Volcanoes of North America, etc

Front matter

VOLCANOES OF NORTH AMERICA VOLCANOES OF NORTH AMERICA. PLATS 1. Sketch map ol the world drawing general distribution of volcanoes. (Alter Jbgeph I'rc-siwich.) (Volcanoes cf North America shown on Plate i.) VOLCANOES OF NOETH AMERICA A READING LESSON FOR STUDENTS OF GEOGRAPHY AND GEOLOGY BY ISRAEL C. RUSSELL PROFESSOR OF GEOLOGY, UNIVERSITY OF MICHIGAN AUTHOR OF " LAKES OF NORTH AMERICA," "GLACIERS OF NORTH AMERICA," ETC. THE MACMILLAN COMPANY LONDON: MACMILLAN & CO., Ltd. 1897 All rights reserved Copyright, 1897, By THE MACMILLAN COMPANY. NottoooB IStfBB J. S. Cushing & Co. — Berwick & Smith Norwood Mass. U.S.A. V

Introduction

In the present volume the Western Hemisphere is considered as being divided into two portions ; namely, North and South America. Central America is included in the northern division for the reason that the student of volcanic phenomena finds a break in the volcanic belts which follow the western borders of the two con tinents, at the Isthmus of Darien. The series of active and recently extinct volcanoes forming the major part of the Windward islands, sepa rating the Caribbean Sea from the Atlantic, will not be considered, as it is most intimately associated with the geography and geology of South America. Although Iceland is more closely connected geographically with America than with Europe, its political association with the Old World, and the fact that it has frequently been described by European travellers, make it convenient to omit it from the present discussion.

Among the leading physical features of the southern prolongation of the North American continent compris ing Mexico and the Central American republics, are numerous still steaming and recently extinct volcanoes, some of which have had their birth since the Spanish conquest. This region also furnishes examples of violent volcanic eruptions, one of which is probably second, in VI

INTRODUCTION.

reference to intensity, among similar events witnessed by civilized man. Many phases of volcanic phenomena occur in the west ern portion of the United States. The lofty volcanic mountains of northern California, Oregon, and Washington are among the most beautiful examples of their class to be found in the world. To the eastward of these giant peaks, whose fiery glow has been replaced by the sheen of snow-fields and glaciers, lies a vast lava-covered re gion, the only known parallel of which, in the extent and thickness of the once molten rocks, occurs in north western India. In Alaska volcanic energy is still active, and more than a score of volcanoes have been in eruption since the voyages of Bering in 1725-30. It is the character and history of this vast volcanic belt, reaching from the tropical shores of Costa Rica to the western extremity of the bleak and inhospitable Aleu tian islands, that the attention of students of geology and geography is here invited.

The object of this book is to make clear the princi pal features of volcanoes in general, and to place in the hands of students a concise account of the leading facts thus far discovered, concerning the physical features of North America which can be traced directly to the in fluence of volcanic action. It is hoped that the accounts of volcanic eruptions here brought together and the discussions of the accompanying topographic changes, will lead the reader to con sult some of the numerous books to which reference is

INTRODUCTION.

VII made, and thus obtain, in many instances, more detailed information than it is practicable to include in a book of the character of the one here presented. While the facts described and discussed in the following pages were derived in many instances from personal observation, much is of necessity compiled from the writings of others. In all cases, I think, acknowledgments are 7 O made of the sources from which information has been borrowed. The numerous foot-notes inserted will ena ble the reader to verify the accuracy of those portions of the book which are essentially compilations. ISRAEL C. RUSSELL. University of Michigan, May 25, 1897. CONTENTS PAGE

INTRODUCTION.

v-vii

Chapter I Characteristics Of Volcanoes

Typf.s of Volcanoes : Stromboli ; Vesuvius ; Krakatoa ; Hawaiian islands ; fissure eruptions ; Deccan trap ; Columbia lava ; trap rocks of the Newark system 1-45 Stages in the Lives of Volcanoes 45-48 Characteristics of the Products of Volcanoes : Gaseous and sublimed products ; liquid and solid products ; lava streams ; tunnels in lava; aa; pahoehoe; scoriaceous surfaces of lava streams; characteristics of the bottoms of lava streams ; crystalline structure of the central portions of lava sheets ; fragmental products ; driblet cones ; Pele's hair ; bombs ; scoria cones ; sheets of volcanic sand and dust 48-80 Profiles of Volcanic Mountains 80-83 Structurf. of Volcanic Mountains: Cones formed of projectiles; composite cones ; dikes ; volcanic necks 83-90 Erosion of Volcanic Mountains 90-94 Subterranean Intrusions : Dikes ; sheets ; plugs ; laccolites ; subtuberant mountains ; generalizations 94-106 Characteristics of Igneous Rocks : Classification of igneous rocks based on physical characters, — on chemical characters, — on mineralogical characters ; granite ; basalt ; rhyolite ; trachyte ; andesite ; summary 106-126

Chapter II

General Distribution of the Active and Recently Extinct Volcanoes of North America 127-133 X CONTENTS PAGE

Chapter III

Volcanoes of Central America: General geology; Panama; list of Central American volcanoes 134-lo9 Young Volcanoes : Izalco ; birth of a volcano in Lake Ilopango ; a nameless volcano in Nicaragua ; Jorullo, Mexico . . 139-156 Older Volcanoes: Conseguina; Volcan del Fuego; Volcan de Agua 156-171

Chapter IV

Volcanoes of Mexico : Orizaba ; Popocatepetl ; Ixtaccihuatl ; Xinantecatl ; Tuxtla ; Cofre de Perote ; Colima ; volcanoes of northern Mexico ; volcanoes of Lower California 172-190

Chapter V

Volcanoes of the United States : San Francisco Mountain, Arizona ; Mt. Taylor, New Mexico ; Ice Spring craters, Utah ; Tabernacle crater, Utah; craters near Ragtown, Nevada; Mono valley, California; Mono craters; Mt. Shasta, California; Cinder cone, near Lassen's Peak, California ; Crater Lake, Oregon . . 191-233 The Great Volcanic Mountains of Oregon and Washington: Mt. Pitt ; Three Sisters and Mt. Jefferson ; Mt. Hood ; Mt. Adams ; Mt. St. Helen's ; Mt. Rainier (Tacoma) ; Mt. Baker . . 233-246 Cascade Mountains 246-250 Columbia Lava .......... 250-257 Volcanoes of the Coast Range 257 Volcanoes of the Rocky Mountain Region; Blackfoot basin, Idaho ; Colorado ; Spanish peaks ; New Mexico ; Canada . 257-267 Volcanoes of Alaska: The Aleutian volcanic belt; Cook's Inlet; Redoute ; St. Augustine ; Unimak Island ; Bogosloff Island ; Unalaska Island ; central and western Aleutian islands; summary, 267-283

Chapter VI

Deposits of Volcanic Dust : Distribution ; physical and chemical properties ; economic importance ....... 284-296 CONTENTS XI PAGE

Chapter VII

Theoretical Considerations : Interior heat of the earth ; physical conditions of the earth's interior; intrusive rocks; relation between intrusive rocks and volcanoes ; source of the steam of volcanoes; source of the heat of volcanoes ; source of the pressure which causes molten lava to rise in fissures in the earth's crust ; differences in lavas ; independence of neighboring volcanoes ; origin of fractures in the earth's crust; association of volcanoes with the sea; influence of water on volcanic eruptions . . . . 297-319 Other Hypotheses: Chemical hypothesis; mechanical hypothesis; steam hypotheses 319-324

Chapter VIII

Life History of a Volcano 327-338 INDEX ILLUSTRATIONS PLATES PLATE FACE PAGE 1. Sketch map of the world, showing distribution of volcanoes, Frontispiece 2. Vesuvius in eruption, 1S72 ........ 8 {a. Fusiyama, Japan ) J .... 82 b. St. Augustine, Cook's Inlet, Alaska, 1895 ) 4. Sketch map of North America, showing distribution of volcanoes, 128 5. Izalco, San Salvador, 1894 142 {a. Sau Francisco Mountain, Arizona ) .194 b. Volcanic neck near Mt. Taylor, New Mexico ) 7. Ice Spring craters, Utah 200 8. Map of Mono craters, California 216 9. Mt. Shasta, California 224 [a. General view of Cinder cone, near Lassen's Peak, California ) 10. \ l —8 ( b. Section of Cinder cone ' 11. Geological map of Cinder cone region, California .... 230 (a. Mt. Hood, Oregon ) „„„ { b. Crater of Mt. Hood ! [ a. Mt. St. Helen's, "Washington ) 23g 1 b. Mt. Rainier, Washington ' 14.

Mt. Rainier, Washington 244 (a. Pavloff volcano, Alaska | { b. Shishaldin volcano, Alaska ) s a. Bogosloff Island, Bering Sea j 280 ' 1 b. New Bogosloff ' ILLUSTRATIONS FIGURES FIGURE PAGE 1. Stromboli 4 2. Profiles of volcanic mountains ....... 81 3. Experiment illustrating the structure of a cinder cone ... 85 4. Ideal section through Vesuvius .87 5. Dike on the shore of Lake Superior 98 6. Sketch of Conseguina, Nicaragua 158 7. Map of a part of Paoha Island, Mono Lake, California . . . 213 8. Panum crater, Mono valley, California 222 9. Sections of small craters, Mono valley, California .... 223 10. Summit of Cinder cone, near Lassen's Peak, California . . 231 11. Volcanic dust as seen under the microscope

Chapter I Characteristics Of Volcanoes

Both the historical and scientific interest in volcanoes originated in southern Europe. Etna, Vesuvius, Santorin, and the volcanoes of the Lipari islands, figure in Greek and Roman mythology, and have made a deep impression on the history and poetry of the Mediterranean region. These same volcanoes, in later times, lead to a scientific study of the phenomena attending volcanic eruptions. Although the same phenomena that attracted the attention of philosophers to the volcanoes of southern Europe have been manifested at hundreds of other localities, and many times on a far grander scale than even Pompeii has witnessed, yet on account of the length of time that observations have been carried on in the region referred to, and the painstaking accuracy of much of the work done there, it will long remain classic ground to the student of nature, as well as to the historian, the poet, and the painter.

Types of Volcanoes In beginning the study of the volcanoes of North America, it is essential that we should learn at least the principal results attained in other regions respecting B i the characteristics of volcanic eruptions. For this reason as much space as is practicable under the plan I have outlined, will be devoted at the beginning to the con sideration of the volcanoes of southern Europe. Some attention will also be given to the volcanoes of Iceland, the Hawaiian islands, Japan, and the Java-Sumatra region. Stromboli. — Rising from the Mediterranean, about six teen miles northwest of the Strait of Messina, is a volcanic island known as Stromboli, one of the Lipari group. Its general form is that of an irregular four-sided pyramid. From an opening near its summit steam es capes almost constantly, and frequently with small explosions.

The steam condenses so as to form a peculiar, fleecy cloud when illuminated by the sun, and glows at night with a ruddy light emanating from the highly heated and frequently molten rock within the opening, near the apex of the island. Owing to the long con tinued activity of the volcano, the light reflected at night from the cloud above its summit serves as a beacon to mariners, and has made it known as the Light-house of the Mediterranean. The island of Stromboli is the exposed portion of a large volcanic pile, the base of which is deeply sub merged. Its summit rises about 3000 feet above the sea, and soundings near at hand show that its base is submerged to about the same amount. "Were the sea removed, it would stand as a precipitous, isolated mountain, rising from a plane to a height of 6000 feet, and with a base five or six miles in diameter.

This mass of material has been forced out in a molten or plastic condition from an opening in the floor of the sea, and piled up about the vent. The tube or conduit, through which the molten rock ascended, has been prolonged by the accumulation of the hardened lava about the original opening, and now leads to near the summit of the island. The conduit is still filled with molten lava derived from an unknown source, probably thousands of feet beneath the floor of the Mediterranean, and from time to time overflows, or explosions blow out fragments of plastic rock, and additions of fresh material are made to the pile. The position of the opening, through which molten rock, accompanied by great volumes of steam, escapes, is changed from time to time, although historical records that such is the case appear to be indefinite, and is now on the northwest side of the mountain, about one thousand feet below the summit.

This opening is a cup-shaped depression, or crater. From it a flat slope, bounded on each side by steep cliffs, and known as the Sciarra, de scends at an angle of about 35° to the sea. This steep slope, however, is a peculiar feature of Stromboli, and not characteristic of volcanoes in general. The study of volcanoes has shown that they may, for convenience, be divided into two classes — the explosive and the quiet — with reference to the violence of their erup tions. Stromboli is an example of the former class, but is usually in a mild state of activity, and thus favorable for observing the characteristics of volcanic eruptions. The nature of the eruptions usually in progress at Stromboli has been graphically described by Judd,1 who visited the island in April, 1874, as follows: 1 J. W. Judd, " Volcanoes," International Scientific Series.

Appleton & Co., 1881. This book is recommended to students. From it much of the information presented in the present volume concerning the characteristics of volcanoes has been either directly or indirectly obtained. " On reaching a point upon the side of the Sciarra, from which the crater was in full view before me, I witnessed and made a sketch of an outbreak which took place. [This sketch is reproduced in Fig. 1.] Before the outburst, numerous light curling wreaths of vapor were seen ascending from fissures on the sides and bottom of the crater. Suddenly, and without the slightest warning, a sound was heard like that produced when a locomotive blows Off its steam ; a great volume of watery vapor was Fig. 1. The crater of Stromboli as viewed from the side of the Sciarra during an eruption on the morning of April 24, 1874.

(After J. W. Judd.) at the same time thrown violently into the atmosphere, and with it there were hurled upwards a number of dark fragments, which rose to a height of 400 or 500 feet above the crater, describing curves in their course, and then falling back upon the mountain. Most of the fragments tumbled into the crater with a loud, rattling noise, but some of them fell outside the crater, and a few rolled down the steep slope of the Sciarra into the sea. Some of these falling fragments were found to be still hot and glowing, and in a semi-molten condition, so that they readily received the impression of a coin thrust into them." From above the crater, when the direction of the wind is favorable, one can look down into the fiery caldron and learn more of the nature of the eruptions that take place.

From such a point of view, as described by Judd, " The black, slaggy bottom of the crater is seen to be traversed by many fissures or cracks, from most of which curling jets of vapor issue quietly, and gradually mingle with and disappear in the atmosphere. But besides these smaller cracks at the bottom of the crater, several larger openings are seen, which vary in number and position at different periods ; sometimes only one of these apertures is visible, at other times as many as six or seven, and the phenomena presented at these larger apertures are especially worthy of careful investigation. " These larger openings, if we study the nature of the action taking place at them, may be divided into three classes. From those of the first class, steam is emitted with loud, snorting puffs, like those produced by a locomotive engine, but far less regular and rhythmical in their succession.

In the second class of apertures masses of molten material are seen welling out, and, if the position of the aperture be favorable, flowing outside the crater ; from this liquid molten mass steam is seen to escape, sometimes in considerable quantities. The openings of the third class present still more interesting appearances. Within the walls of the apertures a viscid or semi-liquid substance is seen slowly heaving up and down. As we watch the seething mass, the agitation within is observed to increase gradually, and at last a gigantic bubble is formed which violently bursts, when a great rush of steam takes place, carrying fragments of the scum-like surface of the liquid high into the atmosphere. " If we visit the crater by night, the appearances presented are found to be still more striking and suggestive.

The smaller cracks and larger openings glow with a ruddy light. The liquid matter is seen to be red-hot or even white-hot, while the scum or crust which forms upon it is of a dull red color. Every time a bubble bursts and the crust is broken up by the escape of steam, a fresh, glowing surface of the incandescent material is exposed. If at these moments we look up at the vapor cloud covering the mountain, we shall at once understand the cause of the singular appearances presented by Stromboli when viewed from a distance at night, for the great masses of vapor are seen to be lit up with a vivid, ruddy glow, like that produced when an engine driver opens the door of the furnace and illuminates the stream of vapor issuing from the funnel of his locomotive." The bursting of great bubbles of steam on the surface of the viscid lava within the crater accounts for the globular, fleece-like masses of vapor that give a special feature to the steam cloud seen above Stromboli.

Similar concentric masses of vapor are a characteristic portion of the vapor columns that rise from many volcanoes during calm weather. An essential element, at least of the less violent eruptions of volcanoes, is thus shown to be the breaking of huge bubbles of steam. The fact of special significance to be noted in the account of a mildly explosive volcanic eruption just cited, is that the throat of the volcano is filled with molten rock, por tions of which are violently ejected from time to time by the escape of steam which rises through the liquid lava. These fragments of semi-molten rock are hurled into the air and fall in part about the opening from which they were ejected, and build up a rim about it. A conical pile of this nature with an opening in its summit, is termed a cinder cone.

We also note that sometimes the molten rock overflows the crater and descends the moun tain as a lava stream. These features, as will be seen later, are characteristic of the eruptions of many volcanoes. Although Stromboli is usually in a state of mild ac tivity, yet occasionally the violence of its explosions is greatly increased. The roar of the escaping steam may then be heard for many miles ; fragments of plastic rock are hurled thousands of feet into the atmosphere, and scattered not only over the entire island, but fall in the surrounding waters ; and streams of molten rock flow down from the crater into the sea. Vesuvius. — This world-famed volcano, situated near the shore of the Bay of Naples and about ten miles eastward of the city of Naples, is a charming and most beauti ful object when beheld from afar.

The first evidence of its presence that usually meets the gaze of the expectant traveller, whether approaching over the blue sea or through the picturesque land, is a vast column of steam, rising tranquilly far above the mountain's summit, and then expanding into a broad, vapory canopy. When the wind is not too strong, the cloud is seen to be made up of concentric, fleecy masses, each one of which, as in the case of the cloud above Stromboli, is due to the explosion of a great steam bubble in the caldron of molten rock from which it rose. The vertical shaft of steam with its expanded summit resembles in general form the outlines of the characteristic stone pine of Italy, and for this reason is widely known as the pine tree of Vesuvius. Vesuvius is a conical mountain about 4000 feet high. From the Bay of Naples the steep conical summit is seen to rise within the truncated and half-destroyed crater of an older and much larger volcano, the highest portion of which has an elevation of 3730 feet.

The portion of the rim of the older crater still remaining is termed Mt. Somma. Previous to the Christian era, Vesuvius was familiar to the Romans as a conical mountain with a truncated summit, in which there was a deep depression some three miles in diameter. From the earliest historic times to the year 79, the volcano was dormant and its crater cold and overgrown with vegetation. In the year mentioned, an explosion of remarkable violence occurred, which blew away a large portion of the ancient crater and buried Pompeii and Herculaneum beneath the fragmental prod ucts that were ejected. It was during this eruption that Pliny lost his life, while making observations on the earliest volcanic explosion of which history retains a definite record.1 A portion of the wall of the ancient crater, referred to above as Mt. Somma, was left, and within its embrace the modern Vesuvius has been built.

The volcano, which gives a matchless charm to a thousand picturesque vistas in the vicinity of Naples, has, like Stromboli, its periods of mild activity, inter rupted at irregular intervals by explosive eruptions of great violence, which, in many instances, are accompanied 1 This tragic event was minutely and graphically recorded by Gaius Plinius, the younger Pliny. A translation of this account may be found in Shaler's " Aspects of the Earth." New York, 1889, pp. 50-56. PLATE 2, Fig. A. Vesuvius in eruption. As seen from Naples, 3 p.m., April 26, 1872. Fig. B. Vesuvius in eruption. As seeu from Naples, 3.30 p.m., April L'O, 1872. by overflows of lava. Unlike Stromboli, however, the variations in its activity are strongly pronounced. At times Vesuvius is dormant for many years and even for centuries, and again awakens to an activity of such energy that southern Italy is shaken by earthquakes, steam escapes in explosions so violent as to hurl stone and dust high in the air, and even blow away and dis tribute far and wide over the adjacent region the material previously forming the summit of the mountain.

While Stromboli since the dawn of history has been in a state of mild activity, interrupted at long intervals by explosions of greater violence, Vesuvius has been alternately dormant and its summit cold, and again an object of dread which has brought destruction and death to the fair land sur rounding it. These two volcanoes belong to the explosive type, as the student will appreciate more fully in advance, but illustrate two quite well marked phases of that type, which have been recognized also in many other volcanoes, and are termed the Strombolian stage and the Vesuvian stage, — the former characterized by long-continued but mild activity, the second by periods of rest broken by explosions of extreme violence. When Vesuvius is in a mild state of activity, approaching that normal to Stromboli, one may safely climb to the edge of the great bowl which usually exists at the summit and even descend into it, and observe the nature of the molten rock that rises from below, the manner in which the steam escapes from its enclosing magma, etc.

In November, 1879, I climbed the cone composed of loose fragments of lava, forming the summit portion of Vesuvius, and reached the rim of the bowl-shaped depres sion at the summit. The crater near the summit then had an outer slope of about 35° ; the inner slope was more precipitous, and exposed the edges of outward-dipping layers of fragmental material, showing that the opening had not long previously been enlarged by the blowing away of the inner portion of its rim. This occurred perhaps during the energetic eruption of 1872. The crater was by eye measurement 150 to 200 feet deep, and a thousand feet in diameter. It was floored with black, slag-like lava. The lava in many places was wrinkled or corrugated, owing to slow movement before cooling, and intersected by numerous fissures through which the glowing, red-hot rocks beneath could be plainly seen.

From some of the fissures, steam was escaping with a hissing noise. In the central portion of the floor of hardened lava, and resting on it, was a rough, conical pile of slag like lava, rising to a height nearly as great as the highest point on the encircling rim. This inner pile was the cone of eruption. From its summit great volumes of vapor were rolling out, accompanied by puffs which sent globular masses of steam high in the air. With each puff, stones four or five inches in diameter and highly heated, were hurled to a height of between one and two hundred feet in the air. Some of the stones fell on the sides of the conical pile, and occasionally one would roll to its base. At each explosion the entire crater vibrated, but not sufficiently to be at all alarming. I descended to the floor of the crater, and could walk with safety over the recently congealed lava, although it was hot to the feet.

One could easily thrust a Avalking-stick through the crevices and into the still semi-molten lava beneath. On gaining the base of the cone of eruption, I clambered about half-way up its rough sides, but, as the wind was not strong or regular in any one direction, the stones hurled into the air at each explosion fell all about the central orifice, while the steam and gases became more and more dense near the summit. The pulsating and rumbling of the molten material within the crater could be distinctly heard, and the trembling of the rocks at each explosion when a belch of steam occurred, made it troublesome to stand erect. Although prevented from seeing the actual boiling of the lava within the crater, this omission can be supplied by observations made by N. S. Shaler,1 in the winter of 1882 : " Taking advantage of a strong gale from the north, the well-known tramontana of Italy, it was possible to creep up to the very edge of the crater and look down upon the surface of the boiling lava, from which the gases were breaking forth.

Although the pit was from time to time filled with whirling vapor, the favoring wind often swept it away so that for a few seconds it was possible to see every feature of the terrifying scene. Several times a minute the surface of the tossed lava was rent by a violent explosion of gases, which appeared to hurl the whole mass of fluid rock into the air. The ascending column of vapor and lava fragments rose as a shaft to a height of several hundred feet. Many of the masses, which seemed to rise with the ease of bubbles. were some feet in diameter, and made a great din as they crushed down upon the surface on the southward side of the crater. They often could be seen to fly into frag ments as they ascended. At the moment of the explosion the escaping gases appeared transparent, a few score feet above the point of escape the ejected column became of a 1 " Aspects of the Earth."

New York, 1889. pp. 62-64. steel-gray color, and a little higher it changed to the characteristic hue of steam. That it was steam slightly mixed with other gases was evident whenever in its whirling movements the vaporous column swept around the point of observation. The curious " work-day odor " of steam was perfectly apparent, together with the pungent sense of sulphurous fumes suggestive of an infernal laundry. " Although the heat at the moment of explosion was great, it was possible, with the shelter to the face secured by an extemporized mask, to avoid any serious conse quences from it, and even to make some rather rude and unsatisfactory diagrams of the scene. The principal ob stacle to observation arose from the violence of the shocks given to the cone and propagated through the air by the explosions, which made it extremely difficult to fix the attention on the phenomena. . . .

"As if to complete the illustration of volcanic phenom ena which this little outbreak afforded, there was a small rivulet of lava pouring from the low wall of cinders on one side of the cone and flowing quietly down the slope. It was not much larger than the stream of liquid iron which flows from an iron-furnace to the moulds which await it, but in the motion all the essential features of the greatest of these fiery torrents could be seen. The surface of the fluid, cooled in the air, slowly hardened into a viscid scum. This scum, urged forward by the swifter movement of the more fluid matter below, was wrinkled as is the cream on a pan of milk when it is slowly poured over the edge of the vessel." Two of the most important phases of volcanic eruptions are illustrated by the observations just cited ; one the blowing out of rock fragments by steam explosions, the other the overflow of molten rock.

These are the chief manifestations, with the exception of the escape of vast volumes of steam, that attract the attention in all volcanic eruptions, and may occur separately or be united in the same outbreak. The mild explosions and rivulets of lava characteristic of the eruptions of Stromboli and of the more subdued phases of Vesuvius when in action, have but to be in creased in intensity and volume, to enable one to appreciate the nature of even the most stupendous volcanic outbreak that the world has ever witnessed. The proximate cause of the explosions in the eruptions described above is plainly the expansive energy of steam. The origin of the steam, the cause of the pressure on the molten rock which forces it upward, and the source of the heat that liquefies the lava, will be considered in advance.