general tendency of subterranean movements, when their effects are
considered for a sufficient lapse of ages, is eminently beneficial,
and that they constitute an essential part of that mechanism by which
the integrity of the habitable surface is preserved. Why the working
of this same machinery should be attended with so much evil, is a
mystery far beyond the reach of our philosophy, and must probably
remain so until we are permitted to investigate, not our planet alone
and its inhabitants, but other parts of the moral and material universe
with which they may be connected. Could our survey embrace other
worlds, and the events, not of a few centuries only, but of periods
as indefinite as those with which geology renders us familiar, some
apparent contradictions might be reconciled, and some difficulties
would doubtless be cleared up. But even then, as our capacities are
finite, while the scheme of the universe must be infinite, both in time
and space, it is presumptuous to suppose that all sources of doubt and
perplexity would ever be removed. On the contrary, they might, perhaps,
go on augmenting in number although our confidence in the wisdom of the
plan of nature might increase at the same time; for it has been justly
said’ (by Sir Humphry Davy) ‘that the greater the circle of light, the
greater the boundary of darkness by which it is surrounded.’
(From the _Cornhill Magazine_, March 1868.)
_THE EARTHQUAKE IN PERU._
The intelligence published last Saturday (see date of article) is
sufficient to prove that the great earthquake which has devastated
Peru fully equalled, if it did not surpass, the most terrible
catastrophes which have ever befallen that country. It presents, too,
all the features which have hitherto characterised earthquakes in this
neighbourhood. These are well worthy of careful study, and appear to
have an important bearing on the modern theory of earthquakes.
It has been commonly held that the seat of disturbance in the
earthquakes which have shaken the country west of the Andes has lain
always at some point or other beneath that range of mountains. The
fact that several large volcanoes are found in the Cordilleras has
seemed confirmatory of this view. The account we have also of the great
earthquake at Riobamba in 1797, seems only explicable by supposing
that the seat of disturbance lay almost immediately beneath that city.
The inhabitants were flung vertically upwards into the air, and to
such a height that Humboldt found the skeletons of many of them on the
summit of the hill La Culca, on the farther side of the small river on
which Riobamba is built. The ruins of many houses were also flung to
the same spot. Here, therefore, was evidence of that vertical (or, as
Humboldt expresses it, explosive) force which is only to be looked for
immediately above the centre of concussion.
Yet the consideration of the evidence afforded by the news just
published seems at first sight somewhat opposed to this view, and
to point rather to a seat of disturbance lying considerably to the
west of the Peruvian shores. ‘At Chala,’ says our informant, ‘the sea
receded, and a wave rose fifty feet, and returned, spreading into the
town, a distance of about a thousand feet. Three successive times
everything within range was swept away, followed by twelve shocks of
earthquake, lasting from three seconds to two minutes.’ The arrival
of great sea-waves before the land-shocks were felt, seems decisively
to indicate that the seat of disturbance lay beneath the ocean, and
not beneath the land. I am disposed to believe, however, that in
the confusion of mind naturally resulting from the occurrence of so
terrible a catastrophe, the sequence of events may not have been very
closely attended to, for in other places the arrival of the great
sea-wave is distinctly described as following the occurrence of the
earth-shock. At Arica, for example, a considerable interval would
seem to have elapsed before the terrible sea-wave, which has always
characterised Peruvian earthquakes, poured in upon the town. The agent
of the Pacific Steam Navigation Company, whose house had been destroyed
by the earth-shock, saw the great sea-wave while he was flying towards
the hills. He writes:—’While passing towards the hills, with the earth
shaking, a great cry went up to heaven. The sea had retired. On
clearing the town, I looked back and saw that the vessels were being
carried irresistibly seawards. In a few minutes the sea stopped, and
then arose a mighty wave fifty feet high, and came in with a fearful
rush, carrying everything before it in terrible majesty. The whole of
the shipping came back, speeding towards inevitable doom. In a few
minutes all was completed—every vessel was either on shore or bottom
upwards.’ This, then, was undoubtedly the great sea-wave, as compared
with the minor waves of disturbance which characterise all earthquakes
near the shores of the ocean.
One remarkable feature in this terrible earthquake is the enormous
range of country affected by it. From Quito southwards as far as
Iquique—or, in other words, for a distance considerably exceeding a
full third part of the whole length of the South American Andes—the
shock was felt with the most terrible distinctness. We have yet to
learn how much farther to the north and south, and how far inland on
the eastern slopes of the Andes, the shock was experienced. But there
can be little doubt that the disturbed country was equal to at least a
fourth of Europe.
The portion of the Andes thus disturbed seems to be distinct from the
part to which the great Chilian earthquakes belong. The difference in
character between the Peruvian and Chilian earthquakes is a singular
and interesting phenomenon. The difference corresponds to a feature
long since pointed out by Sir Charles Lyell,—the alternation, on a
grand scale, of districts of active with those of extinct volcanoes.
It is said that in Chili a year scarcely ever passes without shocks of
earthquake being felt; in certain regions, not even a month. A similar
persistence of earthquake-disturbance characterises Peru. Yet, although
both districts are shaken in this manner, there seems to be distinct
evidence of alternating disturbance as respects the occurrence of
great earthquakes. Thus in 1797 took place the terrible earthquake of
Riobamba. Then, thirty years later, a series of great earthquakes shook
Chili, permanently elevating the whole line of coast to the height of
several feet. Now, again, after another interval of about thirty years,
the Andes are disturbed by a great earthquake, and this time it is the
Peruvian Andes which experience the shock. Between Chili and Peru there
is a space upwards of five hundred miles long, in which no volcanic
action has been observed. Singularly enough, this very portion of the
Andes, to which one would imagine the Peruvians and Chilians would fly
as to a region of safety, is the part most thinly inhabited, insomuch
that, as Von Buch observes, it is in some places entirely deserted.
Near Quito the trembling of the earth is almost incessant, according
to M. Boussingault. He considers that the frequency of the movement
is due rather to the continual falling in of masses of rock which
have been fractured in recent earthquakes, than to the persistence of
subterranean action. He adds that the height of several mountains in
the Andes has diminished in modern times. He refers, doubtless, to the
Peruvian and Columbian Andes, and not to the Chilian. In the latter
portion of the range there must be a continual increase of height,
since each earthquake in Chili has produced a perceptible recession of
the sea. Darwin, indeed, relates that near Valparaiso he saw beds of
seashells belonging to recent species at a height of about a quarter of
a mile above the present sea-level; and he concluded that the land had
been raised to this height by a series of such small elevations as were
observed to have taken place during the earthquakes of 1822, 1835, and
1837. That a contrary process should be going on in Peru, confirms the
idea that a sort of undulatory or balancing motion is taking place—one
long stretch of the Cordilleras rising while another is sinking. A
tradition prevails among the Indians of Lican that the mountain called
L’Altar, or Cassac Urcu—which means ‘the chief’—was once the highest of
the sub-equatorial Andes, being higher even than Chimborazo; but, adds
the tradition, in the reign of Quainia Abomatha, before the discovery
of America, a prodigious eruption took place, which lasted no less
than eight years, and brought down the summit of the mountain. M.
Boussingault states that the fragments of trachyte which once formed
the summit of this celebrated mountain are now spread over the plain.
At present Cotopaxi is the loftiest volcano of the Cordilleras, its
height being no less than 18,858 feet. No mountain has ever been the
seat of such terrible and destructive eruptions as those which have
burst forth from Cotopaxi. The intensity of the heat which prevails
during eruption will be readily gathered from the circumstance that in
January 1803 the enormous bed of snow which usually covers the cone of
the volcano was dissolved in a single night.
It would seem that the Mexican volcanoes also belong to the same region
of disturbance. Near the Isthmus of Panama the great Cordillera of the
Andes is reduced to the height of about 800 feet, and beyond begins
the continuation of the volcanic chain in Central America and Mexico.
Nor are the volcanoes of the West Indian or Caribbee Islands wholly
disconnected with the region of disturbance in Southern America. And
it is rather singular that even the earthquakes which have occurred in
the valley of the Mississippi seem to be connected with the West Indian
and South American volcanic region. The violent earthquakes which
took place at New Madrid in 1812 occurred at exactly the same time as
the earthquake of Paranas, ‘so that it is possible,’ says Sir Charles
Lyell, ‘that these two points are part of one volcanic region.’
(From the _Daily News_, September 18, 1868.)
_THE GREATEST SEA-WAVE EVER KNOWN._
On August 13, 1868, one of the most terrible calamities which has ever
visited a people befell the unfortunate inhabitants of Peru. In that
land earthquakes are nearly as common as rain-storms are with us; and
shocks by which whole cities are changed into a heap of ruins are by
no means infrequent. Yet even in Peru, ‘the land of earthquakes,’ as
Humboldt has termed it, no such catastrophe as that of August 1868 had
occurred within the memory of man. It was not one city which was laid
in ruins, but a whole empire. Those who perished were counted by tens
of thousands, while the property destroyed by the earthquake was valued
at millions of pounds sterling.
Although so many months have passed since this terrible calamity took
place, scientific men have been busily engaged until quite recently
in endeavouring to ascertain the real significance of the various
events which were observed during and after the occurrence of the
earthquake. The geographers of Germany have taken a special interest
in interpreting the evidence afforded by this great manifestation of
nature’s powers. Two papers have been written recently on the great
earthquake of August 13, 1868, one by Professor Von Hochstetter, the
other by Herr Von Tschudi, which present an interesting account of the
various effects, by land and by sea, which resulted from the tremendous
upheaving force to which the western flanks of the Peruvian Andes were
subjected on that day. The effects on land, although surprising and
terrible, yet only differ in degree from those which have been observed
in other earthquakes. But the progress of the great sea-wave which
was generated by the upheaval of the Peruvian shores and propagated
over the whole of the Pacific Ocean differs altogether from any
earthquake-phenomena before observed. Other earthquakes have indeed
been followed by oceanic disturbances; but these have been accompanied
by terrestrial motions, so as to suggest the idea that they had been
caused by the motion of the sea-bottom, or of the neighbouring land.
In no instance has it ever before been known that a well-marked wave
of enormous proportions should have been propagated over the largest
ocean-tract on our globe, by an earth-shock whose direct action was
limited to a relatively small region, and that region not situated in
the centre, but on one side of the wide area traversed by the wave.
I propose to give a brief sketch of the history of this enormous
sea-wave. In the first place, however, it may be well to remind the
reader of a few of the more prominent features of the great shock to
which this wave owed its origin.
It was at Arequipa, at the foot of the lofty volcanic mountain
Misti, that the most terrible effects of the great earthquake
were experienced. Within historic times Misti has poured forth no
lava-streams; but that the volcano is not extinct is clearly shown by
the fact that in 1542 an enormous mass of dust and ashes was vomited
forth from its crater. On August 13, 1868, Misti showed no signs of
being disturbed. So far as their volcanic neighbour was concerned,
the 44,000 inhabitants of Arequipa had no reason to anticipate the
catastrophe which presently befell them. At five minutes past five an
earthquake shock was experienced, which, though severe, seems to have
worked little mischief. Half a minute later, however, a terrible noise
was heard beneath the earth; a second shock more violent than the first
was felt; and then began the swaying motion, gradually increasing in
intensity. In the course of the first minute this motion had become so
violent that the inhabitants ran in terror out of their houses into
the streets and squares. In the next two minutes the swaying movement
had so increased that the more lightly-built houses were cast to the
ground, and the flying people could scarcely keep their feet. ‘And
now,’ says Von Tschudi, ‘there followed during two or three minutes a
terrible scene. The swaying motion which had hitherto prevailed changed
into fierce vertical upheaval. The subterranean roaring increased
in the most terrifying manner: then were heard the heart-piercing
shrieks of the wretched people, the bursting of walls, the crashing
fall of houses and churches, while over all rolled thick clouds of a
yellowish-black dust, which, had they been poured forth many minutes
longer, would have suffocated thousands.’ Although the shock had lasted
but a few minutes, the whole town was destroyed. Not one building
remained uninjured, and there were few which did not lie in shapeless
heaps of ruins.
At Tacna and Arica, the earth-shock was less severe, but strange and
terrible phenomena followed it. At the former place a circumstance
occurred, the cause and nature of which yet remain a mystery. About
three hours after the earthquake—in other words, at about eight o’clock
in the evening—an intensely brilliant light made its appearance above
the neighbouring mountains. It lasted for fully half an hour, and has
been ascribed to the eruption of some as yet unknown volcano.
At Arica the sea-wave produced even more destructive effects than had
been caused by the earthquake. 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 United States ‘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. This enormous wave
was considered by the English vice-consul at Arica to have been fully
fifty feet in height.
At Chala, three such waves swept in after the first shocks of
earthquake. They overflowed nearly the whole of the town, the sea
passing more than half a mile beyond its usual limits.
At Islay and Iquique similar phenomena were manifested. At the former
town the sea flowed in no less than five times, and each time with
greater force. Afterwards the motion gradually diminished, but even an
hour and a half after the commencement of this strange disturbance, the
waves still ran forty feet above the ordinary level. At Iquique, the
people beheld the inrushing wave whilst it was still a great way off. A
dark blue mass of water, some fifty feet in height, was seen sweeping
in upon the town with inconceivable rapidity. An island lying before
the harbour was completely submerged by the great wave, which still
came rushing on, black with the mud and slime it had swept from 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. After passing far inland the wave slowly
returned seawards, and strangely enough, the sea, which elsewhere
heaved and tossed for hours after the first great wave had swept over
it, here came soon to rest.
At Callao a yet more singular instance was afforded of the effect
which circumstances may have upon the motion of the sea after a
great earthquake has disturbed it. In former earthquakes Callao has
suffered terribly from the effects of the great sea-wave. In fact,
on two occasions the whole town has been destroyed, and nearly all
its inhabitants have been drowned, through the inrush of precisely
such waves as flowed into the ports of Arica and Chala. But upon
this occasion the centre of subterranean disturbance must have been
so situated that either the wave was diverted from Callao, or more
probably two waves reached Callao from different sources and at
different times, so that the two undulations partly counteracted each
other. Certain it is that, although the water retreated strangely from
the coast near Callao, insomuch that a wide tract of the sea-bottom was
uncovered, there was no inrushing wave comparable with those described
above. The sea afterwards rose and fell in an irregular manner, a
circumstance confirming the supposition that the disturbance was caused
by two distinct oscillations. Six hours after the occurrence of the
earth-shock, the double oscillations seem for a while to have worked
themselves into unison, for at this time three considerable waves
rolled in upon the town. But clearly these waves must not be compared
with those which in other instances had made their appearance within
half an hour of the earth-throes. There is little reason to doubt that
if the separate oscillations had reinforced each other earlier, Callao
would have been completely destroyed. As it was, a considerable amount
of mischief was effected; but the motion of the sea presently became
irregular again, and so continued until the morning of August 14th,
when it began to ebb with some regularity. But during the 14th there
were occasional renewals of the irregular motion, and several days
elapsed before the regular ebb and flow of the sea were resumed.
Such were among the phenomena presented in the region where the
earthquake itself was felt. It will be seen at once that within this
region, or rather along that portion of the sea-coast which falls
within the central region of disturbance, the true character of the
sea-wave generated by the earthquake could not be recognised. If a rock
fall from a lofty cliff into a comparatively shallow sea, the water
around the place where the rock has fallen is disturbed in an irregular
manner. The sea seems at one place to leap up and down; elsewhere one
wave seems to beat against another, and the sharpest eye can detect
no law in the motion of the seething waters. But presently, outside
the scene of disturbance, a circular wave is seen to form, and if the
motion of this wave be watched, it is seen to present the most striking
contrast to the turmoil and confusion at its centre. It sweeps onwards
and outwards in a regular undulation. Gradually it loses its circular
figure (unless the sea-bottom happens to be unusually level), showing
that although its motion is everywhere regular, it is not everywhere
equally swift. A wave of this sort, though incomparably vaster, swept
swiftly away on every side from the scene of the great earthquake near
the Peruvian Andes. It has been calculated that the width of this wave
varied from one million to five million feet, or roughly, from 200
to 1,000 miles, while, when in mid-Pacific, the length of the wave,
measured along its summit in a widely-curved path from one side to
another of the great ocean, cannot have been less than 8,000 miles.
We cannot tell how deep-seated was the centre of subterranean action;
but there can be no doubt it was very deep indeed, because otherwise
the shock felt in towns separated from each other by hundreds of miles
could not have been so nearly contemporaneous. Therefore the portion of
the earth’s crust upheaved must have been enormous, for the length of
the region where the direct effects of the earthquake were perceived is
estimated by Professor Von Hochstetter at no less than 240 miles. The
breadth of the region is unknown, because on one side the slope of the
Andes and on the other the ocean concealed the motion of the earth’s
crust.
The great ocean wave swept, as I have said, in all directions around
the scene of the earth-throe. Over a large part of its course its
passage was unnoted, because in the open sea the effects even of so
vast an undulation could not be perceived. A ship would slowly rise as
the crest of the great wave passed under her, and then as slowly sink
again. This may seem strange, at first sight, when it is remembered
that in reality the great sea-wave we are considering swept at the rate
of three or four hundred sea-miles an hour over the larger part of the
Pacific. But when the true character of ocean-waves is understood, when
it is remembered that there is no transference of the water itself at
this enormous rate, but simply a transmission of motion (precisely as
when in a high wind waves sweep rapidly over a corn-field, while yet
each cornstalk remains fixed in the ground), it will be seen that the
effects of the great sea-wave could only be perceived near the shore.
Even there, as we shall presently see, there was much to convey the
impression that the land itself was rising and falling rather than
that the deep was moved. But among the hundreds of ships which were
sailing upon the Pacific when its length and breadth were traversed by
the great sea-wave, there was not one in which any unusual motion was
perceived.
In somewhat less than three hours after the occurrence of the
earthquake, the ocean-wave inundated the port of Coquimbo, on the
Chilian seaboard, some 800 miles from Arica. An hour or so later it
had reached Constitucion, 450 miles farther south; and here for some
three hours the sea rose and fell with strange violence. Farther south,
along the shore of Chili, even to the island of Chiloe, the shore-wave
travelled, though with continually diminishing force, owing doubtless
to the resistance which the irregularities of the shore opposed to its
progress.
The northerly shore-wave seems to have been more considerable; and
a moment’s study of a chart of the two Americas will show that this
circumstance is highly significant. When we remember that the principal
effects of the land-shock were experienced within that angle which
the Peruvian Andes form with the long north-and-south line of the
Chilian and Bolivian Andes, we see at once that, had the centre of the
subterranean action been near the scene where the most destructive
effects were perceived, no sea-wave, or but a small one, could have
been sent towards the shores of North America. The projecting shores of
northern Peru and Ecuador could not have failed to divert the sea-wave
towards the west; and though a reflected wave might have reached
California, it would only have been after a considerable interval of
time, and with dimensions much less than those of the sea-wave which
travelled southwards. When we see that, on the contrary, a wave of even
greater proportions travelled towards the shores of North America,
we seem forced to the conclusion that the centre of the subterranean
action must have been so far to the west that the sea-wave generated by
it had a free course to the shores of California.