SCIENTIFIC TALKS.

Otago Witness, Issue 1897, 12 June 1890, Page 41

SCIENTIFIC TALKS.

By F. G. S. YOLCAtfOES. XI. In contemplating the phenomena of volcanic action — phenomena which must be classed among the grandest of which we have any knowledge — nobody can fail to be struck with the fearful destruction and misery which is caused, not only on the face of the earth, but among the ranks of humanity, by these violent manifestations of the forces of Nature. Lovely tracts of country are overwhelmed by burning lava, or buried beneath a layer of dust and mud ; magnificent cities are destioyed and hidden from view, and countless' numbers of unsuspecting human beings are hurried to their doom,

Out off even in the blossoms of their Bin, Unhoiioel'ii, disappointed, unanel'd. And when we reason on the completeness and perfection of the creative scheme, and the wonderful way in which the machinery of the world is knit together for the benefit and use of man, we cannot believe that these forces are aimless or erratic, or that there are no compensating advantages to be found in the startling and convuldive throbs of aa internal and irresistible power.

Again the geologist comes to our aid, and bids us gaze upon the hills and observe how even the hardest and most refractory rocks are shattered by the action of frost, ground away by the force of glaciers, and washed downwards to the sea by the never ceasing and subtle power of flowing water. This subject has been so fully discussed in former articles that we need here only repeat one fact, and this is, that the whole land of the globe would be, were it not for certain agencies, in a number of years which can be mathematically demonstrated, carried down beneath the surface of a boundless ocean.

That magnificent decree, " Let the waters under the heaven be gathered together into one place, and let the dry land appear," was, let us be sure, never uttered without some far-seeing and all-wise design for limiting these incessant degrading agencies without which the face of the earth would not " bring forth grass, the herb yielding seed, and the fruit tree yielding fruit after his kind."

It is a well-known fact that the materials of which the highest mountains are formed were not long ago, speaking in comparison with the ages that have elapsed since the formation of the world, lying at the bottom of the ocean, and in order to account for their elevation to the enormous height they now occupy we must call in some agency powerful enough to crumple up and pucker the crust of the globe, to act not only in violent and speedily-exhaustad paroxysms, but to continue during endless asons raising up bodily great continents and mountain ranges, and acting as an opposing force to the levelling and obliterating forces of atmospheric weathering. So far as we know there is nothing that can do this except vulcanicity, that force which includes earthquakes and volcanoes and their kindred phenomena of slow upheaval.

The denuding agencies have been acting through all time, relentlessly wearing away the dry ground ; and as there is still much supramarine land existing, we are led to the conclusion that the reconstructing forces acting from within are sufficient to balance those which destroy and remove from without, and that they are a well-designed and bountiful portion of the great scheme of creation. Nor must we suppose that the sudden and destructive effects of vulcanicity are the most important of its manifestations. As Professor Judd has said, in comparing them with the occasional violence of atmospheric phenomena, " These interruptions of such agencies, produced by hurricanes and floods, by volcanic outbursts and earthquakes, may safely be regarded as the insignificant accidents of what is, on the whole, a very perfectly- working piece of machinery."

When we glance at countries where volcanoes are actively at work, we fail to find the aridness and sterility, and the absence of human occupation, which the vicinity of such dangerous neighbours might lead us to expect. On the contrary, so often as humanity is driven away from the slopes of volcanic mountains so often does it return. The volcanic regions of Java and Japan are centres of a numerous population, rejoicing in a fertile soil and luxuriant vegetation, and on the slopes of Vesuvius a population of 80,000 souls enjoy " a climate," as Forsyth says, " where heaven's breath smells sweet and wooingly — a vigorous and luxuriant Nature unparalleled in its production — a coast which was once the fairyland of poets and the favourite retreat of great men. Even the tyrants of creation loved this alluring region, spared it, and adorned it, lived on it, died on it."

Yet were this attractive spot to be hereafter attacked by the waves of some ocean, whose ravages may be permitted by future geographical change, the student of the earth in that day mi^ht see some startling facts written in indelible characters upon the face of the land. Buried cities, superimposed one upon the other, would be laid bare, some covered deep in volcanic mud and ashes, and others scorched by the burning flood of lava; human skeletons and casts of human forms would be found among the ruins, and — taken at one glance — the history of those towns would be one of catastrophe succeeding catastrophe, of desolation following destruction.

Perhaps few of us have had an opportunity^ of examining an active volcano, and it may be worth while to give a short description of Kilauea, which 'can be taken as a good example. Standing on the brink of a yawning gulf, more than three miles across, the beholder looks down, through the jets of steam which obscure while they add grandeur to the scene, on a desolate plain, (500 ft below him, in the centre of which is another pit 400 ft deep where the bubbling lake of lava seethes and throbs with all the grand intensity of Nature's untrammelled forces. In this incandescent mass, which is about 1000 ft across, the lava boils up like springs in a pond, and with the fluidity of molten iron. At places on the surface small cones of liquid lava rise and throw up a spray of the molten fluid to a height of 50ft to 80ft, and this

action goes on without intermission until after a few years the molten mass may fill the crater and overflow the edge. More frequently, however, the sides of the mour.tain are fractured, and jets and flows of lava pour from the rents. This is not to be wondered at when we consider that at a depth of 1000 ft below the top of the column a pressure of between 70 and 80 tons is exerted on every square foot of the surrounding walls.

Should the point of escape be well down on the mountain the spectacle of a fountain of fire may be seen. This was observed in 1794 on Vesuvius, and in 1832 on Etna ; and in the eruption of 1832 on Mauna Loa, an unbroken fountain of lava 200 ft to 700 ft in height and 1000 ft broad burst out at the base of the cone, and in March 1868 four jets throwing lava to a height of irom 500 ft to 1000 ft continued to play for several weeks.