Vulcanization

“ Now there are large numbers of crateriform mountains on our globe in the formation of which water has played an important, indeed essential, part. As we have already seen, water, though not the ultimate cause of volcanic eruptions, has been the chief agent, when in the form of steam at high pressure, in producing the explosions which accompany these eruptions, and in tearing up and hurling into the air the masses of rock, scoriæ, and ashes, which are piled around the vents of eruption in the form of craters during periods of activity. ”

“ Erosion is so slow—on an average 3,000 years being required to remove a foot of surface—that solidification by cooling must keep pace with it; 2. Volcanoes are generally not situated in areas of erosion, but along coast-lines and on islands; and, 3. They are conspicuously associated with lines of fracture and elevation.
A simple explanation of the phenomena of vulcanism is suggested by the writer, and that is—the relief of pressure by slight arching of the crust of the earth along lines of elevation, while the pressure is maximum under the unbroken areas on either side. ”

“ The immediate cause of volcanic eruptions is believed to be owing to the water of the sea, or from lakes, or inundations, finding itself a passage into the subterraneous fires, which may lie at great depths. This must first produce by its coldness a condensation of the vapour there existing, or a vacuum, and thus occasion parts of the earth's crust or shell to be forced down by the pressure of the incumbent atmosphere. Afterwards the water being suddenly raised into steam produces all the explosive effects of earthquakes. ”

“ In this way we may account for the numerous dykes of trap by which some volcanic districts are intersected, such as those of the north of Ireland and centre of Scotland.
From the above considerations, it follows that the earth's crust must be in a condition both of pressure (or lateral thrust) towards the exterior portion, and of tension towards the interior, the former condition resulting in faulting and flexuring of the rocks, the latter in the formation of open fissures, through which lava can ascend under high pressure. ”

“ The tremendous accumulations of broken rocks over lava beds on the cone of Vesuvius, and on all the Caribbee Islands, recall the breccias, or volcanic conglomerates, of the Yellowstone and of the High Plateaus of Utah. Floods of basalt alternate with vast falls or outwashes of volcanic gravel. Avalanches, landslides, torrents, floods—call them what you will—cover immense areas of the Cordillera. Vesuvius and Pelée pile up cones, but the Caribbees and Italy are also heaped with agglomerates. Erosion destroys cones, but erosion makes agglomerations or valley fills of rocks and mud. ”

“ We know that in the Bay of Baiæ, in 1538, in Cutch in 1819, and on several occasions in Peru and Chili, since the commencement of the present century, the permanent upheaval or subsidence of land has been accompanied by the simultaneous emission of lava at one or more points in the same volcanic region. From these and other examples it may be inferred that the rising or sinking of the earth's crust, operations by which sea is converted into land, and land into sea, are a part only of the consequences of subterranean igneous action. ”

“ Rainier are peaks built up by the materials thrown out of the craters of volcanoes dead these thousands of years. Vesuvius is at present showing us how volcanic mountains are made. Each eruption builds larger the cone—that is, the chimney through which the molten rocks, the ashes, and the steam are ejected. Side craters may open, the main cone be broken and its form changed, but the mass of lava and stones and ashes grows with each eruption. The mountain grows by the additions it receives. ”

“ LINES AND GROUPS OF ACTIVE VOLCANIC VENTS.
The globe is girdled by a chain of volcanic mountains in a state of greater or less activity, which may perhaps be considered a girdle of safety for the whole world, through which the masses of molten matter in a state of high pressure beneath the crust find a way of escape; and thus the structure of the globe is preserved from even greater convulsions than those which from time to time take place at various points on its surface. ”

“ The canyon line encircles Mount Washburn, the old volcano, and conceivably is over an old crack concentric to the dome.
Water is a transporter, and cracking opens ways to the rotting agents. Only in rivulets and floods does water actually corrade, or grind, the bottoms of streams. In our spray and fern patterns there is analogy to rainfall springs on flat strata, but nine-tenths of the elements of erosion are left out: jointing, weathering, ice, faulting, gravitation, rotting down, quaking, solution, sliding, and last, spring water. ”

“ Floating pumice formed a layer on the ocean surface two and a half feet in thickness, through which vessels had difficulty in forcing their way.
The steam which rises in large volumes into the air may become suddenly condensed with the chill of the upper atmosphere and fall as rain, torrents of which often follow an eruption. The rain, falling through the clouds of volcanic dust, brings it to the earth as liquid mud, which pours in thick streams down the sides of the mountain. ”

“ But it may be stated with some confidence, in general terms, that the history of the earth appears to show that, throughout all geological time, our world has been the theatre of intermittent geological activity, periods of rest succeeding those of action; and if we are to draw a conclusion regarding the present and future, it would be that, owing to the lower rate of secular cooling of the crust, volcanic action ought to become less powerful as the world grows older. ”

“ We see, therefore, an evident connection, first, between the bursting forth every now and then of volcanic matter through rents and fissures, and the expansion or forcing outwards of the earth's crust, and, secondly, between a dormant and less energetic development of subterranean heat, and an amount of subsidence sufficiently great to cause mountains to disappear over the broad face of the ocean, leaving only small and scattered lagoon islands, or groups of atolls, to indicate the spots where those mountains once stood. ”

“ I stated in 1830 in the “Principles of Geology,” [6] that running water and volcanic action are two antagonistic forces; the one labouring continually to reduce the whole of the land to the level of the sea, the other to restore and maintain the inequalities of the crust on which the very existence of islands and continents depends. I stated, however, that when we endeavour to form some idea of the relation of these destroying and renovating forces, we must always bear in mind that it is not simply by upheaval that subterranean movements can counteract the levelling force of running water. ”

“ Both volcanic extrusion and crustal movement may be the means of relieving local strains in the earth's crust, and both are found to occur, as might reasonably be expected, in many parts of the earth where folding and fracture of the rocks have frequently happened and where mountain-making appears to be still in progress. Thus, volcanoes may often be traced along zones of crustal deformation, or folded mountain-chains, especially where they run near the borders of the oceanic basins. They are frequently associated with the Pacific type of coast-line. ”

“ Professional geology is largely continental because its field work has been on continents. My work has been oceanic; my field, seventy percent of the earth’s surface, extending over a thick crust down to the earth core. The earth core is fluid and massive and hot, as all geology agrees. Isostasy, which postulates a thin flexible shell, is violated by the ocean deeps and the volcanic ridges. Volcanic rift echelons like the Cordillera and the Hawaiian ridge are too long to be generated as the fracture of a crust fifty miles deep. ”

“ Diastrophism, then, as it affects the ocean-bottoms and the ocean-borders, may make the water of any ocean shallower or deeper; it may cause the emergence or submergence of land; it may make coast-lines regular or irregular; it may shift the habitat of life, and through these changes may greatly influence the processes of gradation, which are especially active along the contact of sea and land.
Vulcanism affects the sea-bottom much as it affects the land. At the volcanic centers, where the great body of extruded matter accumulates, mounds and mountains are built up. ”

“ There can thus be no doubt that the mysterious agency which produces earthquakes and volcanoes on the land affects equally that portion of the earth's crust covered by the waters of the ocean, and must be ceaselessly employed in elevating large areas of sea-bottom into new continents, that will ere long become clothed with vegetation and peopled with animals. In contemplating, therefore, the constant decay in progress on the surface of the land, we see not a mere isolated process of waste, but a provision for future renovation. ”

“ A crust forms over the surface of the lava, which rapidly becomes hard enough to permit one to walk over it safely. The vegetation, which has been destroyed by the hot ashes, again springs up, and, if the volcano happens to be situated within the tropics, where there is an abundance of moisture, the land soon again becomes covered by a luxuriant vegetation. Most of the people, who have escaped sudden death during the eruption, return to the ruins of their houses ”

“ Mountains are thereby forming by upheavals from beneath, and the corresponding surface valleys are consequently filling up, either by the slow deposit of the matter from the saline water of hot springs, or by the sudden eruption of a new or presumably extinct volcano."
"What would happen if a crevice in the bottom of the ocean should conduct the waters of the ocean into a deposit of metallic bases?"
"That often occurs," was the reply; "a volcanic wave results, and a volcano may thus rise from the ocean's depths."
"Is there any danger to the earth itself? ”

“ While, on the one hand, we are led by recent geological investigations to reject the notions which were formerly accepted, by which mountain-ranges were supposed to be suddenly and violently upheaved by volcanic forces, we are, on the other hand, driven to conclude that without the action of these subterranean forces, the irregularities which are exhibited on the earth's surface could not have had any existence. ”

“ After thousands of years, the great cone is stripped away to expose the hardened “volcanic plug” in the conduit. During this period of inactivity, streams broaden their valleys and dissect the lava plateau to form isolated lava-capped mesas.
d. Continued erosion removes all traces of the cone and the land is worn down to a surface of low relief. All that remains is a projecting plug or “volcanic neck,” a small lava-capped mesa, and vestiges of the once lofty volcano and its surrounding lava plateau. ”

“ The river in its winding course might come upon one cone after another, and during times of flood, or when its waters burst through any temporary barrier created by volcanic operations it would attack the slopes of loose material and sweep their detritus onward. At the same time, the current would carry forward its own natural burden of far-transported sediment, and hence on its flood-plains, buried and preserved under sheets of basalt, we find abundant pebbles of the old Highland rocks which it had borne across the whole breadth of the basaltic lowland. ”

“ These terraces are not likely to have been formed by any freak of the eruption, and we are led to ascribe them in general to landslip phenomena. When, in the course of a volcano’s formation, the piling-up of material about the vent has continued till the lower portions have been unable to support the upper, or when from any cause, the material composing the pile has lost its cohesiveness, the natural consequence has been a breaking away of a portion of the structure and its precipitation down the inclined sides of the crater. ”

“ This process of earth-building went on intermittently for many centuries until the volcano had exhausted its violence and had distributed its many cubic miles of outpourings in encircling deposits around its flanks. With the subsidence of volcanism, the great earth-removing force of erosion became the predominant factor in forming the landscape. ”

“ And if the interior of our globe had been in a condition of equilibrium from the time of the consolidation of the crust to the present, reason would induce us to conclude that the lavas would ultimately have arranged themselves in accordance with the conditions of density beneath that crust. But the state of equilibrium has been constantly disturbed. Every fresh outburst of volcanic force, and every fresh extrusion of lava, tends to disturb it, and to alter the relations of the interior viscous or molten magmas. ”

“ From what has been said, it will be seen that mountain-chains may be regarded as cicatrised wounds in the earth's solid crust. A line of weakness first betrays itself at a certain part of the earth's surface by fissures, from which volcanic outbursts take place; and thus the position of the future mountain-chain is determined. Next, subsidence during many millions of years permits of the accumulation of the raw materials out of which the mountain-range is to be formed ”