Littell's Living Age/Volume 134/Issue 1725/A Great Sea-Wave
A GREAT SEA-WAVE.
The great sea-wave which, after the recent earthquake at Peru, swept across the Pacific to the Sandwich Islands, affords fresh illustration of the vital energy which still pervades the frame of our earth. If those theories be sound according to which each planet during its extreme youth is as a sun glowing with fiery heat, and in extreme old age is, like our moon, cold (save where the sun's rays pour upon it) even to its very centre, we should regard the various portions of the middle age of a planet as indicating more or less of vitality according as the signs of internal heat and activity were greater or less. Assuredly, thus viewing our earth, we have no reason to accept the melancholy doctrine that she is approaching the stage of planetary decrepitude. She still shows signs of intense vitality, not indeed that all parts of her surface are moved at this present time by what Humboldt called "the reaction of her interior." In this respect, doubtless, changes slowly take place, the region of disturbance at one time becoming after many centuries a region of rest, and vice versâ. But regarding the earth as a whole, we find reason for believing that she still has abundant life in her. The astronomer who should perceive, even with the aid of the most powerful telescope, the signs of any change in another planet (Mars, for example, our nearest neighbor among the superior planets), the progress of the change being actually discernible as he watched, would certainly conclude that that planet was moved by mighty internal forces. Now it is not too much to say, though at first it may perhaps seem so, that the mighty sea-wave which, on May 10, rushed in upon the shores of the group of Sandwich Islands, would have been discernible from Venus, supposing an observer there had been watching the earth with a telescope as powerful as the best yet made on this earth. The wave was caused, as we know, by a tremendous subterranean disturbance in Peru a few hours earlier. Here, at least, was the centre of subterranean action, for a land wave also travelled from that region along the Pacific coast of Mexico, and was felt at the Sandwich Isles, where the Kilanea volcano was set in motion almost at the same time that the sea-wave came in. But there can be no doubt whatever that, as in the case of the great Peruvian earthquake of August, 1868, the sea-wave had its origin not in the local subterranean disturbances, but in the great upheaval by which Iquique and other places were destroyed. We shall, no doubt, hear before long, as in that case, of the arrival of the great wave at the Samoa Isles, at the Japanese Archipelago, on the shores of New Zealand, Australia, and so forth. Now, the great circular wave which spread on May 10 last from the Peruvian shore as a centre athwart the entire Pacific was probably not felt by a single ship in the open sea, any more than the still vaster wave of the 13th and 14th of August, 1868, and for the same reason. With a height of some fifteen feet (or thirty feet vertical difference between crest and hollow), the wave had yet so gentle a slope that, though it rushed at the rate of three or four hundred miles an hour across the Pacific, the rise and fall of a ship upon its surface would be altogether imperceptible. The great sea-wave, as Mallet long since pointed out, consists, in the deep ocean, of "a long, low swell of enormous volume, having an equal slope before and behind, and that so gentle that it might pass under a ship without being noticed." And we are told, in fact, by a modern writer, that during the rush of the great sea-wave across the Pacific on August 13-14, 1868, though where the wave reached island shores it seemed as though the land were first sinking bodily into the ocean and then rising bodily out of it, "there was not one among the hundreds of vessels which were sailing upon the Pacific when it was traversed by the sea-wave in which any unusual motion was perceived."
How, then, it may be asked, can we suppose that a wave which was not perceived by those actually sailing upon the ocean traversed by it, could have been visible with suitable telescopic power from a distant planet? The very circumstance which rendered the rise and fall of ships upon the sea-waves of 1868 and of last May imperceptible, assures us that the progress of the wave would so have been visible. Besides its enormous range in length, for when it struck the Sandwich Isles its crest must have formed the arc of a great curve, having for radius the distance of sixty-three hundred miles, separating that group from Peru, the wave had great breadth, otherwise, its height being about thirty feet, the rapid advance of the wave would have caused a rapid rise and fall, instead of a slow motion only discernible along shore-lines. Probably the distance from valley to valley, on either side of the mighty crest of the wave, was not less than two hundred miles in the open sea. So far as mere dimensions, then, are concerned, the great wave would certainly have been visible from a planet placed as Venus is, when most favorably situated for observing the earth. To show this, it is only necessary to point out that Venus is then much nearer to us than Mars ever is, that the entire diameter of Mars is but about forty-five hundred miles, while the radius of the great wave, when it reached the Sandwich Isles, was fully six thousand miles, and that its probable breadth of two hundred miles very far exceeds the breadth of many of the well-known markings upon the planet Mars.
But it may be asked how the wave would become discernible at all, viewed, as it were, from above. How should an observer in Venus know that the highest part of the wave was thirty feet or so nearer to him than the hollow of the valleys on either side of it? The way in which the wave would become visible corresponds in some degree to the way in which those strange radiations which extend from several of the lunar craters are visible, though they have very little elevation, cast no perceptible shadows, and are many of them undiscernible when other lunar features are clearly seen, and become discernible only when those other features are scarcely visible at all. Under the sun's rays, the two opposite faces of the advancing waves would be differently illuminated. One face, a hundred miles broad, be it remembered, would catch the light more fully than the ocean as yet undisturbed, while the other would catch the light less fully. Thus the mighty arc of the wave would appear as a double arc, one-half of its breadth being bright, the other (relatively) dark. We do not say that the wave would be a very striking or obvious feature of the earth's disc as seen from Venus, but that it would be discernible under the same telescopic power which the Herschels, Lassell, Rosse, and others have applied to the celestial objects as seen from the earth, we have little doubt. If so, since not only would it be perceived as a new feature, but also its motion across the Pacific be traceable, and the transience of the phenomenon quickly recognized, it would afford observers on that planet the clearest evidence of the activity of subterranean forces within our earth. Those among the observers living on Venus who were not content merely to observe, but exercised also their reasoning faculties to determine the meaning of what they saw, would perceive that on or about August 13-14, 1868, and again on May 10 last, tremendous throes had shaken some portion of the southern half of that long double continent lying north and south which they have long since recognized on our globe; that the waters of the ocean had thus been mightily disturbed; and that a great wave, or rather a succession of several great waves, had swept across the largest of the terrestrial oceans. They would be able even; by noting the velocity and variations of velocity of the great wave, to determine the depth of the Pacific Ocean, and the manner according to which the depth varies in the neighborhood of different island groups. It is not altogether impossible, indeed, that what we have here described may actually have occurred, though on neither of the occasions when the Pacific has of late been swept by a sea-wave was Venus very suitably placed for observing our planet.
Apart from thoughts such as these, there is much in a phenomenon like this great sea-wave well worth considering. When we recognize in the subterranean forces of our earth an energy competent to disturb the entire surface of the Pacific, we perceive how vain are the fears of those who imagine that the earth's Vulcanian energies are very nearly exhausted. There is nothing to show that at any time of which geology affords evidence throes more mighty than those which have shaken Peru and Chili within the last half-century have disturbed any portion of the earth's frame. In former times indeed, when geologists were accustomed to regard the processes of an entire era as completed in a single throe, men might well believe that the earth had sunk into relative quiescence. But now that close study has enabled them to separate the effects of one process from those of another, to recognize — not in full perhaps, but in great degree — the influence of time as an important factor in geological development, they are able to make a juster comparison between past and present disturbances. The result is, that, although we cannot doubt that the earth is parting with the heat which is the source of its Vulcanian energies, we find every reason to believe that the loss of energy is taking place so slowly that the diminution during many generations is altogether imperceptible. As a modern writer has remarked, when we see that while mountain ranges were being upheaved or valleys depressed to their present position, race after race and type after type lived out on the earth the long lives which belong to races and to types, we recognize the great work which the earth's subterranean forces are still engaged upon. Even now continents are being slowly depressed or upheaved, even now mountain ranges are being raised to a different level, table-lands are being formed, great valleys are being gradually scooped out, old shore-lines shift their place, old soundings vary, the sea advances in one place and retires in another; on every side, nature's plastic hand is still at work, modelling and remodelling the earth, and making it constantly a fit abode for those who dwell upon it.