Volcanic soil

“ The Earth’s crust, on which we live and depend, is in large part the product of millions of once-active volcanoes and tremendous volumes of magma (molten rock below ground) that did not erupt but instead cooled below the surface. Such persistent and widespread volcanism has resulted in many valuable natural resources throughout the world. For example, volcanic ash blown over thousands of square kilometers of land increases soil fertility for forests and agriculture by adding nutrients and acting as a mulch. ”

“ After the great eruption of 1871-72 the land covered with cinders did not bear crops for seven years, and there is no reason that they will do so sooner on the present occasion. So for years to come much of the volcanic soil must remain a barren and desert void. ”

“ But even when the volcanic covering, thus thrown athwart a wide tract of country, has been concealed under a new growth of soil and vegetation, it still remains a prey to the ceaseless processes of decay and degradation which everywhere affect the surface of the land. No feature of a modern volcano is more impressive than the lesson which it conveys of the reality and potency of this continual waste. The northern slopes of Vesuvius, for example, are trenched with deep ravines, which in the course of centuries have been dug out of the lavas and tuffs of Monte Somma by rain and melted snow. ”

“ One could descend it by tortuous paths, which led to the very bottom of the abyss, and were used not only by woodcutters plying their trade among the dense forest trees which had grown up to maturity on the lava soil, but also by animals which strayed down to browse on the succulent, rich grass. Neither men nor cattle retained any fear of the green crater depths. Only the rim of calcined stones at the summit seems to have betrayed the volcanic fire of old days, except that here and there a wreath of smoke coiled away across the elms and oaks and the pleasant scrub of broom and other underwood. ”

“ Underneath it all is sedimentary, except the interruptions, several in number, of the older outflows of lava. It is owing to the large extent to which volcanic ash enters into the composition of the earth and soil of this portion of Oregon and Washington that both earth and water are so often strongly alkaline. It forms a soil inexhaustible in fertility, and particularly adapted to the growth of cereals; but, owing to its elevation, and to the depth of the stream below the surface, together with a dry climate, is difficult of adaptation to the uses of the agriculturist. ”

“ When the eruption was over, a few individuals probably 11 returned to this area and found, much to their surprise and pleasure, that they could grow crops in locations where they hadn’t been able to farm before. The layer of volcanic ash acted as a moisture-retaining mulch; the people could plant their seeds in the underlying soil and the cinder cover would hold enough moisture to insure them a good harvest.
When this word spread around, it created a great land rush, the only one we know of in the Southwest. ”

“ So far away from the volcanic source, the wind can not have laid down a layer of this dust several feet in thickness without scattering it far and wide all around. It must have covered tens of thousands of square miles. Just imagine, if you can, a whole State, clad in the verdure of summer, suddenly, in two or three days, covered over by a blanket of white volcanic ash! Many species of plants must have found it impossible to grow in such a soil. ”

“ The soil, of a rich red colour, showed every indication of being extremely fertile in that particular climate.
From the point where we stood, one could well judge the effects of the great volcanic explosion on the back of the range—the one to our left—where a long line of buttresses had formed, as if on that side a subsidence on a large scale had also taken place. It was in any case curious to notice that at the two termini east and west of the two parallel ranges white rock in columnar form was exposed in both ranges in corresponding sites. ”

“ Almost every mile from the river eastward towards the mountains seems to increase the blanket of loam upon the underlying volcanic dust, until upon the foothills of the Blue Mountains there is a soil hard to match anywhere in the world, a mingling of volcanic dust, loam, and clay, a strong and heavy soil, not difficult to work, and retaining and utilizing moisture with remarkable natural economy. ”

“ The soil, as if ravaged by fire, hasn’t a blade of grass left. Sometimes the people of Algeria die of hunger. The grasshopper has devoured their harvests.
“Volcanoes cause cinder-showers. Volcanic ashes is the name given to the calcined dust thrown up to a great height by volcanoes at the moment of their eruption. These powdered substances form enormous clouds, which produce in the daytime a darkness like that of the darkest nights, and which, falling to earth at a greater or less distance, stifle animals and plants under their showers of dust.” ”

“ Over the whole of the vast tracts alluded to, active volcanic vents are distributed at intervals, and most commonly arranged in a linear direction. Throughout the intermediate spaces there is often abundant evidence that the subterranean fire is at work continuously, for the ground is convulsed from time to time by earthquakes; gaseous vapors, especially carbonic acid gas, are disengaged plentifully from the soil; springs often issue at a very high temperature, and their waters are usually impregnated with the same mineral matters as are discharged by volcanoes during eruptions. ”

“ The slopes and environs of the volcanic mountains Etna and Vesuvius are and always have been famous for their fertility, by which large populations are tempted to live, where they are in constant danger of being destroyed by an eruption. The richness of the soil has been traced to fertilization by volcanic ashes, which have been determined to be remarkably rich in their phosphoric acid and potash constituents. Accounts from the district in New Zealand that was flooded with ashes by last June's eruption indicate likewise that the disaster there is likely to prove a "blessing in disguise." ”

“ As a matter of fact, the actual amount of damage - 282 - to life and property which is effected by volcanic eruptions is small. Usually, the inhabitants of the district have sufficient warning to enable them to escape with their lives and to carry away their most valuable possessions. And though fertile tracts are covered by loose dust and ashes, or by lava- and mud-currents, yet the sterility thus produced is generally of short duration, for by their decomposition volcanic materials give rise to the formation of the richest and most productive soils. ”

“ Around the foot, where it is not encumbered with débris like the base of an iceberg, a broad line of comminuted pumice produces vegetation like a wady-growth in Somali Land. The central bed allows no short cut across: it is a series of rubbish-heaps, parasitic cones, walls, and lumps of red-black lavas, trachytes, and phonolites reposing upon a deluge of frozen volcanic froth ejected by early eruptions. ”

“ 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. ”

“ The stones vary from mere pea-like pebbles up to pieces two or three inches long, the largest being generally fragments of slag and amygdaloid which are less water-worn than the sandstones and other foreign ingredients. The uppermost two or three feet of the intercalation consist of dark carbonaceous mudstone or shale, made up in large measure of volcanic detritus, which may have been - 228 - derived partly from eruptions of fine dust, partly from subærial disintegration of the basalt-sheets. Some layers of these finer strata are full of remains of much macerated plants. ”

“ The ages roll on, and once more living forms of plant and animal haunt the shores of these shallowing lakes. The oak, the yew, the willow, have left their prints in the sedimentary rocks, and the bones of new creations of animal life, such as the camel and the horse, accompany them. But these, too, in turn suffer extinction by violence,—the whole country being covered more than thirty feet deep in volcanic ashes. Indeed, deposits of volcanic ashes exist in East Oregon which are one hundred feet in depth. ”

“ Test of age by organic remains.—We have seen how, in the vicinity of active volcanos, scoriæ, pumice, fine sand, and fragments of rock are thrown up into the air, and then showered down upon the land, or into neighbouring lakes or seas. In the tuffs so formed shells, corals, or any other durable organic bodies which may happen to be strewed over the bottom of a lake or sea will be imbedded, and thus continue as permanent memorials of the geological period when the volcanic eruption occurred. ”

“ Clambering down the other side of the hill, where 314 a fall of rock has recently occurred, Claude finds in the geological section thus formed an open page in which to read the history of the country. At a little distance below the surface of the old sea-bed, volcanic dust is mixed with the grains of silica that form the rock,—drab-coloured dust, such as fell at Krakatoa and Tarawera. This gradually gives place in the lower strata to a volcanic conglomerate, composed chiefly of rounded masses of felsite, ferruginous clay, burnt to a cinder, and silicious, iron-stained nodules. ”

“ It may interest you to know that some of the most fruitful of the great wheat fields of the western parts of the United States owe their extraordinary fertility to immense deposits of volcanic dust that have been thrown out from some of the great volcanoes of the geological past, now found in an extinct condition in these parts of the United States. ”

“ 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. ”

“ Plant-remains also occasionally occur in the stratified layers intercalated among the lavas and tuffs of the plateaux. Some of the best examples of their occurrence are to be found in the shales and tuffs interstratified among the enormous pile of volcanic material near Bowling. Not only does abundant vegetable debris occur distributed through the detrital strata in the volcanic series at that locality, but it is even aggregated into thin seams of coal which have been examined and described by various observers. ”

“ The forces within the earth became active again. Apparently Nature did not intend that the gold should be forever buried, or that the country should always appear so uninteresting. Internal forces raised the mountain block for a second time, tilting it still more to the westward. Volcanoes broke forth along the summit of the range near the line of fracture, and floods of lava and volcanic mud ran down the slopes, completely filling the broad valleys of the northern Sierras and burying a great part of the gold-bearing gravel. ”

“ During such eruptions, magma is shattered into tiny fragments (chiefly ash and pumice) and ejected thousands of meters into the atmosphere or even the stratosphere. Under the force of gravity, sometimes these fragments sweep down a volcano’s flanks at speeds of more than 100 kilometers per hour, mixing with air and volcanic gases to form pyroclastic flows. Rock fragments can also mix with water in river valleys to form lahars (volcanic debris flows and mudflows) that destroy everything in their paths.
Andesite and dacite magmas also erupt to form lava flows. ”

“ We have of late years become familiar with the fact, in the process of boring Artesian wells, that the seeds of plants, the remains of insects, and even small fish, with other organic bodies, are carried in an uninjured state by the underground circulation of waters, to the depth of many hundred feet. With still greater facility in a volcanic region we may conjecture, that water and mud full of invisible infusoria may be sucked down, from time to time, into subterranean rents and hollows in cavernous lava which has been permeated by gases, or in rocks dislocated by earthquakes. ”

“ 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. ”

“ It is like traversing the interior of an extinct volcano, for the rocks are all volcanic, of different ages and different colours, black and grey lavas, yellow and pink and whitish and bluish beds of tufa and indurated ash, sometimes with long streaks of gravel or dark sand streaming down from the base of the precipices above. At one place there is seen just under such a precipice, a row of sharp black pinnacles, not unlike miniature aiguilles, apparently the remains of a lava bed that has disintegrated, leaving its harder parts to stand erect. ”