Pleasant Ways in Science

by Richard A. Proctor

On May 10th, 1876, a tremendous wave swept the Pacific Ocean from Peru northwards, westwards, and southwards, travelling at a rate many times greater than that of the swiftest express train. For reasons best known to themselves, writers in the newspapers have by almost common consent called this phenomenon a tidal-wave. But the tides had nothing to do with it. Unquestionably the wave resulted from the upheaval of the bed of the ocean in some part of that angle of the Pacific Ocean which is bounded by the shores of Peru and Chili. This region has long been celebrated for tremendous submarine and subterranean upheavals. The opinions of geologists and geographers have been divided as to the real origin of the disturbances by which at one time the land, at another time the sea, and at yet other times (oftener, in fact, than either of the others) both land and sea have been shaken as by some mighty imprisoned giant, struggling, like Prometheus, to cast from his limbs the mountain masses which hold them down. Some consider that the seat of the Vulcanian forces lies deep below that part of the chain of the Andes which lies at the apex of the angle just mentioned, and that the direction of their action varies according to the varying conditions under which the imprisoned gases find vent. Others consider that there are two if not several seats of subterranean activity. Yet others suppose that the real seat of disturbance lies beneath the ocean itself, a view which seems to find support in several phenomena of recent Peruvian earthquakes.

Although we have not full information concerning the great wave which in May, 1876, swept across the Pacific, and northwards and southwards along the shores of the two Americas, it may be interesting to consider some of the more striking features of this great disturbance of the so-called peaceful ocean, and to compare them with those which have characterized former disturbances of a similar kind. We may thus, perhaps, find some evidence by which an opinion may be formed as to the real seat of subterranean activity in this region.

At the outset it may be necessary to explain why I have asserted somewhat confidently that the tides have nothing whatever to do with this great oceanic wave. It is of course well known to every reader that the highest or spring tides occur always two or three days after new moon and after full moon, the lowest (or rather the tides having least range above and below the mean level) occurring two or three days after the first and third quarters of the lunar month. The sun and moon combine, indeed, to sway the ocean most strongly at full and new, while they pull contrariwise at the first and third quarters; but the full effect of their combined effort is only felt a few days later than when it is made, while the full effect of their opposition to each other, in diminishing the range of the oceanic oscillation, is also only felt after two or three days. Thus in May, 1876, the tidal wave had its greatest range on or about May 16, new moon occurring at half-past five on the morning of May 13; and the tidal wave had its least range on or about May 8, the moon passing her third quarter a little after eleven on the morning of May 4. Accordingly the disturbance which affected the waters of the Pacific so mightily on May 10, occurred two days after the lowest or neap tides, and five days before the highest or spring tides. Manifestly that was not a time when a tidal wave of exceptional height could be expected, or, indeed, could possibly occur. Such a wave as actually disturbed the Pacific on that day could not in any case have been produced by tidal action, even though the winds had assisted to their utmost, and all the circumstances which help to make high tides had combined—as the greatest proximity of moon to earth, the conjunction of moon and sun near the celestial equator, and (of course) the exact coincidence of the time of the tidal disturbance with that when the combined pull of the sun and moon is strongest. As, instead, the sun was nearly eighteen degrees from the equator, the moon more than nine, and as the moon was a full week’s motion from the part of her path where she is nearest to the earth, while, as we have seen, only two days had passed from the time of absolutely lowest tides, it will be seen how utterly unable the tidal-wave must have been on the day of the great disturbance to produce the effects presently to be described.

It may seem strange, in dealing with the case of a wave which apparently had its origin in or near Peru on May 9, to consider the behaviour of a volcano, distant 5000 miles from this region, a week before the disturbance took place. But although the coincidence may possibly have been accidental, yet in endeavouring to ascertain the true seat of disturbance we must overlook no evidence, however seemingly remote, which may throw light on that point; and as the sea-wave generated by the disturbance reached very quickly the distant region referred to, it is by no means unlikely that the subterranean excitement which the disturbance relieved may have manifested its effects beforehand at the same remote volcanic region. Be this as it may, it is certain that on May 1 the great crater of Kilauea, in the island of Hawaii, became active, and on the 4th severe shocks of earthquake were felt at the Volcano House. At three in the afternoon a jet of lava was thrown up to a height of about 100 feet, and afterwards some fifty jets came into action. Subsequently jets of steam issued along the line formed by a fissure four miles in length down the mountain-side. The disturbance lessened considerably on the 5th, and an observing party examined the crater. They found that a rounded hill, 700 feet in height, and 1400 feet in diameter, had been thrown up on the plain which forms the floor of the crater. Fire and scoria spouted up in various places.

Before rejecting utterly the belief that the activity thus exhibited in the Hawaii volcano had its origin in the same subterrene or submarine region as the Peruvian earthquake, we should remember that other regions scarcely less remote have been regarded as forming part of the same Vulcanian district. The violent earthquakes which occurred at New Madrid, in Missouri, in 1812, took place at the same time as the earthquake of Caraccas, the West Indian volcanoes being simultaneously active; and earthquakes had been felt in South Carolina for several months before the destruction of Caraccas and La Guayra. Now we have abundant evidence to show that the West Indian volcanoes are connected with the Peruvian and Chilian regions of Vulcanian energy, and the Chilian region is about as far from New Madrid as Arica in Peru from the Sandwich Isles.

It was not, however, until about half-past eight on the evening of May 9 that the Peruvian earthquake began. A severe shock, lasting from four to five minutes, was felt along the entire southern coast, even reaching Antofagasta. The shock was so severe that it was impossible, in many places, to stand upright. It was succeeded by several others of less intensity.

While the land was thus disturbed, the sea was observed to be gradually receding, a movement which former experiences have taught the Peruvians to regard with even more terror than the disturbance of the earth itself. The waters which had thus withdrawn, as if concentrating their energies to leap more fiercely on their prey, presently returned in a mighty wave, which swept past Callao, travelling southwards with fearful velocity, while in its train followed wave after wave, until no less than eight had taken their part in the work of destruction. At Mollendo the railway was torn up by the sea for a distance of 300 feet. A violent hurricane which set in afterwards from the south prevented all vessels from approaching, and unroofed most of the houses in the town. At Arica the people were busily engaged in preparing temporary fortifications to repel a threatened assault of the rebel ram Huiscar, at the moment when the roar of the earthquake was heard. The shocks here were very numerous, and caused immense damage in the town, the people flying to the Morro for safety. The sea was suddenly perceived to recede from the beach, and a wave from ten feet to fifteen feet in height rolled in upon the shore, carrying before it all that it met. Eight times was this assault of the ocean repeated. The earthquake had levelled to the ground a portion of the custom-house, the railway station, the submarine cable office, the hotel, the British Consulate, the steamship agency, and many private dwellings. Owing to the early hour of the evening, and the excitement attendant on the proposed attack of the Huiscar, every one was out and stirring; but the only loss of life which was reported was that of three little children who were overtaken by the water. The progress of the wave was only stopped at the foot of the hill on which the church stands, which point is further inland than that reached in August, 1868. Four miles of the embankment of the railway were swept away like sand before the wind. Locomotives, cars, and rails, were hurled about by the sea like so many playthings, and left in a tumbled mass of rubbish.

The account proceeds to say that the United States steamer Waters, stranded by the bore of 1868, was lifted up bodily by the wave at Arica, and floated two miles north of her former position. The reference is no doubt to the double-ender Watertree, not stranded by a bore (a term utterly inapplicable to any kind of sea-wave at Arica, where there is no large river), but carried in by the great wave which followed the earthquake of August 13. The description of the wave at Arica on that occasion should be compared with that of the wave of May, 1876. About twenty minutes after the first earth shock, the sea was seen to retire, as if about to leave the shores wholly dry; but presently its waters returned with tremendous force. A mighty wave, whose length seemed immeasurable, was seen advancing like a dark wall upon the unfortunate town, a large part of which was overwhelmed by it. Two ships, the Peruvian corvette America, and the American double-ender Watertree, were carried nearly half a mile to the north of Arica, beyond the railroad which runs to Tacna, and there left stranded high and dry. As the English vice-consul at Arica estimated the height of this enormous wave at fully fifty feet, it would not seem that the account of the wave of May, 1876, has been exaggerated, for a much less height is, as we have seen, attributed to it, though, as it carried the Watertree still further inland, it must have been higher. The small loss of life can be easily understood when we consider that the earthquake was not followed instantly by the sea-wave. Warned by the experience of the earthquake of 1868, which most of them must have remembered, the inhabitants sought safety on the higher grounds until the great wave and its successors had flowed in. We read that the damage done was greater than that caused by the previous calamity, the new buildings erected since 1868 being of a more costly and substantial class. Merchandise from the custom-house and stores was carried by the water to a point on the beach five miles distant.

At Iquique, in 1868, the great wave was estimated at fifty feet in height. We are told that it was black with the mud and slime of the sea bottom. “Those who witnessed its progress from the upper balconies of their houses, and presently saw its black mass rushing close beneath their feet, looked on their safety as a miracle. Many buildings were, indeed, washed away, and in the low-lying parts of the town there was a terrible loss of life.” In May, 1876, the greatest mischief at Iquique would seem to have been caused by the earthquake, not by the sea-wave, though this also was destructive in its own way. “Iquique,” we are told, “is in ruins. The movement was experienced there at the same time and with the same force [as at Arica]. Its duration was exactly four minutes and a third. It proceeded from the south-east, exactly from the direction of Ilaga.” The houses built of wood and cane tumbled down at the first attacks, lamps were broken, and the burning oil spread over and set fire to the ruins. Three companies of firemen, German, Italian, and Peruvian, were instantly at their posts, although it was difficult to maintain an upright position, shock following shock with dreadful rapidity. Nearly 400,000 quintals of nitrate in the stores at Iquique and the adjacent ports of Molle and Pisagua were destroyed. The British barque Caprera and a German barque sank, and all the coasting craft and small boats in the harbour were broken to pieces and drifted about in every direction.

At Chanavaya, a small town at the guano-loading dépôt known as Pabellon de Pica, only two houses were left standing out of four hundred. Here the earthquake shock was specially severe. In some places the earth opened in crevices seventeen yards deep and the whole surface of the ground was changed.