EFFECTS OF EARTHQUAKES ON LAND,
1. Cracks and fissures—Materials discharged from
fissures—Explanation of fissure phenomena. 2. Disturbances in
lakes, rivers, springs, wells, fumaroles, &c.—Explanation of
these latter phenomena. 3. Permanent displacement of ground—On
coast lines—Level tracts—Among mountains—Explanation of these
movements.
_Cracks and fissures formed in the ground._—Almost all large
earthquakes have produced cracks in the ground. The cracks which were
found in the ground at Yokohama (February 22, 1880) were about two or
three inches wide, and from twenty to forty yards in length. They could
be best seen as lines along a road running near the upper edge of some
cliffs which overlook the sea at that place. The reason that cracks
should have occurred in such a position rather than in others was
probably owing to the greater motion at such a place, due to the face
of the cliff being unsupported, and there being no resistance opposed
to its forward motion. It often happens that earthquake cracks are many
feet in width. At the Calabrian earthquake of 1783, one or two of the
crevasses which were formed were more than 100 feet in width and 200
feet in depth. Their lengths varied from half a mile to a mile.[37]
Besides these large cracks, many smaller ones of one or two feet in
breadth and of great length were formed. In the large fissures many
houses were engulfed. Subsequent excavations showed that by the closing
of the fissures these had been jammed together to form one compact
mass. These cracks are usually more or less parallel, and at the same
time parallel to some topographical feature, like a range of mountains.
For example, the cracks which were formed by the Mississippi earthquake
of 1812 ran from north-east to south-west parallel to the Alleghanies.
By succeeding shocks these crevasses are sometimes closed and sometimes
opened still wider. Their permanency will also depend upon the nature
of the materials in which they are made.
During an earthquake large cracks may suddenly open and shut.
During the convulsions of 1692 which destroyed Port Royal, it is said
that many of the fissures which were formed, opened and shut. In some
of these, people were entirely swallowed up and buried. In others they
were trapped by the middle, and even by the neck, where if not killed
instantaneously they perished slowly. Subsequently their projecting
parts formed food for dogs.[38]
The earthquake which, July 18, 1880, shook the Philippines caused many
fissures to be found, which in some places were so numerous that the
ground was broken up into steps. Near to the village of San Antonio the
soil was so disturbed that the surface of a field of sugar-canes was
so altered that in some cases the top of one row of full grown plants
was on a level with the roots of the next. Into one such fissure a boat
disappeared, and into another, a child.
Subsequently the child was excavated, and its body, which was found a
short distance below the surface, was completely crushed.[39]
At the time of the Riobamba earthquake, not only were men engulfed,
but animals, like mules, also sank into the fissures which were formed.
The fissures which were formed at the time of the Owen’s Valley
earthquake in 1872 extended for miles nearly parallel to the
neighbouring Sierras. In some places the ground between the fissures
sank twenty or thirty feet, and at one place about three miles east of
Independence, a portion of the road was carried eighteen feet to the
south by a fissure.[40]
Speaking generally, it may be said that all large earthquakes are
accompanied by the formation of fissures. The Japanese have a saying
that at the time of a large earthquake persons must run to a bamboo
grove.
The object of this is to escape the danger of being engulfed in
fissures, the ground beneath a bamboo grove being so netted together
with fine roots that it is almost impossible for it to be rent open.
_Materials discharged from fissures._—Together with the opening of
cracks in the earth it often has happened that water, mud, vapours,
gases, and other materials, have been ejected.
At the time of the Mississippi earthquake water, mixed with sand and
mud, was thrown out with such violence that it spurted above the tops
of the highest trees. In Italy such phenomena have often been repeated.
From the fissures which were formed in 1692 at the time of the
earthquakes in Sicily, water issued which in some instances was
salt.[41]
By the Cachar earthquake (January 10, 1869) numerous fissures were
formed parallel to the banks of a river, from this water and mud were
ejected. Dr. Oldham, who describes this earthquake, says that the
first shot of dry mud or sand was mistaken for smoke or steam. The
water was foul, and hotter than surface water at the time, but only
slightly so; and the sulphurous smell was nothing more than you would
perceive in stirring up the mud at the bottom of any stagnant pool
which had lain undisturbed for some time.[42]
In 1755, when Tauris was destroyed, boiling water issued from the
cracks which were formed. Similar phenomena were witnessed at a place
eight miles from La Banca in Mexico, in the year 1820. Part of this hot
water was pure and part was muddy.
Sometimes the water which has been ejected has been so muddy that the
mud has been collected to form small hills. This was the case at the
time of the Riobamba earthquake. The mud in this case consisted partly
of coal, fragments of augite, and shells of infusoria.
At the time of the Jamaica earthquake men who had fallen into crevices
were in some cases thrown out again by issuing water.
Sometimes, as has already been mentioned, vapour, gases, and even
flames issue from fissures. Vapour of sulphur appears to be exceedingly
common. Kluge says that many fish were killed in consequence of the
sulphurous vapours which rose in the sea near to the coast of New
Zealand in 1855.
On December 14, 1797, an insupportable smell of sulphur was observed to
have accompanied the earthquake which at that time shook Cumana, which
was greatest when the disturbance was greatest.
Sulphurous fumes which were combustible were belched out of the
earth at the time of the Jamaica earthquake in 1692. The smell which
accompanied this was so powerful that it caused a general sickness
which swept away about 3,000 persons.[43]
From the fissures formed at Concepcion in 1835, water, which was black
and fœtid, issued.[44]
The earthquakes of New England in 1727 were accompanied by the
formation of fissures, from which sand and water boiled out in
sufficient quantity to form a quagmire. In some places ash and sulphur
are said to have been ejected.
At one house the stink of sulphur accompanying the earthquake was so
great that the family could not bear to remain in doors.[45]
Emanations of gas sometimes appear to have burst out from submarine
sources.
Thus the earthquake at Lima, in March, 1865, was accompanied with great
agitation of the water and an odour of sulphuretted and carburetted
hydrogen. This former gas was developed to such an extent that the
white paint of the U.S. ship ‘Lancaster’ was blackened.[46] With the
smell, flames have sometimes been observed, as, for instance, at the
time of the Lisbon earthquake.
At the time of the earthquakes of 1811 and 1813, in the Mississippi
valley, steam and smoke issued from some of the fissures which were
formed.
Instances are recorded where stones have been shot up from fissures
unaccompanied by water, as, for instance, at the earthquake of Pasto
(January, 1834). It is imagined that the propelling power must have
been the sudden expansion of escaping gases.
It has been suggested that flames seen above fissures might perhaps
be due to the burning of materials like sulphur. Mr. D. Forbes, who
examined the effects of the earthquakes of Mendoza, which were felt for
a distance of 1,200 miles, says that where the hard rock came to the
surface there were no traces of fissures, these being entirely confined
to the alluvium. The rumours of fire and smoke having appeared at some
of the fissures were without foundation, the presumed smoke being
nothing but dust.[47]
In addition to flames lights appear often to have been observed, the
origin of which cannot be easily explained.
The earthquake of November 22, 1751, at Genoa is said to have been
accompanied by a light like that of a prodigious fire which seemed to
arise out of the ground.[48]
_Explanation of fissure phenomena._—The manner in which fissures are
formed has already been explained when referring to the want of support
in the face of hills (page 136).
Similar remarks may be applied to the banks of rivers and all
depressions, whether natural or artificial, which have a steep slope.
At such places the wave of shock emerges on a free surface, which,
being unsupported in the direction of its motion, tends to tear itself
away from the material behind, and form a fissure parallel to the face
of the free surface. The distance of the fissure from the face of the
free surface will, theoretically, be equal to half the amplitude of the
wave of motion, one half tending to move forwards, and the other half
backwards. The reason that water and other materials rush forth from
fissures has been explained by Schüler as being due to cracks having
been opened through impervious strata, which, before the earthquake,
by their continuity prevented the rising of subterranean water under
hydrostatic pressure.[49]
Kluge explains the coming up of the waters as being due to the same
causes which he considers may be the origin of disturbances in the sea.
The most reasonable explanations of the eruption of water, mud, sand,
and gas through fissures are those given by Oldham and Mallet in their
account of the Cachar earthquake.
In the case of a horizontal shock passing through a bed of ooze or
water-bearing strata, the elastic wave will tend to pack up the water
during the forward motion to such an extent that it will flow or
spout up through any aperture communicating with the surface. By the
repetition of these movements causing ejections, sand or mud cones,
like those produced by a volcanic eruption, may be formed, and by a
similar action water may be shot violently up out of wells, as was the
case in Jamaica in 1692.
If an emergent wave acts through a water-bearing bed upon a
superincumbent layer of impervious material, this upper layer is,
during the upward motion, by its inertia suddenly pressed down upon the
latter.
This pressure is equal to that which would raise the upper layer to
a height equal to the amplitude of the motion of an earth particle,
and with a velocity at least equal to the mean velocity of the earth
particle resolved in the vertical direction.
For a moment the water-bearing strata receive an enormous squeeze, and
the water or mud starts up through any crevice which may be formed
leading to the surface.
From this we see that liquids may rise far beyond the level due to
hydrostatic pressure.[50]
Volger has attributed the origin of lights or flames appearing above
fissures to the friction which must take place between various rocky
materials at the time when the fissures are opened. As confirmatory of
this he refers to instances where similar phenomena have been observed
at the time of landslips. At the time of these landslips the heat
developed by friction has been sufficiently intense to convert water
into steam, the tension of which threw mud and earth into the air like
the explosion of a mine.[51]
The gas eruptions which occasionally take place with earthquakes are
probably due to the opening of fissures communicating with reservoirs
or strata charged with products of natural distillation, or chemical
action, which previously had accumulated beneath impervious strata. Of
the existence of such gases we have abundant evidence. In coal mines we
have fire damp which escapes in increased quantities with a lowering of
the barometrical pressure. In volcanic regions we have many examples of
natural springs of carbon dioxide.
These various gases sometimes escape in quantity, or erupt without
the occurrence of earthquakes. Rossi mentions an instance where a few
years ago quantities of fish were killed by the eruption of gas in the
Tiber, near Rome. Another instance is one which occurred at Follonica
on April 6, 1874. On the morning of that day many of the streets and
roads were covered with the dead bodies of rats and mice. It seemed as
if it had rained rats. From the facts that the bodies of the creatures
seemed healthy, that the destruction had happened suddenly, and not
come on gradually like an epidemic, it was supposed that they had been
destroyed by an emanation of carbon dioxide. The fact that many of them
lay in long lines suggested the idea that they had been endeavouring
to escape at the time of the eruption.[52] If we can suppose sudden
developments of gas like this to have occasionally accompanied
earthquakes, we may sometimes have the means of accounting for the
sickness which has been felt.
_Disturbances in lakes._—It has often been observed that, at the time
of large earthquakes, lakes have been thrown into violent agitation,
and their waters have been raised or lowered. At the time of the great
Lisbon earthquake, not only were the waters of European lakes thrown
into a state of oscillation, but similar effects were produced in the
great lakes of North America. In some instances, as in the case of
small ponds, these movements may be produced by the horizontal backward
and forward motion of the ground. At other times they are probably due
to an actual tipping of a portion of their basins. Movements like these
latter will be again referred to in the chapter on Earth Pulsations.
On January 27, 1856, there was a shock of earthquake at Bailyborough,
Ireland, which occasioned an adjacent lough to overflow its banks
and rush into the town with great impetuosity. In returning it swept
away two men, leaving behind a great quantity of pike and eels of a
prodigious growth.[53]
_Disturbances in rivers._—Just as lakes have been disturbed, so also
have there been sudden disturbances in rivers. Sometimes these have
overflowed their banks, whilst at other times they have been suddenly
dried up. In certain cases the reason that a portion of a river should
have become dry has been very apparent, as, for instance, at the time
of the Zenkoji earthquake in Japan in 1847, when the Shikuma-gawa
became partly dry in consequence of the large masses of earth which
had been shaken down from overhanging cliffs damming a portion of
its course, and thus forming, first, lakes, and subsequently, new
water-courses. As another example, out of the many which might be
quoted, may be mentioned the sudden drying up of the river Aboat,
a tributary of the Magat, in the Philippine Islands, on July 27,
1881, shortly after a severe shock of earthquake. The water of this
river ceased to flow for two hours, after which it reappeared with
considerable increase of volume and of a reddish colour. Signor E. A.
Casariego, who describes this, remarks that the phenomenon could easily
be explained through the slipping down of the steep banks in narrow
parts of its upper valley, by which means its flow had been obstructed
until the water had time to accumulate and pass over or demolish the
obstruction.
After the earthquake of Belluno (June 29, 1873), the torrent Tesa,
which is ordinarily limpid, became very muddy.[54] Similar phenomena
have been observed even in Britain, as, for instance, in 1787, when, at
the time of a shock which was felt in Glasgow, there was a temporary
stoppage in the waters of the Clyde. Again, in 1110, there was a
dreadful earthquake at Shrewsbury and Nottingham, and the Trent became
so low at Nottingham that people walked over it.
The earthquake of 1158, which was felt in many parts of England, was
accompanied by the drying up of the Thames, which was so low that it
could be crossed on foot even at London.[55]
Facts analogous to these are mentioned in the accounts of many large
earthquakes. Sometimes rivers only come muddy or change their colour.
In an account of the Lisbon earthquake we read that some of the rivers
near Neufchâtel suddenly became muddy.[56]
At other times large waves are formed. Thus the earthquake of Kansas
(April 24, 1867) apparently created a disturbance in the rivers at
Manhattan, which rolled in a heavy wave from the north to the south
bank.[57]
Sometimes curious phenomena have happened with regard to rivers without
the occurrence of earthquakes. Thus, for instance, on November 27,
1838, there was a simultaneous stoppage of the Teviot, Clyde, and Nith.
In these rivers similar phenomena have been observed in previous years.
Again, on January 1, 1755, there was a sudden sinking of the river
Frooyd, near Pontypool. This appears to have been due to the water
sinking into chasms which were suddenly opened.[58]
_Effects produced in springs, wells, fumaroles, &c._—Springs also are
often affected by earthquakes. Sometimes the character of their waters
change; those which were pure become muddy, whilst those which were hot
have their temperature altered.
Sometimes springs have been dried up, whilst at other times new springs
have been formed.
This latter was the case in New England (October 27, 1727). In some
places springs were formed, whilst at other places they were either
entirely or partly dried up.[59]
At and near Lisbon, in 1755, some fountains became muddy, others
decreased, others increased, and others dried up. At Montreux, Aigle,
and other places, springs became turbid.
The baths at Toplitz, in Bohemia, which were discovered in
A.D. 762, were seriously affected by the same earthquake.
Previous to the earthquake it is said that they had always given a
constant supply of hot water. At this time, however, the chief spring
sent up vast quantities of water and ran over. One hour before this
it had grown turbid and flowed muddy. After this it stopped for about
one minute, but recommenced to flow with prodigious violence, driving
before it considerable quantities of reddish ochre. Finally, it settled
back to its original clear state and flowed as before.[60]
In 1855, at the earthquake of Wallis, many new springs burst forth, and
some of these in Nicolai Thale were so rich in iron that they quickly
formed a deposit of ochre.
At the time of the Belluno earthquake (June 29, 1873), a hot spring, La
Vena d’Oro, suddenly became red.[61]
The following examples of like changes are taken from the writings of
Fuchs.[62]
In 1738 the hot springs of St. Euphema rose considerably in their
temperature.
During the earthquake of October, 1848, the hot springs of Ardebil,
which usually had a temperature of from 44° to 46° C., rose so high
that their temperature was sufficient to cause scalding.
At the time of the earthquake of Wallis, in 1855, the temperature of
hot springs rose 7°, and the quantity of water increased three times.
During the earthquake of 1835 in Chili, the springs of Cauquenes fell
from 118° to 92° F. Subsequently, however, they again rose.
Fumaroles are similarly disturbed. Thus, at the time of the earthquakes
of Martinique (September, 1875), the fumaroles there showed an abnormal
activity.[63]
Wells often appear to be acted upon in the same manner as springs.
At the time of the California earthquake (April, 1855), the level of
the water in certain wells was raised ten to twelve feet.
A consequence of the earthquake at Neufchâtel, in 1749, was to fill
some of the wells with mud.[64] At Constantinople, on September 2,
1754, wells became dry.[65]
_Explanation of the above phenomena._—That the water in springs and
wells should be caused to rise at the time of an earthquake, admits of
explanation on the supposition of compressions taking place similar
to those which cause the rise of water in fissures. That the water in
wells and springs should be rendered turbid, is partly explained on the
supposition of more or less dislocation taking place in the earthy or
rocky cavities in which they are contained or through which they flow.
At the time of a large earthquake it is extremely probable that there
is a general disturbance in the lines of circulation of subterranean
waters and gases throughout the shaken area. By these disturbances, new
waters may be brought to the surface, two or more lines of circulation
may be united, and the flow of a spring or supply of a well be
augmented. Fissures, through which waters reached the surface, may be
closed, wells may become dry, or springs may cease to flow, hot springs
may have their temperature lowered by the additions of cold water
from another source, and, in a similar manner, waters may be altered
in their mineralisation. An important point to be remembered in this
consideration is the mutual dependence of various underground water
supplies, and the area over which any given supply may circulate. A
well in the higher part of Lincoln Heath is said to be governed by the
river Trent, which is ten miles distant; when the river rises the well
rises in proportion, and when the river falls the water in the well
falls.[66]
The change which is usually observed in hot springs is, that before or
with earthquakes they increase in temperature, but afterwards sink back
to their normal state. This increase in temperature may possibly be due
to communication being opened with new or deeper centres of volcanic
activity, or a temporarily increased rate of flow.
That the water issuing from newly formed fissures or springs should
be hot, might be explained on the supposition of its arising from a
considerable depth, or from some volcanic centre. It might also be
attributed to the heat developed by friction at the opening of the
fissures. These changes which earthquakes produce upon the underground
circulation of waters are phenomena deserving especial attention.
Although we know much about the circulation of surface water, it is but
little that we yet know about the movement of the streams hidden from
view, from which these surface waters have their sources. Earthquakes
may be regarded as gigantic experiments on the circulatory system of
the earth, which, if properly interpreted, may yield information of
scientific and utilitarian value.
The sudden elevations, depressions, or lateral shifting of large tracts
of country at the time of destructive earthquakes are phenomena
with which all students of geology are familiar. In most cases these
displacements have been permanent; and evidences of many of the
movements which occurred within the memory of man, remain as witnesses
of the terrible convulsions with which they were accompanied.
_Movements on coast lines and level tracts._—At the time of the
great earthquake of Concepcion, on February 20, 1835, much of the
neighbouring coast line was suddenly elevated four or five feet
above sea level. This, however, subsequently sank until it was only
two feet. A rocky flat, off the island of Santa Maria, was lifted
above high-water mark, and left covered with ‘gaping and putrefying
mussel-shells, still attached to the bed on which they had lived.’ The
northern end of the island itself was raised ten feet and the southern
extremity eight feet.[67]
By the earthquake of 1839, the island of Lemus, in the Chonos
Archipelago, was suddenly elevated eight feet.[68]
Of movements like these, especially along the western shores of South
America, Darwin, who paid so much attention to this subject, has given
many examples. In 1822, the shore near Valparaiso was suddenly lifted
up, and Darwin tells us that he heard it confidently asserted ‘that a
sentinel on duty, immediately after the shock, saw a part of a fort
which previously was not within the line of his vision, and this would
indicate that the uplifting was not vertical.’[69] That the large areas
of land should be shifted permanently in horizontal directions, as well
as vertically, we should anticipate from the observations which we are
able to make upon large fissures which are caused by earthquakes.
Another remarkable example of sudden movement in the rocky crust is
that which took place during the earthquakes of 1811–12 in the valley
of the Mississippi, near to the mouth of the Ohio, which was convulsed
to such a degree, that lakes, twenty miles in extent, were formed
in the course of an hour. This country, which is called the ‘sunk
country,’ extends some seventy to eighty miles north and south, and
thirty miles east and west.[70]
In the ‘Gentleman’s Magazine’ we read of the little territory of
Causa Nova, in Calabria, being sunk twenty-nine feet into the earth
by an earthquake, without throwing down a house. The inhabitants,
being warned by a noise, escaped into the fields, and only five were
killed.[71]
Other examples of these permanent dislocations of strata are to be
found in almost every text-book on geology.
_Geological changes produced._—Passing over the accounts of earth
movements which are more or less fictitious, and confining our
attention to the well authenticated facts, we see at once the important
part which earthquakes have played as agents working geological
changes. Even in the nineteenth century long tracts of coast, as in
Chili and New Zealand, have been raised, whilst other areas, like the
Delta of the Indus, have been sunk. Sir H. Bartle Frere, speaking about
the disturbance which took place in his latter region in 1819, remarks
that all the canals drawn from the Fullalee River ceased to run for
about three days, probably indicating a general upheaval of the lower
part of the canal. In consequence of the earthquakes in former times
it is not unlikely that water-courses have ceased to flow, water has
decreased in wells, and districts have been depopulated.[72]
Sometimes these changes have taken place gradually and sometimes with
violence. Mountains have been toppled over, valleys have been filled,
cities have been submerged or buried.
With the records of these convulsions before us, we see that seismic
energy yet exhibits a terrible activity in changing the features of the
globe.
_Reason of these movements._—To formulate a single reason for these
catastrophes would be difficult. Where they are of the nature of
landslips, or materials have been dislodged from mountain sides, the
cause is evidently the sudden movement of this ground acting upon
strata not held together in a sufficiently stable condition. A similar
explanation may be given for the sudden elevations or depressions of
strata in a district removed from the centre where the disturbance had
its origin. The seismic effort exhibits itself in a certain area round
its origin as a sudden push, and by this push, strata are fractured and
caused to move relatively to each other.
At or near to the origin of an earthquake it might be argued that it
was the sudden falling of rocky strata towards a position of stable
equilibrium that caused the shaking, and in such a case the movements
referred to may be regarded as the cause rather than the effect of an
earthquake.
A subject closely connected with the sudden dislocation of strata,
is the production of secondary or consequent earthquakes, due to the
disturbance of ground in a critical state (see p. 248).