer,
tohave made his way out.” In the narrowspace of a court,
the wind could nothave had any great effect in accumulat-ing the
ashes.
I have ventured to interrupt my com-parative view of volcanoes by observa-tions solely on Vesuvius, partly on ac-count of the great interest which the lasteruption has excited, and partly becauseevery great fall of ashes almost involun-tarily reminds us of the classic ground ofPompeii and Herculaneum. We havehitherto considered the form and the ef-fects of those volcanoes which are inpermanent communication with the in-terior of the earth, by means of a craterTheir summits are raised masses of tra-chyte and lava, intersected by numerousveins; the duration of their effectscauses us to believe that they have avery stable and undisturbed structure.They posess, I may say, a more indivi-dual character, which remains the sameduring long periods. Neighbouringmountains often furnish completely dif-ferent products, leucite-lava, and felspar-lava; obsidian, with pumice, and basalticmasses containing olivine. They belongto the newer phenomena of the earth,pass generally through all the strata ofsecondary rocks, and their eruptions andcurrents of lava are of later origin thanour valleys. Their life, if I may usethat expression, depends upon the man-ner and duration of their connexion withthe interior of the earth. They oftenrest for centuries, suddenly take fireagain, and terminate as solfataras, whichemit steam, gases, and acids. Some-times, as on the Peak of Teneriffe, theirsummit has already become such a de-pository of reproduced sulphur, whilemighty currents of lava flow from thesides of the mountain, like the basalt be-low, and above, where the pressure isless, like obsidian with pumice.
|261|
Independently of these with perma-nent craters, volcanic phenomena
ofanother kind exist, which have been ob-served less frequently,
but are princi-pally interesting in geognosy, and remindus of the
primitive world; that is to say,of the earliest revolutions of our
earth.Mountains of trachyte suddenly open, ejectlava and ashes,
and close again, perhaps,for ever; thus was it with the mighty
An-tisana; and thus with the Epomæus, in Is-chia, in 1302.
Such an eruption sometimestakes place even in the plain as in the
highlands of Quito; in Iceland, far fromHecla; and in
Eubœa, in the Lelanticfields. Many of the islands which
havebeen raised up are owing to these tem-porary phenomena. In
these cases thecommunication with the interior of theearth is not
permanent, and the effectceases as soon as the fissure, which is
thecommunicating channel, is closed again.The veins of basalt,
dolerite, and por-phyry, which, in different parts of theworld,
pass through every formation;and those of syenite,
augite-porphyry,and amygdaloid, which are characteristicof the
newest strata of the transition for-mation, and of the oldest rocks of
the se-condary strata, have probably been form-ed in a similar
manner. In the first ageof our planet, the yet liquid
substancespenetrated through the crust of the earth,which was
every where intersected byfissures, and assumed the form of
granu-lar rocks, either in veins, or spreadingover and expanding
themselves in strata.The rocks strictly volcanic which
theprimitive ages have afforded us, havenot flowed in currents
like the lava ofour insulated conical hills; the samemixture of
augite, titaniferous iron, glassyfelspar, and hornblende, may have
ex-isted at different periods, but at one timeit may have
approached nearer to basalt,and at others to trachyte; the
chemicalsubstances may have combined in a crys-talline form, in
distinct proportions, aswe are taught by M. Mitscherlich’s
newand important labours, and by the analo-gy of artificial
products of fire: we findthat substances similarly formed have
ar-rived at the surface of the earth in verydifferent ways; they
have either been|262|
|Spaltenumbruch|merely raised, or protruded by tempo-rary fissures through the
older strata;that is to say, through the already oxi-dized surface
of the earth; or they haveflowed, as currents of lava, from
conicalhills with a permanent crater. By con-founding such
different phenomena toge-ther, the geognosy of volcanoes is
carriedback to that darkness from which a greatnumber of
comparative observations arebeginning to extricate it.
The question has often been asked,What is it that burns in volcanoes?What was it that excited the heat bywhich earths and metals were melted?Modern chemistry answers, that the sub-stances which melt are the metals of theearths and alkalies. The solid crust ofthe earth, already oxidized, separatedthe surrounding air with its oxygen, fromthe combustible unoxidized substancesof the interior of our planet. The ob-servations which have been made inmines and caves in every zone, andwhich, in conjunction with M. Arago, Ihave collected in a particular paper, de-monstrate that the heat of the mass of theearth is yet much greater than the meantemperature of the atmosphere at thesame place. Such a remarkable and al-most generally proved fact, is closelyconnected with those which are provedby volcanic phenomena. Laplace haseven gone so far as to endeavour to cal-culate the depth at which the body ofthe earth may be considered to be a melt-ed mass. Whatever doubts may be en-tertained, notwithstanding the venerationdue to so great a name, with respect tothe numerical certainty of such a calcu-lation, thus much remains probable; thatall volcanic phenomena originate in avery simple cause, in a permanent or ina variable communication between theinterior and the exterior of our planet.
The pressure of elastic vapour forcesthe melted substances upwards throughdeep fissures while they are undergoingoxidation; volcanoes, if I may so speak,are intermitting springs of the earth; theliquid mixtures of metals, alkalies, andearths, which on cooling become currentsof lava, flow quietly when they are rais-ed, and find a vent. The ancients ima-gined, according to Plato’s Phædon, thatall volcanic currents of fire flowed in asimilar way, from the Periphlegeton.
It may be permitted me, perhaps, toadd to these considerations one which isstill more hazardous. In this interiorheat of the earth, indicated by experi-ments with the thermometer, and by ob-servations on volcanoes, the cause, per-haps, may be found, of one of the mostwonderful phenomena which the exami-nation of fossils presents to us. Tropi-cal forms of animals, arboriform ferns,palms, and bamboo-like plants, lie inter-red in the cold north. The primitiveworld every where shows a distributionof organic forms at variance with thethen existing nature of the climate. Inorder to solve this important problem,several hypotheses have been invented;as the neighbourhood of a comet, thealtered inclination of the ecliptic, the in-creased intensity of the solar light. Nei-ther of these has been sufficient to satisfyat once the astronomer, the natural phi-losopher, and the geognost. For mypart, I leave the axis of the earth unal-tered, as well as the light of the solardisc, by the spots on which, a celebratedastronomer has explained both the fertili-ty and the unfruitfulness of the fields;but I believe, that in every planet, inde-pendently of its relation to a central body,and of its astronomical situation, variouscauses exist of the production of heat;oxidation, precipitation, and a change inthe capacity of bodies; by increase ofelectromagnetic charge, by the openingof a communication between the interiorand the exterior part of the earth.
Where the deeply cleft crust of theearth in the primitive world
radiatedheat from its fissures, whole countries,|Spaltenumbruch|perhaps,
could produce for centuries,palms and aborescent ferns, and
sustainall the animals of the torrid zone. Ac-cording to this
view, to which I have al-ready alluded in a work just
published,“Essai Géognostique sur le Gissementdes Roches
dans les deux Hemispheres,”the temperature of volcanoes would
bethat of the interior of the earth itself, andthe same cause
which now occasions suchdreadful destruction, would once
haveoccasioned, on the newly oxidated crustof the earth, upon the
deeply cleft strataof rocks, the most luxuriant growth ofplants in
every zone.
Even if any one should be inclined tosuppose, in order to explain the marvel-lous distribution of tropical forms in theirancient graves, that shaggy animals of theelephant tribe now imbedded in icebergs,were once peculiar to a northern cli-mate, and that similar forms belonging tothe same primary types, like lions andlynxes, could live in very different climates,such an explanation could not, however,be extended to the products of vegeta-tion. For reasons which the physiologyof plants explains, palms, and arboriformmonocoty ledones cannot sustain thenorthern cold, and in the geological pro-blem we here speak of, it seems difficultto me to separate plants and animals.The same explanation must be applied toboth.
Towards the end of this paper, I havecombined uncertain hypothetical suppo-sitions with facts collected from the mostdifferent parts of the world. The philo-sophical knowledge of nature rises abovea mere description of nature. It doesnot consist in a sterile aggregation of iso-lated observations. It may sometimes beallowed, therefore, to the curious andever-active mind of man, to look backupon the past, to imagine what cannotbe clearly known, and to amuse himselfwith the ancient, and, under many forms,returning mysteries of geogony.
On the Constitution and Mode of Action ofVolcanoes, in different Parts of theEarth. By Alexander Von Humboldt.Read before the Royal Academy of Sciences of Berlin,Jan. 24, 1823.
No. I.
On the Constitution and Mode of Action ofVolcanoes, in different Parts of theEarth. By Alexander Von Humboldt.Read before the Royal Academy of Sciences of Berlin,Jan. 24. 1823.
No. II.
On the Constitution and Mode of Action ofVolcanoes, in different Parts of theEarth. By Alexander Von Humboldt.Read before the Royal Academy of Sciences of Berlin.Jan. 24. 1823.
No. III.
On the Constitution and Mode of Action ofVolcanoes, in different Parts of theEarth. By Alexander Von Humboldt.Read before the Royal Academy of Sciences of Berlin.Jan. 24. 1823.
No. IV.
On the Constitution and Mode of Action ofVolcanoes, in different Parts of theEarth. By Alexander Von Humboldt.Read before the Royal Academy of Sciences of Berlin.Jan. 24. 1823.
No. V.