Volcanoes And Earthquakes Explained
( Originally Published 1906 )
The Theories of Science on Seismic Convulsions—Volcanoes Likened to Boils on the Human Body through Which the Fires and Impurities of the Blood Manifest Themselves—Seepage of Ocean Waters through Crevices in the Rock Reach the Internal Fires of the Earth—Steam is Generated and an Explosion Follows—Geysers and Steam Boilers as Illustrations-- Views of the World's Most Eminent Scientists Concerning the Causes of Eruption of Mount Pelee and La Soufriere.
THE earth, like the human body, is subject to constitutional derangement. The fires and impurities of the blood manifest themselves in the shape of boils and eruptions upon the human body. The internal heat of the earth and the chemical changes which are constantly taking place in the interior of the globe, manifest themselves outwardly in the form of earthquakes and volcanoes. In other words, a volcano is a boil or eruption upon the earth's surface.
Scientists have advanced many theories concerning the primary causes of volcanoes, and many explanations relating to the igneous matter discharged from their craters. Like the doctors who disagree in the diagnosis of à human malady, the geologists and volcanists are equally unable to agree in all details concerning this form of the earth's ailment. After all theories relating to the cause of volcanoes have been considered, the one that is most tenable and is sustained by the largest number of scientific men is that which traces volcanic effects back to the old accepted cause of internal fires in the center of the earth. Only in this way can the molten streams of lava emitted by volcanoes be accounted for.
The youngest student of familiar science knows that heat generates an upward and outward force, and like all other forces that it follows the path of least resistance. This force is always present in the internal regions of the earth, which for ages upon ages has been gradually cooling from its poles toward its center. When conditions occur by which it can outwardly manifest itself, it follows the natural law and escapes where the crust of the earth is thinnest.
But something more than the mere presence of internal fire is necessary to account for volcanic action, although it may in a large degree account for minor seismic convulsions in the form of an earthquake. The elements which enter into the source of volcanic eruption are fire and water. The characteristic phenomenon of a volcanic eruption is the steam which issues from the crater before the appearance of the molten lava, dust, ashes and scoria. This accepted theory is plainly illustrated in the eruption of a geyser, which is merely a small water volcano. The water basin of a geyser is connected by a natural bore with a region of great internal heat, and as fast as the heat turns the water into steam, columns of steam and hot water are thrown up from the crater.
One form of volcanic eruption, and its simplest form, is likewise illustrated in a boiler explosion. Observations of the most violent volcanic eruptions show them to be only tremendous boiler explosions at a great depth beneath the earth's surface, where a great quantity of water has been temporarily imprisoned and suddenly converted into steam. In minor eruptions the presence of steam is not noticeable in such quantities, which is simply because the amount of imprisoned water was small and the amount of steam generated was only sufficient to expel the volcanic dust and ashes which formed between the earth's surface and the internal fires of the volcano. The flow of lava which follows violent eruptions is expelled by the outward and upward force of the great internal heat, through the opening made by the steam which precedes it.
The two lines of volcanoes, one north and south, the other east and west, which intersect in the neighborhood of the West Indies, follow the courses where the crust of the earth is thin-nest and where great bodies of water lie on the shallowest parts of the ocean bed.
The terrific heat of the earth's internal fires is sufficient to cause crevices leading from these bodies of water to the central fires of the volcano, and the character of the volcanic eruption is determined largely by the size of the crevices so created and the amount of water which finds its way through them. The temperature of these internal fires can only be guessed at, but some idea may be formed of their intense heat from the streams of lava emitted from the volcano. These will sometimes run ten or twelve miles in the open air before cooling sufficiently to solidify. From this it will be seen that the fires are much hotter than are required merely to reduce the rock to a liquid form. From this fact, too, may be seen the instantaneous action by which the water seeping or flowing into the volcano's heart is converted into steam and a tremendous explosive power generated.
The calamity which befell Martinique and St. Vincent will unquestionably lead to a fresh discussion of the causes of volcanic disturbance. Not all of the phenomena involved therein are yet fully understood, and concerning some of them there are perceptible differences of opinion among experts. On at least one point, however, there is general agreement. At a depth of about thirty miles the internal heat of the earth is probably great enough to melt every known substance. Confinement may keep in a rigid condition the material which lies beneath the solid crust, but if an avenue of escape is once opened the stuff would soften and ooze upward. There is a growing tendency, moreover, to recognize the importance of gravitation in producing eruptions. The weight of several miles of rock is almost inconceivable, and it certainly ought to compel `potentially plastic" matter to rise through any crevice that might be newly formed. Russell, Gilbert and some other authorities regard this as the chief mechanical agent in an eruption, at least when there is a considerable outpouring of lava.
As to the extent to which water operates there is some lack of harmony among volcanists. Shaler, Milne and others hold that substance largely, if not entirely, responsible for the trouble. They point to thé fact that many volcanoes are situated near the coast of continents or on islands, where leakage from the ocean may possibly occur. Russell, on the other hand, regards water not as the initial factor, but as an occasional, though important, reinforcement. He suspects that when the molten rock has risen to a considerable distance it encounters that fluid, perhaps in a succession of pockets, and that steam is then suddenly generated. The explosive effects which ensue are of two kinds. By the expansion of the moisture which some of the lava contains the latter is reduced to a state of powder, and thus originate the enormous clouds of fine dust which are ejected. Shocks of greater or less violence are also produced. The less severe ones no doubt sound like the discharge of artillery and give rise to tremors in the immediate vicinity. In extreme cases enough force is developed to rend the walls of the volcano itself. Russell attributes the blowing up of Krakatoa to steam. The culminating episode of the Pelee eruption, though not resulting so disastrously to the mountain, would seem to be due to the same immediate cause. To this particular explosion, too, it seems safe to assign the upheaval which excited a tidal wave.
The precise manner in which the plastic material inside of the terrestrial shell gets access to the surface, is not entirely clear. Nevertheless, it is possible to get some light on the matter. It is now well known that in many places there are deep cracks, or "faults," in the earth's crust. Some of them in the remote past have been wide and deep enough to admit molten material from below. The Palisades of the Hudson are believed to have been formed by such an intrusion, the adjacent rock on the eastern face having since been worn away by the weather or other agents. It has been observed that many volcanoes are distributed along similar faults.
The existence of a chain of volcanic islands in the West Indies suggests the probability that it follows a crack of great antiquity, though the issue of lava and ashes for several centuries may have been limited to a few isolated points. Just how these vents have been reopened is one of the most difficult questions still left for investigation. Given a line of weakness in the rocks, though, and a susceptibility to fresh fracture is afforded. Professor McGee suggests that the over-loading of the ocean bed by silt from the Mississippi river or other sources may have been the immediately exciting cause of the recent outbreaks. Other geologists have found a similar - explanation acceptable in the case of eruptions elsewhere. The theory has much to commend it to favor.
The Martinique disaster already has drawn from geologists and volcanists many expressions of opinion, and explanations of volcanic phenomena which set forth in detail the causes and effects of volcanic eruptions, in particular, and seismic 'convulsions, in general.
Dr. A. R. Crook, a professor in Northwestern University, has made a special study of volcanoes. He has made an ascent of the two highest in the world, and has climbed many others for purposes of study. He is an authority upon volcanography.
"There are two great circles of volcanoes about the earth," said Professor Crook. "One girdles the earth north and south, extending through Tierra del Fuego (called `land of fire' because of its volcanoes), Mexico, the Aleutian islands and down through Australia; the other east and west through Hawaii, Mexico, West Indies, Italy (including Mount Vesuvius and Asia Minor.
"These two circles intersect at two points. One of these is the West Indies, which include Martinique, the scene of this terrible disaster; the other is in the islands of Java, Borneo and Sumatra. On the latter islands there are extinct volcanoes. On the former is the terrible Pelee. It is just at these points of intersection of the two volcanic rings that we expect unusual volcanic activity, and it is there that we find it.
"There has been more or less theorizing as to volcanic disturbances moving in cycles, but it cannot be proved. One fact is established, and that is that a volcano is an explosion caused by water coming in contact with the molten mass below the surface of the earth. This is proved by the great clouds of steam that accompany the action.
"The old theory that the very center of the earth is a molten mass," he says, "is no longer held." He asserts the latest idea is that the center of the earth is more rigid than glass, though less rigid than steel. About this there is more or less molten matter, and over all the surface crust of the earth. This molten matter causes the surface of the earth to give, to sag, and form what is called "wrinkling." When water comes in contact with the heated mass an explosion follows that finds its outlet through the places where there is least resistance, and the result is a volcano.
"There is no part of the earth's surface which is exempt from earthquakes," said Professor Crook, "and there is no regularity in their appearance. Volcanic eruptions are almost always preceded by earthquakes somewhere in the circle. Recently there were earthquakes in the City of Mexico in which many lives were lost. As it is impossible to predict when the next will take place, it is also impossible to tell where it will be. It will certainly be somewhere in the line of the two circles.
"All this is of interest as showing that the earth is still in process of formation just as much as it was a billion years ago. We see the same thing in Yellowstone Park. There most decided changes have taken place even in the last eight years.
Old Faithful, which used to play regularly every sixty minutes, now does so only once in twice the time."
With reference to contributions to science, which might be expected from investigations at Martinique, Professor Crook said:
"Even new elements might be discovered, and seismic theories either confirmed or disproved. A volcano always throws off a great variety of materials, hydrochloric and sulphuric acids, iron, silica (sand), sulphur, calcium and magnesium. The lava is of two kinds. That which is easily fusible flows more rapidly than a horse can trot. A more viscous kind cools into shapes like ropes. The latter is common in Hawaii.
"The danger of living in proximity to a volcano is usually well known, but the iron oxides render the soil extremely fer tile. This is seen in Sicily about "Etna and Vesuvius. It is seen also in Martinique, where an area of forty miles square was occupied by 16o,000 people.
"Owing to the presence of the fumes of chlorine it is probable that many of the victims in St. Pierre were asphyxiated, and so died easily. Others doubtless were buried in ashes, like the Roman soldier in Pompeii, or were caught in some enclosed place which being surrounded by molten lava resulted in slow roasting. It is indeed a horrible disaster and one which we may well pray not to see duplicated. Science, how-ever, has no. means of knowing that it may not occur again."
Professor Robert T. Hill, of the United States Geological Survey, who visited the French West Indies on a tour of scientific inspection, says:
"Across the throat of the Caribbean extends a chain of islands which are really smoldering furnaces, with fires banked up, ever ready to break forth at some unexpected and inopportune moment. This group, commencing with Saba, near Porto Rico, and ending with Grenada, consists of ancient ash heaps, piled up in times past by volcanic action. For nearly one hundred years there has been not the slightest sign of explosion and we had grown to class these volcanoes as extinct.
"Volcanism is still one of the most inexplicable and profound problems which defy the power of geologists to explain, and one of its most singular -peculiarities is the fact that it sometimes breaks forth simultaneously in widely distant portions of the earth. A sympathetic relation of this kind has long been known between Hecla and Vesuvius, and it is very probable that the Carib volcanoes have some such sympathetic relation with the volcanoes of Central America and southern Mexico. At the time of the explosion of St. Vincent other explosions preceded or followed it in northern South America and Central America.
"The outburst of Mount Pelee, in Martinique, is apparently the culmination of a number of recent volcanic disturbances which have been unusually severe. Colima, in Mexico, was in eruption but a few months previous, while Chelpancingo, the capital of the State of Guerrero, was nearly destroyed by earthquakes which followed.
"Only a few days before Mount Pelee erupted, the cities of Guatemala were shaken down by tremendous earthquakes."
Professor N. S. Shaler, of Harvard University, a world authority on volcanic disturbances, says:
"Volcanic outbreaks are ,merely the explosion of steam under high pressure—steam which is bound in rocks buried underneath the surface of the earth and there subjected to such tremendous heat that when the conditions are right its pent up energy breaks forth, and it shatters its stone prison walls into dust.
"The common belief is that water enters the rocks during the crystallization period, and that these rocks, through the natural action of rivers and streams, become deposited in the bottom of the ocean. Here they lie for many ages, becoming buried deeper and deeper under masses of like sediment, which are constantly being washed down upon them from above. This process is called the blanketing process.
"When the first layer has reached a depth of a few thou-sand feet the rocks which contain the water of crystallization are subjected to a terrific heat. This heat generates steam, which is held in a state of frightful tension in its rocky prison.
"It is at these moments that volcanic eruptions occur. They result from wrinkling in the outer crust of the earth's surface-wrinklings caused by the constant shrinking of the earth itself and by the contraction of the outer surface as it settles on the plastic center underneath. Fissures are caused by these foldings, and as these fissures reach down into the earth the pressure is removed from the rocks and the compressed steam in them and it explodes with tremendous force.
"The rocks containing the water are blown into dust, which sometimes is carried so high as to escape the power of the earth's attraction and float by itself through space. After the explosions have occurred lava pours forth. This is merely melted rock which overflows like water from a boiling kettle. But the explosion always precedes the flow, and one will notice that there is always an outpouring of dust before the lava comes."
Professor W. J. McGee, of the Smithsonian Institution at Washington, says: "It may be that a violent earthquake tremor came after the volcanic eruption, but it does not necessarily follow that the two travel together. Oftentimes we hear of earth tremors with no apparent accompaniment. This was true of the Charleston earthquake in 1886. Earthquakes are caused by mysterious disturbances in the interior of the earth. The most commonly accepted belief is that massive rock beds away down in the earth, at a depth of twelve miles or more, become disturbed from one cause or another, with the result that the disturbance is felt on the earth's surface, sometimes severely, sometimes faintly.
"Probably the most violent earthquake in history occurred about ten years ago at Krakatoa. The explosion could be heard for more than one thousand miles, and the earth's tremors were felt for thousands of miles. The air was filled with particles of earth for months afterward. The air-waves following the explosion are believed to have passed two and one-half times around the globe. The face of the land and sea in the vicinity of the eruption was completely changed."
Dr. E. Otis Hovey, professor in the Museum of Natural History, New York, offers the following explanation of the Martiniqne disaster:
"A majority of volcanic eruptions are similar in cause and effect to a boiler explosion. It is now the accepted belief that sudden introduction of cold water on the great molten mass acts as would the pouring of water into a red hot boiler. It causes a great volume of steam, which must have an outlet. You can readily see how water could get into the crater, located as this one was—on an island, and not far from the coast. The volcanic chains crossed at that point. Such crossing would cause a tension of the crust of the earth, which might cause great fissures. If water were to search out those fissures and reach the great molten mass below it is not hard to imagine what the result would be. There are two classes of volcanoes—those which have explosive eruptions, like Vesuvius and Krakatoa, and this latest one, and those of no explosive nature, like Mauna Loa and Kilauea, in Hawaii, which boil up and flow over. It is the explosive eruption which brings widespread destruction, and it is astonishing to learn of the tremendous power one of those eruptions unleashes."
Professor John Milne, of London, the highest authority in the world on volcanic explosions, classifies eruptions into two grades: Those that build up very slowly. Those that destroy most rapidly.
"The latter are the most dangerous to human life and the physical face of a country. Eruptions that build up mountains are periodical wellings over of molten lava, comparatively harmless. But in this building up, which may cover a period of centuries, natural volcanic vents are closed up and gases and blazing fires accumulate beneath that must eventually find the air. Sooner or later they must burst forth, and then the terrific disasters of the second class take place. It is the same cause that makes a boiler burst."
Professor Milne was asked after Krakatoa's performance:
"Is it likely that there are volcanoes in the world at present that have been quiet for a long time but will one day or another blow their heads off?"
"It is almost certain there are."
"Some in Europe?"
"Many in Europe."
"Some in the United States?" - "Undoubtedly. "
Mount Pelee of Martinique has verified the eminent authority's word.
Professor Angelo Heilprin, of Philadelphia, the eminent geologist and authority on volcanology, declares there is danger that all the West Indian reef islands will collapse and sink into the sea from the effects of the volcanic disturbances now in progress. More than that, he says, the Nicaraguan canal route is in danger because it is in the eruption zone.
"In my opinion the volcano eruptions are not the only things to be feared," he continued. "It is altogether likely that the volcanic disturbance now going on may result in the collapse of the islands whose peaks spring into activity. The constant eruptions of rock, lava, and ashes, you must know, mean that a hole, as it were, is being made in the bosom of the earth. When this hole reaches a great size, that which is above will be without support, and then subsidence must follow. The volcanoes of Martinique and St. Vincent, and of the neighboring islands of the Caribbean, are situated in a region of extreme weakness of the earth's crust, which has its parallel in the Mediterranean basin on the opposite side of the Atlantic. This American region of weakness extends westward from the Lesser Antilles across the Gulf of Mexico into Mexico proper, where are located some of the loftiest volcanoes of the globe, Popocatepetl and Orizaba, both now in somnolent condition, and including the more westerly volcano of Colima, which has been almost continuously in eruption for ten years.
"This same region of weakness includes nearly the whole of Central America. Volcanoes in Costa Rica, Nicaragua, and Guatemala have been repeatedly active, some almost to the present time, many with destructive effect, and it should be no surprise to have some of them burst out with the same vigor and intensity as Mount Pelee or the Soufriere."
The National Geographic Society sent three geographers to make a special study of the eruptions in Martinique and St. Vincent: Professor Robert T. Hill of the United States. Geological Survey; Professor Israel C. Russell of Ann Arbor, Mich., and C. E. Borchgrevink, the noted Antarctic explorer.
Professor Hovey, after a careful examination of the desolated areas in Martinique and St. Vincent, related important scientific phases of the great eruptions.. Speaking first of the work of his companions and himself in St. Vincent, he said:
"Collection of data concerning the eruption of La Soufriere was immediately begun. The history of the eruption is practically that of the disturbance of 1851. Earthquakes occurred here about a year ago, and have occurred at intervals at various places in the West Indies and adjacent regions ever since. At least one resident of Kingstown—F. W. Griffiths—several months ago predicted that La Soufriere would soon break out.
"Finally, on the day of the great eruption, a vast column of volcanic dust, cinders, blocks of lava and asphyxiating gases rose thousands of feet into the air, spreading in all directions. A large portion of this, having reached the upper current, was carried eastward. This, falling, was .again divided, and the cinders and deadly gases were "swept by the lower winds back upon the eastward side of the mountain. The wrecked houses show this, the windows on the side toward the crater being unaffected, while those on the farther side were wrecked by the back draught up the mountain.
"There was no wind on the morning of the great outburst, a fact which facilitated the devastation of the country. The hot, asphyxiating gases rolled out of the crater, and many were scorched and suffocated. Hot mud falling from the cloud above stuck to the flesh of the unfortunate victims, causing bad wounds. Great blocks of stone were thrown out of the eastern side of the crater, which could be distinctly seen at a distance of four miles."
Concerning the eruption of Mount Pelee, Mr. Hovey said: "An increase in the temperature of the lake in the old crater of Pelee was observed by visiting geologists as much as two years ago, while hot springs had long been known to exist near the western base of the mountain and four miles north of St. Pierre. The residents of Martinique, however, all considered the volcano extinct in spite of the eruption fifty-one years ago. The ground around the crater of Pelee was reported in 1901 to consist of hot mud, showing that the increase of temperature observed eighteen months earlier had continued.
"Soon after the middle of April, this year, manifestations of renewed activity were more pronounced. Ashes began to fall in St. Pierre and heavy detonations were heard. The houses of the city shook frequently, suffocating gases filled the air at intervals, and the warning phenomena increased until they became very alarming.
"The Guerin sugar factory, on Riviere Blanche, was overwhelmed on May 5 by a stream of liquid mud, which rushed down the west slope of the mountain with fearful rapidity. The pretty lake which occupied the crater of 1851, on the southwest slope of the cone, about a mile from the extreme summit and a thousand feet below it, had disappeared, and a new crater had formed on its site, spreading death and destruction on all sides. Three days later the eruption took place and devastated the city of St. Pierre, wiping out the inhabitants and changing a garden spot to a desert.
"A vast column of steam and ashes rose to a height of four miles above the sea, as measured by the French artillerymen at Fort de France. After this eruption the mountain quieted somewhat, but burst forth again at 5:15 o'clock on the morning of May 20. This explosion was more violent than that which destroyed St. Pierre.
"On this occasion the volume of steam and ashes rose to a height of seven miles, according to measurements made by Lieutenant McCormick. An examination of the stones which fell at Fort de France showed them to be of a variety of lava called hornblende and andesite. They were bits of the old lava forming a part of the cone. There was no pumice shown to me, but the dust and lapilli all seemed to be composed of comminuted old rock.
"It is evident that the tornado of suffocating gas which wrecked the buildings asphyxiated the people, then started fire, completing the ruin. This accords with the statement which has been made that asphyxiation of the inhabitants pre-ceded the burning of the city. The gas being sulphureted hydrogen, was ignited by lightning or the fires in the city. The same tornado drove the ships in the roadstead to the bottom of the sea or burned them before they could escape.
"Mud was formed in two ways—by the mixture in the atmosphere of dust and condensed steam and by cloudbursts on the upper dust-covered slopes of the cone washing down vast quantities of fine light dust. No flow of lava apparently has attended the eruption as yet, the purely explosive eruptions thus far bringing no molten matter to the surface. The great emission of suffocating gas and the streams of mud are among the new features which Pelee has added to the scientific knowledge of volcanoes."
Professor Hill was the first man who set foot in the area of craters, fissures, and fumaroles, and, because of his high position as a scientist, his story was valuable. He reported as follows: "There were three well marked zones: First, a center of annihilation, in which all life, vegetable and animal, was utterly destroyed—the greater northern part of St. Pierre was in this zone; second, a zone of singeing, blistering flame, which also was fatal to all life, killing all men and animals, burning the leaves on the trees, and scorching, but not utterly destroying, the trees themselves; third, a large outer, non-destructive zone of ashes, wherein some vegetation was injured.
"The focus of annihilation was the new crater midway between the sea and the peak of Mount Pelee where now exists a new area of active volcanism, with hundreds of fumaroles or miniature volcanoes. The new crater is now vomiting black, hot mud, which is falling into the sea. Both craters, the old and the new, are active.
"The destruction of St. Pierre was due to the new crater. The explosion had great superficial force, acting in radial directions, as is evidenced by the dismounting and carrying for yards the guns in the battery on the hill south of St. Pierre and the statue of the Virgin in the same locality, and also by the condition of the ruined houses in St. Pierre. According to the testimony of some persons there was an accompanying flame. Others think the incandescent cinders and the force of their ejection were sufficient to cause the destruction. This must be investigated. I am now following the nature of this."
Professor Hill started on Monday, May 26, to visit the vicinity of Mount Pelee, and returned to Fort de France Wednesday morning, nearly exhausted. Professor Hill was near the ruins of St. Pierre on Monday night during the series of explosions from Mount Pelee, and was able to describe the volcanic eruption from close observation. Speaking personally of his expedition he said: "My attempt to examine the crater of Mount Pelee has been futile. I succeeded, however, in getting close to Morne Rouge. At seven o'clock on Monday night I witnessed, from a point near the ruins of St. Pierre, a frightful explosion from Mount Pelee and noted the accompanying phenomena. While these eruptions continue, no sane man should attempt to ascend to the crater of the volcano. Following the salvos of detonations from the mountain, gigantic mushroom-shaped columns of smoke and cinders ascended into the clear, starlit sky, and then spread in a vast black sheet to the south and directly over my head. Through this sheet, which extended a distance of ten miles from the crater, vivid and awful lightning-like bolts flashed with alarming frequency. They followed distinct paths of ignition, but were different from lightning in that the bolts were horizontal and not perpendicular. This is indisputable evidence of thé explosive oxidation of the gases after they left the crater. This is a most important observation and explains in part the awful catastrophe. This phenomenon is entirely new in volcanic history.
"I took many photographs, but do not hesitate to acknowledge that I was terrified. But I was not the only person so frightened. Two newspaper correspondents, who were close to Morne Rouge some hours before me, became scared, ran three miles down the mountain, and hastened into Fort de France. The people on the north end of the island are terrified and are fleeing with their cattle and effects. I spent Tuesday night in a house at Deux Choux with a crowd of 200 frightened refugees.
"Nearly all the phenomena of these volcanic outbreaks are new to science, and many of them have not yet been explained. The volcano is still intensely active, and I cannot make any predictions as to what it will do."