Transcriber Note
Text emphasis denoted as _Italics_.
THE
International Scientific Series
VOL. XXXV.
_Frontispiece._
[Illustration]
Sections of Igneous Rocks, illustrating the passage from the glassy to
the crystalline structure.
1. Vitreous Rock. 2. Semi-Vitreous Rock. 3. Vitreous Rock with
Sphærulites. 4. Rock with Crypto-crystalline Base. 5. Rock with
Micro-crystalline Base. 6. Rock of Granite Structure built up
entirely of Crystals.
[_See pp._ 63-68.
VOLCANOES
WHAT THEY ARE and WHAT THEY TEACH
BY
JOHN W. JUDD, F.R.S.
PROFESSOR OF GEOLOGY IN THE ROYAL SCHOOL OF MINES
_WITH 96 ILLUSTRATIONS_
SIXTH EDITION
LONDON
KEGAN PAUL, TRENCH, TRÜBNER & CO. Ltd.
PATERNOSTER HOUSE, CHARING CROSS ROAD
1903
(_The rights of translation and of reproduction are reserved._)
PREFACE.
In preparing this work, I have aimed at carrying out a design suggested
to me by the late Mr. Poulett Scrope, the accomplishment of which has
been unfortunately delayed, longer than I could have wished, by many
pressing duties.
Mr. Scrope's well-known works, 'Volcanoes' and 'The Geology and Extinct
Volcanoes of Central France'--which passed through several editions
in this country, and have been translated into the principal European
languages--embody the results of much careful observation and acute
reasoning upon the questions which the author made the study of his
life. In the first of these works the phenomena of volcanic activity
are described, and its causes discussed; in the second it is shown that
much insight concerning these problems may be obtained by a study of
the ruined and denuded relics of the volcanoes of former geological
periods. The appearance of these works, in the years 1825 and 1827
respectively, did much to prepare the minds of the earlier cultivators
of science for the reception of those doctrines of geological
uniformity and continuity, which were shortly afterwards so ably
advocated by Lyell in his 'Principles of Geology.'
Since the date of the appearance of the last editions of Scrope's
works, inquiry and speculation concerning the nature and origin of
volcanoes have been alike active, and many of the problems which were
discussed by him, now present themselves under aspects entirely new and
different from those in which he was accustomed to regard them. No one
was ever more ready to welcome original views or to submit to having
long-cherished principles exposed to the ordeal of free criticism than
was Scrope; and few men retained to so advanced an age the power of
subjecting novel theories to the test of a rigorous comparison with
ascertained facts.
But this eminent geologist was not content with the devotion of his
own time and energies to the advancement of his favourite science, for
as increasing age and growing infirmities rendered travel and personal
research impossible, he found a new source of pleasure in seeking
out the younger workers in those fields of inquiry which he had so
long and successfully cultivated, and in furthering their efforts by
his judicious advice and kindly aid. Among the chosen disciples of
this distinguished man, who will ever be regarded as one of the chief
pioneers of geological thought, I had the good fortune to be numbered,
and when he committed to me the task of preparing a popular exposition
of the present condition of our knowledge on volcanoes, I felt that I
had been greatly honoured.
In order to keep the work within the prescribed limits, and to avoid
unnecessary repetitions, I have confined myself to the examination of
such selected examples of volcanoes as could be shown to be really
typical of all the various classes which exist upon the globe; and
I have endeavoured from the study of these to deduce those general
laws which appear to govern volcanic action. But it has, at the
same time, been my aim to approach the question from a somewhat new
standpoint, and to give an account of those investigations which have
in recent times thrown so much fresh light upon the whole problem.
In this way I have been led to dwell at some length upon subjects
which might not at first sight appear to be germane to the question
under discussion;--such as the characters of lavas revealed to us
by microscopic examination; the nature and movements of the liquids
enclosed in the crystals of igneous rocks; the relations of minerals
occurring in some volcanic products to those found in meteorites; the
nature and origin of the remarkable iron-masses found at Ovifak in
Greenland; and the indications which have been discovered of analogies
between the composition and dynamics of our earth and those of other
members of the family of worlds to which it belongs. While not evading
the discussion of theoretical questions, I have endeavoured to keep
such discussions in strict subordination to that presentation of the
results attained by observation and experiment, which constitutes the
principal object of the work.
The woodcuts which illustrate the volume are in some cases prepared
from photographs, and I am indebted to Mr. Cooper for the skill with
which he has carried out my wishes concerning their reproduction.
Others among the engravings are copies of sketches which I made in
Italy, Hungary, Bohemia, and other volcanic districts. The whole of the
wood-blocks employed by Mr. Poulett Scrope in his work on Volcanoes
were placed at my disposal before his death, and such of them as
were useful for my purpose I have freely employed. To Captain S. P.
Oliver, R.A., I am obliged for a beautiful drawing made in the Island
of Bourbon, and to Mr. Norman Lockyer and his publishers, Messrs.
Macmillan & Co., for the use of several wood-blocks illustrating
sun-spots and solar prominences.
J. W. J.
London: _May 1881_.
CONTENTS.
CHAPTER I.
PAGE
INTRODUCTORY: NATURE OF THE ENQUIRY
1
CHAPTER II.
THE NATURE OF VOLCANIC ACTION
7
CHAPTER III.
THE PRODUCTS OF VOLCANIC ACTION
39
CHAPTER IV.
THE DISTRIBUTION OF THE MATERIALS EJECTED FROM VOLCANIC VENTS
67
CHAPTER V.
THE INTERNAL STRUCTURE OF VOLCANIC MOUNTAINS
112
CHAPTER VI.
THE VARIOUS STRUCTURES BUILT UP AROUND VOLCANIC VENTS
161
CHAPTER VII.
THE SUCCESSION OF OPERATIONS TAKING PLACE AT VOLCANIC CENTRES
186
CHAPTER VIII.
THE DISTRIBUTION OF VOLCANOES UPON THE SURFACE OF THE GLOBE
224
CHAPTER IX.
VOLCANIC ACTION AT DIFFERENT PERIODS OF THE EARTH'S HISTORY
247
CHAPTER X.
THE PART PLAYED BY VOLCANOES IN THE ECONOMY OF NATURE
281
CHAPTER XI.
WHAT VOLCANOES TEACH US CONCERNING THE NATURE
OF THE EARTH'S INTERIOR
307
CHAPTER XII.
THE ATTEMPTS WHICH HAVE BEEN MADE TO EXPLAIN
THE CAUSES OF VOLCANIC ACTION
331
INDEX
371
ILLUSTRATIONS.
Sections of igneous rocks illustrating the passage from the
glassy to the crystalline structure
_Frontispiece_
Fig. Page
1. Stromboli, viewed from the north-west, April 1874 _to face p._ 10
2. Map of the Island of Stromboli 11
3. Section through the Island of Stromboli from north-west to
south-east 13
4. The crater of Stromboli as viewed from the side of the
Sciarra during an eruption on the morning of April 24,
1874. 14
5. Vesuvius in eruption, as seen from Naples, April 26, 1872.
(_From a photograph_) _to face p._ 24
6. View of Vulcano, with Vulcanello in the foreground--taken
from the south end of the Island of Lipari 43
7. Minute cavities, containing liquids, in the crystals of rocks.
(_After Zirkel_) _to face p._ 60
8. Minute liquid-cavity in a crystal, with a moving bubble.
(_After Hartley_) 63
9. Cavity in crystal, containing carbonic-acid gas at a
temperature of 86° F., and passing from the liquid to
the gaseous condition. (_After Hartley_) 64
10. Monte Nuovo (440 ft high) on the shores of the Bay of Naples.
(_After Scrope_) 76
11. Map of the district around Naples, showing Monte Nuovo and the
surrounding volcanoes of older date 78
12. Outlines of the summit of Vesuvius during the eruption of
1767. (_After Sir W. Hamilton_) _to face p._ 80
13. Crater of Vesuvius formed during the eruption of 1822
(_After Scrope_) 82
14. Crater of Vesuvius in 1756, from a drawing made on the spot.
(_After Sir W. Hamilton_) 84
15. The summit of Vesuvius in 1767, from an original drawing.
(_After Sir W, Hamilton_) 85
16. Summit of Vesuvius in 1843 86
17. Outlines of Vesuvius, showing its form at different periods
of its history 87
18. Cascade of lava tumbling over a cliff in the Island of
Bourbon. (_After Capt. S. P. Oliver, R.A._) 93
19. Lava-stream (obsidian) in the Island of Vulcano, showing
the imperfect liquidity of the mass 95
20. Interior of a rhyolitic lava-stream in the Island of Lipari,
showing broad, sigmoidal folds, produced by the slow
movements of the mass 96
21. Interior of a rhyolitic lava-stream in the Island of Lipari,
showing the complicated crumplings and puckerings,
produced by the slow movements of the mass 96
22. Vesuvian lava-stream of 1858, exhibiting the peculiar
'ropy' surfaces of slowly-moving currents.
(_From a photograph_) _to face p._ 98
23. Vesuvian lava-stream of 1872, exhibiting the rough cindery
surfaces characteristic of rapidly flowing currents.
(_From a photograph_) _to face p._ 96
24. Concentric folds on mass of cooled lava. (_After Heaphy_) 100
25. Mass of cooled lava formed over a spiracle on the slopes
of Hawaii. (_After Dana_) 100
26. Group of small cones thrown up on the Vesuvian lava-current
of 1855. (_After Schmidt_) 101
27. Natural section of a lava-stream in the Island of Vulcano,
showing the compact central portion and the scoriaceous
upper and under surfaces 104
28. Section of a lava-stream exposed on the side of the river
Ardèche, in the south-west of France. (_After Scrope_) 106
29. Portion of a basaltic column from the Giant's Causeway,
exhibiting both the ball-and-socket and the
tenon-and-mortise structure 107
30. Vein of green pitchstone at Chiaja di Luna, in the Island
of Ponza, breaking up into regular columns and into
spherical masses with a concentric series of joints.
(_After Scrope_) 108
31. Illustration of the 'perlitic structure' in glassy rocks 109
32. Transverse section of a lava-stream 111
33. The Kammerbühl, or Kammerberg, Bohemia (as seen from
the south-west) 113
34. Section of the Kammerbühl in Bohemia 114
35. Natural section of a volcanic cone in the Island of Vulcano 116
36. Section in the side of the Kammerbühl, Bohemia 118
37. Experimental illustration of the mode of formation of
volcanic cones, composed of fragmental materials 120
38. Natural section of a tuff-cone, forming the Cape of Misenum,
and exhibiting the peculiar internal arrangement,
characteristic of volcanoes composed of fragmentary
materials. (_After Scrope_) 121
39. Section of a small scoria-cone formed within the crater of
Vesuvius in the year 1835, illustrating the filling up of
the central vent of the cone by subsequent ejections.
(_After Abich_) 122
40. Volcanic cones composed of scoriæ, and breached on one
side by the outflow of lava-currents. (_After Scrope_) 128
41. Campo Bianco, in the Island of Lipari. A pumice-cone
breached by the outflow of an obsidian lava-stream
_to face p._ 124
42. Volcanic cones in Auvergne, which have suffered to some
extent from atmospheric denudation. (_After Scrope_) 124
43. Experimental illustration of the mode of formation of
volcanic cones composed of viscid lavas. (_After Reyer_) 126
44. The Grand Puy of Sarcoui, composed of trachyte, rising
between two breached scoria-cones (Auvergne). (_After
Scrope_) 126
45. Volcanic cone (Mamelon) composed of very viscid lava
(Island of Bourbon). (_After Bory de St. Vincent_) 127
46. Another Mamelon in the Island of Bourbon, with a crater
at its summit. (_After Bory de St. Vincent_) 127
47. Cliff-section in the Island of Madeira, showing how a
composite volcano is built up of lava-streams, beds of
scoriæ, and dykes. (_After Lyell_) 125
48. Section seen at the cascade, Bains du Mont Dore. (_After
Scrope_) 130
49. Section in the Island of Ventotienne, showing a great
stream of andesitic lava overlying stratified tuffs.
(_After Scrope_) 130
50. Cliff on the south side of the Island of San Stephano 131
51. The headland of Monte della Guardia, in the Island of Ponza 131
52. Western side of the same headland, as seen from the north
side of Luna Bay 132
53. Sea-cliff at Il Capo, the north-east point of Salina,
showing stratified agglomerates traversed by numerous
dykes, the whole being unconformably overlaid by
stratified, aqueous deposits 137
54. Section observed in the Val del Bove, Etna, showing a
basaltic dyke, from the upper part of which a
lava-current has flowed 138
55. Basaltic dykes projecting from masses of stratified scoriæ
in the sides of the Val del Bove, Etna 134
56. Sheets of igneous rock (basalt) intruded between beds of
sandstone, clay, and limestone (Island of Skye) 137
57. Plan of the dissected volcano of Mull in the Inner
Hebrides _to face p._ 142
58. Section of the volcano of Mull along the line A B " 142
59. Summit of the volcano of Monte Sant' Angelo, in Lipari,
exhibiting a crater with walls worn down by denudation 158
60. Outlines of lava-cones 160
61. Diagram illustrating the formation of parasitic cones along
lines of fissure formed on the flanks of a great volcanic
mountain 162
62. Outline of Etna, as seen from Catania 162
63. Outline of Etna, as seen from the Val del Bronte 163
64. Plan of the volcano forming the Island of Ischia 163
65. A primary parasitic cone, with a secondary one at its
base--Ischia 164
66. Scoria-cone near Auckland, New Zealand, with a lava-current
flowing from it. (_After Heaphy_) 165
67. Section of rocks below the ancient triassic volcano of
Predazzo in the Tyrol 165
68. Cotopaxi, as seen from a distance of ninety miles. (_After
Humboldt_) 168
69. Citlaltepetl, or the Pic d'Orizaba, in Mexico, as seen from
the Forest of Xalapa. (_After Humboldt_) 169
70. Lac Paven, in the Auvergne. (_After Scrope_) 171
71. The crater-lake called Lago del Bagno, in Ischia, converted
into a harbour 172
72. Lake of Gustavila, in Mexico. (_After Humboldt_) 172
73. Peak of Teneriffe, surrounded by great crater-rings. (_After
Piazzi-Smyth_) 175
74. The volcano of Bourbon, rising in the midst of a crater-ring
four miles in diameter. (_After Bory de St. Vincent_) 176
75. The volcano of Bourbon, as seen from another point of
view, with three concentric crater-rings encircling its
base. (_After Bory de St. Vincent_) 176
76. Vesuvius as seen from Sorrento, half encircled by the
crater-ring of Somma 177
77. Outlines of various volcanoes illustrating the different
relations of the craters to cones _to face p._ 178
78. Island thrown up In the Mediterranean Sea in July and
August, 1831. (_After the Prince de Joinville_) 179
79. Sinter-cones surrounding the orifices of geysers 183
80. Diagram illustrating the mode of formation of travertine-
and sinter-terraces on the sides of a hill of tuff 185
81. Map of the volcanic group of the Lipari Islands, illustrating
the position of the lines of fissure upon which
the volcanoes have been built up 192
82. The Puy de Pariou, in the Auvergne, illustrating the shifting
of eruption along a line of fissures 193
83. Ideal section of the Puy de Pariou 194
84. Fissure formed on the flanks of Etna during the emotion
of 1865. (_After Silvestri_) 194
85. Plan of the Island of Vulcano, based on the map of the
Italian Government 196
86. Vulcanello, with its three craters 197
87. Section of basalt from Ovifak, Greenland, with particles of
metallic iron diffused through its mass 319
88. Diagram illustrating the relations between the terrestrial
and the extra-terrestrial rocks _to face p._ 322
89. A group of sun-spots. (_After Secchi_) 362
90. A sun-spot, showing the great masses of incandescent
vapour rising or falling within it. (_After Secchi_) 363
91. The edge of a sun-spot, showing a portion of the prominent
masses of incandescent gas (A) which detached itself
at B and floated into the midst of the cavity.
(_After Norman Lockyer_) 363
92. Drawing of a solar prominence made by Mr. Norman
Lockyer, March 14, 1869, at 11 h. 5 m. A.M. 364
93. The same object, as seen at 11 h. 15 m. on the same day.
(_After Norman Lockyer_) 365
94. Drawings of a solar prominence at four different periods
on September 7, 1871. (_After Young_) 366
95. A group of Lunar craters (Maurolycus, Barocius, &c.), the
largest being more than sixty miles in diameter 368
VOLCANOES.
CHAPTER I.
INTRODUCTORY: NATURE OF THE INQUIRY.
'What is a volcano?' This is a familiar question, often addressed to us
in our youth, which 'Catechisms of Universal Knowledge,' and similar
school manuals, have taught us to reply to in some such terms as the
following: 'A volcano is a burning mountain, from the summit of which
issue smoke and flames.' Such a statement as this, it is probable, does
not unfairly represent the ideas which are, even at the present day,
popularly entertained upon the subject.
But in this, as in so many other cases, our first step towards the
acquirement of scientific or exact knowledge, must be the unlearning of
what we have before been led to regard as true. The description which
we have quoted is not merely incomplete and inadequate as a whole,
but each individual proposition of which it is made up is grossly
inaccurate, and, what is worse, perversely misleading. In the first
place, the action which takes place at volcanoes is not 'burning,' or
combustion, and bears, indeed, no relation whatever to that well-known
process. Nor are volcanoes necessarily 'mountains' at all; essentially,
they are just the reverse--namely, holes in the earth's crust, or
outer portion, by means of which a communication is kept up between
the surface and the interior of our globe. When mountains do exist at
centres of volcanic activity, they are simply the heaps of materials
thrown out of these holes, and must therefore be regarded not as the
causes but as the consequences of the volcanic action. Neither does
this action always take place at the 'summits' of volcanic mountains,
when such exist, for eruptions occur quite as frequently on their sides
or at their base. That, too, which popular fancy regards as 'smoke'
is really condensing steam or watery vapour, and the supposed raging
'flames' are nothing more than the glowing light of a mass of molten
material reflected from these vapour clouds.
It is not difficult to understand how these false notions on the
subject of volcanic action have come to be so generally prevalent.
In the earlier stages of its development, the human mind is much
more congenially employed in drinking in that which is marvellous
than in searching for that which is true. It must be admitted, too,
that the grand and striking phenomena displayed by volcanoes are
especially calculated to inspire terror and to excite superstition,
and such feelings most operate in preventing those close and accurate
observations which alone can form the basis of scientific reasoning.
[Sidenote: IDEAS OF THE ANCIENTS.]
The ancients were acquainted only with the four or five active
volcanoes in the Mediterranean area; the term 'volcano' being the
name of one of these (Vulcano, or Volcano, in the Lipari Islands),
which has come to be applied to all similar phenomena. It is only in
comparatively modern times that it has become a known £act that many
hundreds of volcanoes exist upon the globe, and are scattered over
almost every part of its surface. Classical mythology appropriated
Vulcano as the forge of Hephæstus, and his Roman representative Vulcan,
while Etna was regarded as formed by the mountains under which a
vengeful deity had buried the rebellious Typhon; it may be imagined,
therefore, that any endeavour to more closely investigate the phenomena
displayed at these localities would be regarded, not simply as an act
of temerity, but as one of actual impiety. In mediæval times similar
feelings would operate with not less force in the same direction, for
the popular belief identified the subterranean fires with a place of
everlasting torment; Vulcano was regarded as the place of punishment
of the Arian Emperor Theodosius, while Etna was assigned to poor Anne
Boleyn, the perverter of faith in the person of its stoutest defender.
That such feelings of superstitious terror in connection with volcanoes
are, even at the present day, far from being extinct, will be attested
by every traveller who, in carrying on investigations about volcanic
centres, has had to avail himself of the assistance of guides and
attendants from among the common people.
Among the great writers of antiquity we find several who had so far
emancipated their minds from the popular superstitions as to be able
to enunciate just and rational views upon the subject of volcanoes.
Until quite recent times, however, their teaching was quite forgotten
or neglected, and the modern science of Vulcanology may be said to have
entirely grown up within the last one hundred years.
The great pioneer in this important branch of research was the
illustrious Italian naturalist Spallanzani, who, in the year 1788,
visited the several volcanoes of his native land, and published an
account of the numerous valuable and original observations which he
had made upon them. About the same time the French geologist Dolomieu
showed how much light might be thrown on the nature of volcanic action
by a study of the various materials which are ejected from volcanic
vents; while our own countryman. Sir William Hamilton, was engaged in
a systematic study of the changes in form of volcanic mountains, and
of the causes which determine their growth. At a somewhat later date
the three German naturalists. Von Buch, Humboldt, and Abich, greatly
extended our knowledge of volcanoes by their travels in different
portions of the globe.
[Sidenote: CHARACTER OF MODERN RESEARCHES.]
The first attempt, however, to frame a satisfactory theory of volcanic
action, and to show the part which volcanoes have played in the past
history of our globe, together with their place in its present economy,
was made in 1825, by Poulett Scrope, whose great work, 'Considerations
on Volcanoes,' may be regarded as the earliest systematic treatise on
Vulcanology. Since the publication of this work, many new lines of
inquiry have been opened up in connection with the subject, and fresh
methods of research have been devised and applied to it. More exact
observations of travellers over wider areas have greatly multiplied
the facts upon which we may reason and speculate, and many erroneous
hypotheses which had grown up in connection with the subject have been
removed by patient and critical inquiry.
We propose in the following pages to give an outline of the present
state of knowledge upon the subject, and to indicate the bearings
of those conclusions which have already been arrived at, upon the
great questions of the history of our globe and the relations which
it bears to the other portions of the universe. In attempting this
task we cannot do better than take up the several lines of inquiry
in the order in which they have been seized upon and worked out by
the original investigators; for never, perhaps, is the development
of thought in the individual mind so natural in its methods, and so
permanent in its effects, as when it obeys those laws which determined
its growth in the collective mind of the race. In our minds, as in our
bodies, development in the individual is an epitome, or microcosmic
reproduction, of evolution in the species.