the shores of Southern California, rising upwards of sixty feet above
the ordinary sea-level, was absolutely the most imposing of all the
indirect effects of the great earthquake. When we consider that
even in San Pedro Bay, fully five thousand miles from the centre of
disturbance, a wave twice the height of an ordinary house rolled in
with unspeakable violence only a few hours after the occurrence of
the earth-throe, we are most strikingly impressed with the tremendous
energy of the earth’s movement.
Turning to the open ocean, let us track the great wave on its course
past the multitudinous islands which dot the surface of the great
Pacific.
The inhabitants of the Sandwich Islands, which lie about 6,300 miles
from Arica, might have imagined themselves safe from any effects
which could be produced by an earthquake taking place so far away
from them. But on the night between August 13 and 14, the sea around
this island-group rose in a surprising manner, insomuch that many
thought the islands were sinking and would shortly subside altogether
beneath the waves. Some of the smaller islands, indeed, were for a
time completely submerged. Before long, however, the sea fell again,
and as it did so the observers ‘found it impossible to resist the
impression that the islands were rising bodily out of the water.’ For
no less than three days this strange oscillation of the sea continued
to be experienced, the most remarkable ebbs and floods being noticed at
Honolulu, on the island of Woahoo.
But the sea-wave swept onwards far beyond these islands.
At Yokohama, in Japan, more than 10,500 miles from Arica, an enormous
wave poured in on August 14, but at what hour we have no satisfactory
record. So far as distance is concerned, this wave affords most
surprising evidence of the stupendous nature of the disturbance to
which the waters of the Pacific Ocean had been subjected. The whole
circumference of the earth is but 25,000 miles, so that this wave had
travelled over a distance considerably greater than two-fifths of the
earth’s circumference. A distance which the swiftest of our ships could
not traverse in less than five or six weeks had been swept over by this
enormous undulation in the course of a few hours.
More complete details reach us from the Southern Pacific.
Shortly before midnight the Marquesas Isles and the low-lying Tuamotu
group were visited by the great wave, and some of these islands were
completely submerged by it. The lonely Opara Isle, where the steamers
which run between Panama and New Zealand have their coaling station,
was visited at about half-past eleven in the evening by a billow which
swept away a portion of the coal depôt. Afterwards great waves came
rolling in at intervals of about twenty minutes, and several days
elapsed before the sea resumed its ordinary ebb and flow.
It was not until about half-past two on the morning of August 14, that
the Samoa Isles (sometimes called the Navigator Islands) were visited
by the great wave. The watchmen startled the inhabitants from their
sleep by the cry that the sea was about to overwhelm them; and already,
when the terrified people rushed from their houses, the sea was found
to have risen far above the highest watermark. But it presently began
to sink again, and then commenced a series of oscillations, which
lasted for several days and were of a very remarkable nature. Once in
every quarter of an hour the sea rose and fell, but it was noticed
that it rose twice as rapidly as it sank. This peculiarity is well
worth remarking. The eminent physicist Mallet speaks thus (I follow
Lyell’s quotation) about the waves which traverse an open sea: ‘The
great sea-wave, advancing at the rate of several miles in a minute,
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. But when it reaches the
edge of soundings its front slope becomes short and steep, while its
rear slope is long and gentle.’ On the shores visited by such a wave,
the sea would appear to rise more rapidly than it sank. We have seen
that this happened on the shores of the Samoan group, and therefore
the way in which the sea rose and fell on the days following the great
earthquake gave significant evidence of the nature of the sea-bottom in
the neighbourhood of these islands. As the change of the great wave’s
figure could not have been quickly communicated, we may conclude with
certainty that the Samoan Islands are the summits of lofty mountains,
whose sloping sides extend far towards the east.
This conclusion affords interesting evidence of the necessity of
observing even the seemingly trifling details of important phenomena.
The wave which visited the New Zealand Isles was altogether different
in character, affording a noteworthy illustration of another remark
of Mallet’s. He says that where the sea-bottom slopes in such a way
that there is water of some depth close in-shore, the great wave may
roll in and do little damage; and we have seen that so it happened in
the case of the Samoan Islands. But he adds, that ‘where the shore
is shelving, there will be first a retreat of the water, and then the
wave will break upon the beach and roll far in upon the land.’ This is
precisely what happened when the great wave reached the eastern shores
of New Zealand, which are known to shelve down to very shallow water,
continuing far away to sea towards the east:—
At about half-past three on the morning of August 14 the water began to
retreat in a singular manner from the Port of Lyttelton, on the eastern
shores of the southernmost of the New Zealand Islands. At length the
whole port was left entirely dry, and so remained for about twenty
minutes. Then the water was seen returning like a wall of foam ten
or twelve feet in height, which rushed with a tremendous noise upon
the port and town. Towards five o’clock the water again retired, very
slowly as before, not reaching its lowest ebb until six. An hour later,
a second huge wave inundated the port. Four times the sea retired and
returned with great power at intervals of about two hours. Afterwards
the oscillation of the water was less considerable, but it had not
wholly ceased until August 17, and only on the 18th did the regular ebb
and flow of the tide recommence.
Around the Samoan group the water rose and fell once in every fifteen
minutes, while on the shores of New Zealand each oscillation lasted
no less than two hours. Doubtless the different depths of water,
the irregular conformation of the island groups, and other like
circumstances, were principally concerned in producing these singular
variations. Yet they do not seem fully sufficient to account for so
wide a range of difference. Possibly a cause yet unnoticed may have
had something to do with the peculiarity. In waves of such enormous
extent, it would be quite impossible to determine whether the course of
the wave-motion was directed full upon a line of shore or more or less
obliquely. It is clear that in the former case the waves would seem to
follow each other more swiftly than in the latter, even though there
were no difference in their velocity.
Far on beyond the shores of New Zealand the great wave coursed,
reaching at length the coast of Australia. At dawn of August 14,
Moreton Bay was visited by five well-marked waves. At Newcastle, on
the Hunter River, the sea rose and fell several times in a remarkable
manner, the oscillatory motion commencing at half-past six in the
morning. But the most significant evidence of the extent to which
the sea-wave travelled in this direction was afforded at Port Fairy,
Belfast, South Victoria. Here the oscillation of the water was
distinctly perceived at midday on August 14; and yet, to reach this
point, the sea-wave must not only have travelled on a circuitous course
nearly equal in length to half the circumference of the earth, but
must have passed through Bass’s Straits, between Australia and Van
Diemen’s Land, and so have lost a considerable portion of its force and
dimensions.
When we remember that had not the effects of the earth-shock been
limited by the shores of South America, a wave of disturbance equal
in extent to that which travelled westward would have swept towards
the east, we see that the force of the shock was sufficient to have
disturbed the waters of an ocean covering the whole surface of the
earth. For the sea-waves which reached Yokohama in one direction and
Port Fairy in another had each traversed a distance nearly equal to
half the earth’s circumference; so that if the surface of the earth
were all sea, waves setting out in opposite directions from the centre
of disturbance would have met each other at the antipodes of their
starting-point.
It is impossible to contemplate the effects which followed the great
earthquake—the passage of a sea-wave of enormous volume over fully
one-third of the earth’s surface, and the force with which, at the
farthermost limits of its range, the wave rolled in upon shores more
than 10,000 miles from its starting-place—without feeling that those
geologists are right who deny that the subterranean forces of the
earth are diminishing in intensity. It may be difficult, perhaps,
to look on the effects which are ascribed to ancient earth-throes
without imagining for a while that the power of modern earthquakes is
altogether less. But when we consider fairly the share which time had
in those ancient processes of change, when we see that while mountain
ranges were being upheaved or valleys depressed to their present
position, race after race and type after type appeared on the earth,
and lived out the long lives which belong to races and to types, we
are recalled to the remembrance of 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 new level, table-lands are in process of formation,
and great valleys are being gradually scooped out. It may need an
occasional outburst such as the earthquake of August 1868 to remind
us that great forces are at work beneath the earth’s surface. But, in
reality, the signs of change have long been noted. 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 at work
modelling and remodelling the earth, in order that it may always be a
fit abode for those who are to dwell upon it.
(From _Fraser’s Magazine_, July 1870.)
_THE USEFULNESS OF EARTHQUAKES._
We have lately had fearful evidence of the energy of the earth’s
internal forces. A vibration which, when considered with reference
to the dimensions of the earth’s globe, may be spoken of as an
indefinitely minute quivering limited to an insignificant area, has
sufficed to destroy the cities and villages of whole provinces,
to cause the death of thousands of human beings, and to effect a
destruction of property which must be estimated by millions of pounds
sterling. Such a catastrophe as this serves indeed to show how poor
and weak a creature man is in presence of the grand workings of Nature.
The mere throes which accompany her unseen subterranean efforts suffice
to crumble man’s strongest buildings in a moment into dust, while the
unfortunate inhabitants are either crushed to death among the ruins,
or forced to remain shuddering spectators of the destruction of their
homes.
At first sight it may seem paradoxical to assert that earthquakes,
fearfully destructive as they have so often proved, are yet essentially
preservative and restorative phenomena; yet this is strictly the
case. Had no earthquakes taken place in old times, man would not now
be living on the face of the earth; if no earthquakes were to take
place in future, the term of man’s existence would be limited within
a range of time far less than that to which it seems likely, in all
probability, to be extended.
If the solid substance of the earth formed a perfect sphere in
ante-geologic times—that is, in ages preceding those to which our
present geologic studies extend—there can be no doubt that there was
then no visible land above the surface of the water; the ocean must
have formed a uniformly deep covering to the submerged surface of
the solid globe. In this state of things, nothing but the earth’s
subterranean forces could tend to the production of continents and
islands. Let me be understood. I am not referring to the possibility or
impossibility that lands and seas should suddenly have assumed their
present figure without convulsion of any sort; this _might_ have
happened, since the Creator of all things can doubtless modify all
things according to His will; I merely say that, assuming that in the
beginning, as now, He permitted all things to work according to the
laws He has appointed, then, undoubtedly, the submerged earth must have
risen above the sea by the action of those very forms of force which
produce the earthquake in our own times.
However this may be, it is quite certain that when once continents
and lands had been formed, there immediately began a struggle between
destructive and restorative (rather, perhaps, than preservative) forces.
The great enemy of the land is water, and water works the destruction
of the land in two principal ways.
In the first place the sea tends to destroy the land by beating on its
shores, and thus continually washing it away. It may seem at first
sight that this process must necessarily be a slow one; in fact, many
may be disposed to say that it is certainly a slow process, since
we see that it does not alter the forms of continents and islands
perceptibly in long intervals of time. But, as a matter of fact, we
have never had an opportunity of estimating the full effects of this
cause, since its action is continually being checked by the restorative
forces we shall presently have to consider. Were it not thus checked,
there can be little doubt that its effects would be cumulative; for the
longer the process continued—that is, the more the land was beaten
away—the higher would the sea rise, and the greater power would it have
to effect the destruction of the remaining land.
I proceed to give a few instances of the sea’s power of effecting
the rapid destruction of the land when nothing happens to interfere
with the local action—premising, that this effect is altogether
insignificant in comparison with that which would take place, even
in that particular spot, if the sea’s action were _everywhere_ left
unchecked.
The Shetland Isles are composed of substances which seem, of all
others, best fitted to resist the disintegrating forces of the
sea—namely, granite, gneiss, mica-slate, serpentine, greenstone, and
many other forms of rock: yet, exposed as these islands are to the
uncontrolled violence of the Atlantic Ocean, they are undergoing
a process of destruction which, even within historical times, has
produced very noteworthy changes. ‘Steep cliffs are hollowed out,’
says Sir Charles Lyell, ‘into deep caves and lofty arches; and almost
every promontory ends in a cluster of rocks imitating the forms of
columns, pinnacles, and obelisks.’ Speaking of one of the islands of
this group, Dr. Hibbert says: ‘The isle of Stennes presents a scene
of unequalled desolation. In stormy winters, large blocks of stone
are overturned, or are removed from their native beds, and hurried to
a distance almost incredible. In the winter of 1802, a tabular mass,
eight feet two inches by seven feet, and five feet one inch thick, was
dislodged from its bed, and carried to a distance of from eighty to
ninety feet. In other parts of the Shetland Isles, where the sea has
encountered less solid materials, the work of destruction has proceeded
yet more effectively. In Roeness, for example, the sea has wrought
its way so fiercely that a large cavernous aperture 250 feet long has
been hollowed out. But the most sublime scene,’ says Dr. Hibbert, ‘is
where a mural pile of porphyry, escaping the process of disintegration
that is devastating the coast, appears to have been left as a sort of
rampart against the inroads of the ocean. The Atlantic, when provoked
by wintry gales, batters against it with all the force of real
artillery; and the waves, in their repeated assaults, have at length
forced for themselves an entrance. This breach, named the Grind of the
Navir, is widened every winter by the overwhelming surge that, finding
a passage through it, separates large stones from its sides, and forces
them to a distance of no less than 180 feet. In two or three spots,
the fragments which have been detached are brought together in immense
heaps, that appear as an accumulation of cubical masses, the product of
some quarry.’
Let us next turn to a portion of the coast-line of Great Britain
which is neither defended, on the one hand, by barriers of rock, nor
attacked, on the other, by the full fury of the Atlantic currents.
Along the whole coast of Yorkshire we find evidences of a continual
process of dilapidation. Between the projecting headland of
Flamborough and Spurn Point (the coast of Holderness) the waste is
particularly rapid. Many spots, which are now mere sandbanks, are
marked in the old maps of Yorkshire as the sites of ancient towns and
villages. Speaking of Hyde (one of these), Pennant says: ‘Only the
tradition is left of this town.’ Owthorne and its church have been for
the most part destroyed, as also Auburn, Hartburn, and Kilnsea. Mr.
Phillips, in his ‘Geology of Yorkshire,’ states that not unreasonable
fears are entertained that, at some future time, Spurn Point itself
will become an island, or be wholly washed away, and then the ocean,
entering into the estuary of the Humber, will cause great devastation.
Pennant states that ‘several places, once towns of note upon the
Humber, are now only recorded in history; and Ravensperg was at one
time a rival of Hull, and a port so very considerable in 1332, that
Edward Baliol and the confederate English barons sailed from hence to
invade Scotland; and Henry IV., in 1399, made choice of this port to
land at, to effect the deposal of Richard II.; yet the whole of this
has since been devoured by the merciless ocean; extensive sands, dry
at low water, are to be seen in their stead.’ The same writer also
describes Spurn Point as shaped like a sickle, and the land to the
north, he says, was ‘perpetually preyed on by the fury of the German
Sea, which devours whole acres at a time.’
The decay of the shores of Norfolk and Suffolk is also remarkably
rapid. Sir Charles Lyell relates some facts which throw an interesting
light on the ravages which the sea commits upon the land here. It was
computed that when a certain inn was built at Sherringham, seventy
years would pass before the sea could reach the spot: ‘the mean loss
of land being calculated from previous observations to be somewhat
less than one yard annually.’ But no allowance had been made for the
fact that the ground sloped _from_ the sea. In consequence of this
peculiarity, the waste became greater and greater every year as the
cliff grew lower. ‘Between the years 1824 and 1829, no less than
seventeen yards were swept away;’ and when Sir Charles Lyell saw the
place, only a small garden was left between the building and the
sea. I need hardly add that all vestiges of the inn have long since
disappeared. Lyell also relates that, in 1829, there was a depth of
water sufficient to float a frigate at a point where, less than half a
century before, there stood a cliff fifty feet high with houses upon it.
I have selected these portions of the coast of Great Britain, not
because the destruction of our shores is greater here than elsewhere,
but as serving to illustrate processes of waste and demolition which
are going on around all the shores, not merely of Great Britain, but
of every country on the face of the earth. Here and there, as I have
said, there are instances in which a contrary process seems to be in
action. Low-lying banks and shoals are formed—sometimes along stretches
of coast extending for a considerable distance. But when we consider
these formations closely, we find that they rather afford evidence of
the energy of the destructive forces to which the land is subject
than promise to make up for the land which has been swept away. In the
first place, every part of these banks consists of the debris of other
coasts. Now we cannot doubt that of earth which is washed away from
our shores, by far the larger part finds its way to the bottom of the
deep seas; a small proportion only can be brought (by some peculiarity
in the distribution of ocean-currents, or in the progress of the
tidal wave) to aid in the formation of shoals and banks. The larger,
therefore, such shoals and banks may be, the larger must be the amount
of land which has been washed away never to reappear. And although
banks and shoals of this sort grow year by year larger and larger, yet
(unless added to artificially) they continue always either beneath
the surface of the water in the case of shoals, or but very slightly
raised above the surface. Now, if we suppose the destruction of land
to proceed unchecked, it is manifest that at some period, however
remote, the formation of shoals and banks must come to an end, owing
to the continual diminution of the land from the demolition of which
they derive their substance. In the meantime, the bed of the sea would
be continually filling up, the level of the sea would be continually
rising, and thus the banks would be either wholly submerged through the
effect of this cause alone, or they would have so slight an elevation
above the sea-level that they would offer little resistance to the
destructive effects of the sea, which would then have no other land to
act upon.
But we have yet to consider the second principal cause of the wasting
away of the land. The cause we have just been dealing with acts upon
the shores or outlines of islands and continents; the one we have now
to consider acts upon their interior. Many, perhaps, would hardly
suppose that the fall of rain upon the land could have any appreciable
influence in the demolition of continents; but, as a matter of fact,
there are few causes to which geologists attribute more importance.
The very fact that enormous deltas have been formed at the mouths of
many rivers—in other words, the actual growth of continents through
the effects of rainfall—is a proof how largely this cause must tend
to destroy and disintegrate the interiors of our continents. Dwelling
on this point, Sir Charles Lyell presents the following remarkable
illustration: ‘During a tour in Spain,’ he writes, ‘I was surprised to
see a district of gently undulating ground in Catalonia, consisting of
red and grey sandstone, and in some parts of red marl, almost entirely
denuded of herbage; while the roots of the pines, holm oaks, and some
other trees, were half exposed, as if the soil had been washed away
by a flood. Such is the state of the forests, for example, between
Oristo and Vich, and near San Lorenzo. But being overtaken by a violent
thunderstorm in the month of August, I saw the whole surface, even
the highest levels of some flat-topped hills, streaming with mud,
while on every declivity the devastation of torrents was terrific.
The peculiarities in the physiognomy of the district were at once
explained; and I was taught that, in speculating on the greater effects
which the direct action of rain may once have produced on the surface
of certain parts of England, we need not revert to periods when the
heat of the climate was tropical.’