EARTHQUAKE IN CALABRIA, 1783.
Earthquake in Calabria, February 5, 1783--Shocks continued to the
end of the year 1786--Authorities--Area convulsed--Geological
structure of the district--Difficulty of ascertaining changes of
level--Subsidence of the quay at Messina--Movement in the stones of
two obelisks--Shift or fault in the Round Tower of
Terranuova--Opening and closing of fissures--Large edifices
engulfed--Dimensions of new caverns and fissures--Gradual closing in
of rents--Bounding of detached masses into the
air--Landslips--Buildings transported entire to great distances--New
lakes--Funnel-shaped hollows in alluvial plains--Currents of
mud--Fall of cliffs, and shore near Scilla inundated--State of
Stromboli and Etna during the shocks--How earthquakes contribute to
the formation of valleys--Concluding remarks.
_Calabria_, 1783.--Of the numerous earthquakes which have occurred in
different parts of the globe, during the last 100 years, that of
Calabria, in 1783, is almost the only one of which the geologist can be
said to have such a circumstantial account as to enable him fully to
appreciate the changes which this cause is capable of producing in the
lapse of ages. The shocks began in February, 1783, and lasted for nearly
four years, to the end of 1786. Neither in duration, nor in violence,
nor in the extent of territory moved, was this convulsion remarkable,
when contrasted with many experienced in other countries, both during
the last and present century; nor were the alterations which it
occasioned in the relative level of hill and valley, land and sea, so
great as those effected by some subterranean movements in South America,
in later times. The importance of the earthquake in question arises from
the circumstance, that Calabria is the only spot hitherto visited, both
during and after the convulsions, by men possessing sufficient leisure,
zeal, and scientific information, to enable them to collect and describe
with accuracy the physical facts which throw light on geological
questions.
[Illustration: Fig. 42.]
_Authorities._--Among the numerous authorities, Vivenzio, physician to
the king of Naples, transmitted to the court a regular statement of his
observations during the continuance of the shocks; and his narrative is
drawn up with care and clearness.[663] Francesco Antonio Grimaldi, then
secretary of war, visited the different provinces at the king's command,
and published a most detailed description of the permanent changes in
the surface.[664] He measured the length, breadth, and depth of the
different fissures and gulfs which opened, and ascertained their number
in many provinces. His comments, moreover, on the reports of the
inhabitants, and his explanations of their relations, are judicious and
instructive. Pignataro, a physician residing at Monteleone, a town
placed in the very centre of the convulsions, kept a register of the
shocks, distinguishing them into four classes, according to their degree
of violence. From his work, it appears that, in the year 1783, the
number was 949, of which 501 were shocks of the first degree of force;
and in the following year there were 151, of which 98 were of the first
magnitude.
Count Ippolito, also, and many others, wrote descriptions of the
earthquake; and the Royal Academy of Naples, not satisfied with these
and other observations, sent a deputation from their own body into
Calabria, before the shocks had ceased, who were accompanied by artists
instructed to illustrate by drawings the physical changes of the
district, and the state of ruined towns and edifices. Unfortunately
these artists were not very successful in their representations of the
condition of the country, particularly when they attempted to express,
on a large scale, the extraordinary revolutions which many of the great
and minor river-courses underwent. But many of the plates published by
the Academy are valuable; and as they are little known, I shall
frequently avail myself of them to illustrate the facts about to be
described.[665]
In addition to these Neapolitan sources of information, our countryman,
Sir William Hamilton, surveyed the district, not without some personal
risk, before the shocks had ceased; and his sketch, published in the
Philosophical Transactions, supplies many facts that would otherwise
have been lost. He has explained, in a rational manner, many events
which, as related in the language of some eye-witnesses, appeared
marvellous and incredible. Dolomieu also examined Calabria during the
catastrophe, and wrote an account of the earthquake, correcting a
mistake into which Hamilton had fallen, who supposed that a part of the
tract shaken had consisted of volcanic tuff. It is, indeed, a
circumstance which enhances the geological interest of the commotions
which so often modify the surface of Calabria, that they are confined to
a country where there are neither ancient nor modern rocks of volcanic
or trappean origin; so that at some future time, when the era of
disturbance shall have passed by, the cause of former revolutions will
be as latent as in parts of Great Britain now occupied exclusively by
ancient marine formations.
_Extent of the area convulsed._--The convulsion of the earth, sea, and
air extended over the whole of Calabria Ultra, the southeast part of
Calabria Citra, and across the sea to Messina and its environs; a
district lying between the 38th and 39th degrees of latitude. The
concussion was perceptible over a great part of Sicily, and as far north
as Naples; but the surface over which the shocks acted so forcibly as to
excite intense alarm did not generally exceed 500 square miles in area.
The soil of that part of Calabria is composed chiefly, like the southern
part of Sicily, of calcareo-argillaceous strata of great thickness,
containing marine shells. This clay is sometimes associated with beds of
sand and limestone. For the most part these formations resemble in
appearance and consistency the Subapennine marls, with their
accompanying sands and sandstones; and the whole group bears
considerable resemblance, in the yielding nature of its materials, to
most of our tertiary deposits in France and England. Chronologically
considered, however, the Calabrian formations are comparatively of
modern date, often abounding in fossil shells referable to species now
living in the Mediterranean.
We learn from Vivencio, that on the 20th and 26th of March, 1783,
earthquakes occurred in the islands of Zante, Cephalonia, and St. Maura;
and in the last-mentioned island several public edifices and private
houses were overthrown, and many people destroyed.
If the city of Oppido, in Calabria Ultra, be taken as a centre, and
round that centre a circle be described, with a radius of twenty-two
miles, this space will comprehend the surface of the country which
suffered the greatest alteration, and where all the towns and villages
were destroyed. The first shock, of February 5th, 1783, threw down, in
two minutes, the greater part of the houses in all the cities, towns,
and villages, from the western flanks of the Apennines in Calabria Ultra
to Messina in Sicily, and convulsed the whole surface of the country.
Another occurred on the 28th of March, with almost equal violence. The
granitic chain which passes through Calabria from north to south, and
attains the height of many thousand feet, was shaken but slightly by the
first shock, but more rudely by some which followed.
Some writers have asserted that the wave-like movements which were
propagated through the recent strata, from west to east, became very
violent when they reached the point of junction with the granite, as if
a reaction was produced where the undulatory movement of the soft strata
was suddenly arrested by the more solid rocks. But the statement of
Dolomieu on this subject is most interesting, and perhaps, in a
geological point of view, the most important of all the observations
which are recorded.[666] The Apennines, he says, which consist in great
part of hard and solid granite, with some micaceous and argillaceous
schists, form bare mountains with steep sides, and exhibit marks of
great degradation. At their base newer strata are seen of sand and clay,
mingled with shells; a marine deposit containing such ingredients as
would result from the decomposition of granite. The surface of this
newer (_tertiary_) formation constitutes what is called the plain of
Calabria--a platform which is flat and level, except where intersected
by narrow valleys or ravines, which rivers and torrents have excavated
sometimes to the depth of six hundred feet. The sides of these ravines
are almost perpendicular; for the superior stratum, being bound together
by the roots of trees, prevents the formation of a sloping bank. The
usual effect of the earthquake, he continues, was to disconnect all
those masses which either had not sufficient bases for their bulk, or
which was supported only by lateral adherence. Hence it follows that
throughout almost the whole length of the chain, the soil which adhered
to the granite at the base of the mountains Caulone, Esope, Sagra, and
Aspramonte, slid over the solid and steeply inclined nucleus, and
descended somewhat lower, leaving almost uninterruptedly from St. George
to beyond St. Christina, a distance of from nine to ten miles, a chasm
between the solid granitic nucleus and the sandy soil. Many lands
slipping thus were carried to a considerable distance from their former
position, so as entirely to cover others; and disputes arose as to whom
the property which had thus shifted its place should belong.
From this account of Dolomieu we might anticipate, as the result of a
continuance of such earthquakes, first, a longitudinal valley following
the line of junction of the older and newer rocks; secondly, greater
disturbance in the newer strata near the point of contact than at a
greater distance from the mountains; phenomena very common in other
parts of Italy at the junction of the Apennine and Subapennine
formations.
Mr. Mallet, in his valuable essay on the Dynamics of Earthquakes,[667]
offers the following explanation of the fact to which Dolomieu has
called attention. When a wave of elastic compression, of which he
considers the earth-wave to consist, passes abruptly from a body having
an extremely low elasticity, such as clay and gravel, into another like
granite, whose elasticity is remarkably high, it changes not only its
velocity but in part also its course, a portion being reflected and a
portion refracted. The wave being thus sent back again produces a shock
in the opposite direction, doing great damage to buildings on the
surface by thus returning upon itself. At the same time, the shocks are
at once eased when they get into the more elastic materials of the
granitic mountains.
The surface of the country during the Calabrian earthquakes often heaved
like the billows of a swelling sea, which produced a swimming in the
head, like sea-sickness. It is particularly stated, in almost all the
accounts, that just before each shock the clouds appeared motionless;
and, although no explanation is offered of this phenomenon, it is
obviously the same as that observed in a ship at sea when it pitches
violently. The clouds seem arrested in their career as often as the
vessel rises in a direction contrary to their course; so that the
Calabrians must have experienced precisely the same motion on the land.
Trees, supported by their trunks, sometimes bent during the shocks to
the earth, and touched it with their tops. This is mentioned as a
well-known fact by Dolomieu; and he assures us that he was always on his
guard against the spirit of exaggeration in which the vulgar are ever
ready to indulge when relating these wonderful occurrences.
It is impossible to suppose that these waves, which are described in
Italy and other regions of earthquakes as passing along the solid
surface of the earth in a given direction like a billow on the sea, have
any strict analogy with the undulations of a fluid. They are doubtless
the effects of vibrations, radiating from some deep-seated point, each
of which on reaching the surface lifts up the ground, and then allows it
again to subside. As the distance between the source of the subterranean
movement and the surface must vary according to the outline of the
country, so the vibratory jar will reach different points in succession.
[Illustration: Fig. 75.
Shifts in the stones of two obelisks in the Convent of St Bruno.]
The Academicians relate that in some of the cities of Calabria effects
were produced seeming to indicate a whirling or vorticose movement.
Thus, for example, two obelisks (fig. 75) placed at the extremities of a
magnificent facade in the convent of S. Bruno, in a small town called
Stefano del Bosco, were observed to have undergone a movement of a
singular kind. The shock which agitated the building is described as
having been horizontal and vorticose. The pedestal of each obelisk
remained in its original place; but the separate stones above were
turned partially round, and removed sometimes nine inches from their
position without falling.
It has been suggested by Mr. Darwin that this kind of displacement may
be due to a vibratory rather than a whirling motion;[668] and more
lately Mr. Mallet, in the paper already cited, has offered a very
ingenious solution of the problem. He refers the twisting simply to an
elastic wave, which has moved the pedestal forwards and back again, by
an alternate horizontal motion within narrow limits, and he has
succeeded in showing that a rectilinear movement in the ground may have
sufficed to cause an incumbent body to turn partially round upon its
bed, provided a certain relation exist between the position of the
centre of gravity of the body and its centre of adherence.[669]
I shall now consider, in the first place, that class of physical changes
produced by the earthquake which are connected with alterations in the
relative level of the different parts of the land; and afterwards
describe those which are more immediately connected with the derangement
of the regular drainage of the country, and where the force of running
water co-operated with that of the earthquake.
_Difficulty of ascertaining changes of level._--In regard to alterations
of relative level, none of the accounts establish that they were on a
considerable scale; but it must always be remembered that, in proportion
to the area moved is the difficulty of proving that the general level
has undergone any change, unless the sea-coast happens to have
participated in the principal movement. Even then it is often impossible
to determine whether an elevation or depression even of several feet has
occurred, because there is nothing to attract notice in a band of
shingle and sand of unequal breadth above the level of the sea running
parallel to a coast; such bands generally marking the point reached by
the waves during spring tides, or the most violent tempests. The
scientific investigator has not sufficient topographical knowledge to
discover whether the extent of beach has diminished or increased; and he
who has the necessary local information, scarcely ever feels any
interest in ascertaining the amount of the rise or fall of the ground.
Add to this the great difficulty of making correct observations, in
consequence of the enormous waves which roll in upon a coast during an
earthquake, and efface every landmark near the shore.
_Subsidence of the quay at Messina._--It is evidently in seaports alone
that we can look for very accurate indications of slight changes of
level; and when we find them, we may presume that they would not be rare
at other points, if equal facilities of comparing relative altitudes
were afforded. Grimaldi states (and his account is confirmed by Hamilton
and others), that at Messina, in Sicily, the shore was rent; and the
soil along the port, which before the shock was perfectly level, was
found afterwards to be inclined towards the sea,--the sea itself near
the "Banchina" becoming deeper, and its bottom in several places
disordered. The quay also sunk down about fourteen inches below the
level of the sea, and the houses in its vicinity were much fissured.
(_Phil. Trans._ 1783.)
Among various proofs of partial elevation and depression in the
interior, the Academicians mention, in their Survey, that the ground was
sometimes on the same level on both sides of new ravines and fissures,
but sometimes there had been a considerable shifting, either by the
upheaving of one side, or the subsidence of the other. Thus, on the
sides of long rents in the territory of Soriano, the stratified masses
had altered their relative position to the extent of from eight to
fourteen palms (six to ten and a half feet).
_Polistena._--Similar shifts in the strata are alluded to in the
territory of Polistena, where there appeared innumerable fissures in the
earth. One of these was of great length and depth; and in parts the
level of the corresponding sides was greatly changed. (See fig. 76.)
_Terranuova._--In the town of Terranuova some houses were seen uplifted
above the common level, and others adjoining sunk down into the earth.
In several streets the soil appeared thrust up, and abutted against the
walls of houses: a large circular tower of solid masonry, part of which
had withstood the general destruction, was divided by a vertical rent,
and one side was upraised, and the foundations heaved out of the ground.
It was compared by the Academicians to a great tooth half extracted
from the alveolus, with the upper part of the fangs exposed. (See fig.
77.)
[Illustration: Fig. 76.
Deep fissure, near Polistena, caused by the earthquake of 1783.]
Along the line of this shift, or "fault," as it would be termed
technically by miners, the walls were found to adhere firmly to each
other, and to fit so well, that the only signs of their having been
disunited was the want of correspondence in the courses of stone on
either side of the rent.
[Illustration: Fig. 77.
Shift or "fault" in the Round Tower of Terranuova in Calabria,
occasioned by the earthquake of 1783.]
Dolomieu saw a stone well in the convent of the Augustins at Terranuova,
which had the appearance of having been driven out of the earth. It
resembled a small tower eight or nine feet in height, and a little
inclined. This effect, he says, was produced by the consolidation and
consequent sinking of the sandy soil in which the well was dug.
In some walls which had been thrown down, or violently shaken, in
Monteleone, the separate stones were parted from the mortar, so as to
leave an exact mould where they had rested; whereas in other cases the
mortar was ground to dust between the stones.
It appears that the wave-like motions often produced effects of the most
capricious kind. Thus, in some streets of Monteleone, every house was
thrown down but one; in others, all but two; and the buildings which
were spared were often scarcely in the least degree injured. In many
cities of Calabria, all the most solid buildings were thrown down, while
those which were slightly built escaped; but at Rosarno, as also at
Messina in Sicily, it was precisely the reverse, the massive edifices
being the only ones that stood.
_Fissures._--It appears evident that a great part of the rending and
fissuring of the ground was the effect of a violent motion from below
upwards; and in a multitude of cases where the rents and chasms opened
and closed alternately, we must suppose that the earth was by turns
heaved up, and then let fall again.[670] We may conceive the same effect
to be produced on a small scale, if, by some mechanical force, a
pavement composed of large flags of stone should be raised up, and then
allowed to fall suddenly, so as to resume its original position. If any
small pebbles happened to be lying on the line of contact of two flags,
they would fall into the opening when the pavement rose, and be
swallowed up, so that no trace of them would appear after the subsidence
of the stones. In the same manner, when the earth was upheaved, large
houses, trees, cattle, and men were engulfed in an instant in chasms and
fissures; and when the ground sank down again, the earth closed upon
them, so that no vestige of them was discoverable on the surface. In
many instances, individuals were swallowed up by one shock, and then
thrown out again alive, together with large jets of water, by the shock
which immediately succeeded.
[Illustration: Fig. 78.
Fissures near Jerocarne, in Calabria, caused by the earthquake of 1783.]
At Jerocarne, a country which, according to the Academicians, was
_lacerated_ in a most extraordinary manner, the fissures ran in every
direction, "like cracks on a broken pane of glass" (see fig. 78); and as
a great portion of them remained open after the shocks, it is very
possible that this country was permanently upraised. It was usual, as we
learn from Dolomieu, for the chasms and fissures throughout Calabria, to
ran parallel to the course of some pre-existing gorges in their
neighborhood.
_Houses engulfed._--In the vicinity of Oppido, the central point from
which the earthquake diffused its violent movements, many houses were
swallowed up by the yawning earth, which closed immediately over them.
In the adjacent district, also, of Cannamaria four farm-houses, several
oil-stores, and some spacious dwelling-houses were so completely
engulfed in one chasm, that not a vestige of them was afterwards
discernible. The same phenomena occurred at Terranuova, S. Christina,
and Sinopoli. The Academicians state particularly, that when deep
abysses had opened in the argillaceous strata of Terranuova, and houses
had sunk into them, the sides of the chasms closed with such violence,
that, on excavating afterwards to recover articles of value, the workmen
found the contents and detached parts of the buildings jammed together
so as to become one compact mass. It is unnecessary to accumulate
examples of similar occurrences; but so many are well authenticated
during this earthquake in Calabria, that we may, without hesitation,
yield assent to the accounts of catastrophes of the same kind repeated
again and again in history, where whole towns are declared to have been
engulfed, and nothing but a pool of water or tract of sand left in their
place.
_Chasm formed near Oppido._--On the sloping side of a hill near Oppido a
great chasm opened; and, although a large quantity of soil was
precipitated into the abyss, together with a considerable number of
olive-trees and part of a vineyard, a great gulf remained after the
shock, in the form of an amphitheatre, 500 feet long and 200 feet deep.
(See fig. 79.)
[Illustration: Fig. 79.
Chasm formed by the earthquake of 1783, near Oppido in Calabria.]
_Dimensions of new fissures and chasms._--According to Grimaldi, many
fissures and chasms, formed by the first shock of February 5th, were
greatly widened, lengthened, and deepened by the violent convulsions of
March 28th. In the territory of San Fili this observer found a new
ravine, half a mile in length, two feet and a half broad, and
twenty-five feet deep; and another of similar dimensions in the
territory of Rosarno. A ravine _nearly a mile long_, 105 feet broad and
thirty feet deep, opened in the district of Plaisano, where, also, two
gulfs were caused--one in a place called Cerzulle, three-quarters of a
mile long, 150 feet broad, and above _one hundred feet deep_; and
another at La Fortuna, nearly a quarter of a mile long, above thirty
feet in breadth, and no less than 225 feet deep.
[Illustration: Fig. 80.
Chasm in the hill of St. Angelo, near Soriano, in Calabria, caused by
the earthquake of 1783.]
In the district of Fosolano three gulfs opened: one of these measured
300 feet square, and above thirty feet deep; another was nearly half a
mile long, fifteen feet broad, and above thirty-feet deep; the third was
750 feet square. Lastly, a calcareous mountain, called Zefirio, at the
southern extremity of the Italian peninsula, was cleft in two for the
length of nearly half a mile, and an irregular breadth of many feet.
Some of these chasms were in the form of a crescent. The annexed cut
(fig. 80) represents one by no means remarkable for its dimensions,
which remained open by the side of a small pass over the hill of St.
Angelo, near Soriano. The small river Mesima is seen in the foreground.
_Formation of circular hollows and new lakes._--In the report of the
Academy, we find that some plains were covered with circular hollows,
for the most part about the size of carriage-wheels, but often somewhat
larger or smaller. When filled with water to within a foot or two of the
surface, they appeared like wells; but, in general, they were filled
with dry sand, sometimes with a concave surface, and at other times
convex. (See fig. 81.) On digging down, they found them to be
funnel-shaped, and the moist loose sand in the centre marked the tube up
which the water spouted. The annexed cut (fig. 82) represents a section
of one of these inverted cones when the water had disappeared, and
nothing but dry micaceous sand remained.
[Illustration: Fig. 81.
Circular hollows in the plain of Rosarno, formed by the earthquake of
1783.]
[Illustration: Fig. 82.
Section of one of the circular hollows formed in the plain of Rosarno.]
A small circular pond of similar character was formed not far from
Polistena (see fig. 83); and in the vicinity of Seminara, a lake was
suddenly caused by the opening of a great chasm, from the bottom of
which water issued. This lake was called Lago del Tolfilo. It extended
1785 feet in length, by 937 in breadth, and 52 in depth. The
inhabitants, dreading the miasma of this stagnant pool, endeavored, at
great cost, to drain it by canals, but without success, as it was fed by
springs issuing from the bottom of the deep chasm.
Vivenzio states, that near Sitizzano a valley was nearly filled up to a
level with the high grounds on each side, by the enormous masses
detached from the boundary hills, and cast down into the course of two
streams. By this barrier a lake was formed of great depth, about two
miles long and a mile broad. The same author mentions that, upon the
whole, there were fifty lakes occasioned during the convulsions: and he
assigns localities to all of these. The government surveyors enumerated
215 lakes; but they included in this number many small ponds.
[Illustration: Fig. 83.
Circular pond near Polistena, in Calabria, caused by the earthquake in
1783.]
_Cones of sand thrown up._--Many of the appearances exhibited in the
alluvial plains, such as springs spouting up their water like fountains
at the moment of the shock, have been supposed to indicate the alternate
rising and sinking of the ground. The first effect of the more violent
shocks was usually to dry up the rivers, but they immediately afterwards
overflowed their banks. In marshy places, an immense number of cones of
sand were thrown up. These appearances Hamilton explains, by supposing
that the first movement raised the fissured plain from below upwards, so
that the rivers and stagnant waters in bogs sank down, or at least were
not upraised with the soil. But when the ground returned with violence
to its former position, the water was thrown up in jets through
fissures.[671]
The phenomenon, according to Mr. Mallet, may be simply an accident
contingent on the principal cause of disturbance, the rapid transit of
the earth-wave. "The sources," he says, "of copious springs usually lie
in flat plates or fissures filled with water, whether issuing from solid
rock, or from loose materials; now, if a vein, or thin flat cavity
filled with water, be in such a position that the plane of the plate of
water or fissure be transverse to the line of transit of the earth-wave,
the effect of the arrival of the earth-wave at the watery fissure will
be, at the instant, to compress its walls more or less together, and so
squeeze out the water, which will, for a moment, gush up at the
spring-head like a fountain, and again remain in repose after the
transit of the wave."
_Gradual closing in of fissures._--Sir W. Hamilton was shown several
deep fissures in the vicinity of Mileto, which, although not one of
them was above a foot in breadth, had opened so wide during the
earthquake as to swallow an ox and nearly one hundred goats. The
Academicians also found, on their return through districts which they
had passed at the commencement of their tour, that many rents had, in
that short interval, gradually closed in, so that their width had
diminished several feet, and the opposite walls had sometimes nearly
met. It is natural that this should happen in argillaceous strata,
while, in more solid rocks, we may expect that fissures will remain open
for ages. Should this be ascertained to be a general fact in countries
convulsed by earthquakes, it may afford a satisfactory explanation of a
common phenomenon in mineral veins. Such veins often retain their full
size so long as the rocks consist of limestone, granite, or other
indurated materials; but they contract their dimensions, become mere
threads, or are even entirely cut off, where masses of an argillaceous
nature are interposed. If we suppose the filling up of fissures with
metallic and other ingredients to be a process requiring ages for its
completion, it is obvious that the opposite walls of rents, where strata
consist of yielding materials, must collapse or approach very near to
each other before sufficient time is allowed for the accretion of a
large quantity of veinstone.
_Thermal waters augmented._--It is stated by Grimaldi, that the thermal
waters of St. Eufemia, in Terra di Amato, which first burst out during
the earthquake of 1638, acquired, in February, 1783, an augmentation
both in quantity and degree of heat. This fact appears to indicate a
connection between the heat of the interior and the fissures caused by
the Calabrian earthquakes, notwithstanding the absence of volcanic
rocks, either ancient or modern, in that district.
_Bounding of detached masses into the air._--The violence of the
movement of the ground upwards was singularly illustrated by what the
Academicians call the "sbalzo," or bounding into the air, to the height
of several yards, of masses slightly adhering to the surface. In some
towns a great part of the pavement stones were thrown up, and found
lying with their lower sides uppermost. In these cases, we must suppose
that they were propelled upwards by the momentum which they had
acquired; and that the adhesion of one end of the mass being greater
than that of the other, a rotatory motion had been communicated to them.
When the stone was projected to a sufficient height to perform somewhat
more than a quarter of a revolution in the air, it pitched down on its
edge, and fell with its lower side uppermost.
_Effects of earthquakes on the excavations of valleys._--The next class
of effects to be considered, are those more immediately connected with
the formation of valleys, in which the action of water was often
combined with that of the earthquake. The country agitated was composed,
as before stated, chiefly of argillaceous strata, intersected by deep
narrow valleys, sometimes from 500 to 600 feet deep. As the boundary
cliffs were in great part vertical, it will readily be conceived that,
amidst the various movements of the earth, the precipices overhanging
rivers, being without support on one side, were often thrown down. We
find, indeed, that inundations produced by obstructions in river-courses
are among the most disastrous consequences of great earthquakes in all
parts of the world, for the alluvial plains in the bottoms of valleys
are usually the most fertile and well-peopled parts of the whole
country; and whether the site of a town is above or below a temporary
barrier in the channel of a river, it is exposed to injury by the waters
either of a lake or flood.
_Landslips._--From each side of the deep valley or ravine of Terranuova
enormous masses of the adjoining flat country were detached, and cast
down into the course of the river, so as to give rise to great lakes.
Oaks, olive-trees, vineyards, and corn, were often seen growing at the
bottom of the ravine, as little injured as their former companions,
which still continued to flourish in the plain above, at least 500 feet
higher, and at the distance of about three-quarters of a mile. In one
part of this ravine was an enormous mass, 200 feet high and about 400
feet at its base, which had been detached by some former earthquake. It
is well attested, that this mass travelled down the ravine nearly four
miles, having been put in motion by the earthquake of the 5th of
February. Hamilton, after examining the spot, declared that this
phenomenon might be accounted for by the declivity of the valley, the
great abundance of rain which fell, and the great weight of the alluvial
matter which pressed behind it. Dolomieu also alludes to the fresh
impulse derived from other masses falling, and pressing upon the rear of
those first set in motion.
The first account sent to Naples of the two great slides or landslips
above alluded to, which caused a great lake near Terranuova, was couched
in these words:--"Two mountains on the opposite sides of a valley walked
from their original position until they met in the middle of the plain,
and there joining together, they intercepted the course of a river," &c.
The expressions here used resemble singularly those applied to
phenomena, probably very analogous, which are said to have occurred at
Fez, during the great Lisbon earthquake, as also in Jamaica and Java at
other periods.
Not far from Soriano, which was levelled to the ground by the great
shock of February, a small valley, containing a beautiful olive-grove,
called Fra Ramondo, underwent a most extraordinary revolution.
Innumerable fissures first traversed the river-plain in all directions,
and absorbed the water until the argillaceous substratum became soaked,
so that a great part of it was reduced to a state of fluid paste.
Strange alterations in the outline of the ground were the consequence,
as the soil to a great depth was easily moulded into any form. In
addition to this change, the ruins of the neighboring hills were
precipitated into the hollow; and while many olives were uprooted,
others remained growing on the fallen masses, and inclined at various
angles (see fig. 84). The small river Caridi was entirely concealed for
many days; and when at length it reappeared, it had shaped for itself an
entirely new channel.
_Buildings transported entire to great distances._--Near Seminara an
extensive olive-ground and orchard were hurled to a distance of two
hundred feet, into a valley sixty feet in depth. At the same time a deep
chasm was riven in another part of the high platform from which the
orchard had been detached, and the river immediately entered the
fissure, leaving its former bed completely dry. A small inhabited house,
standing on the mass of earth carried down into the valley, went along
with it entire, and without injury to the inhabitants. The olive-trees,
also, continued to grow on the land which had slid into the valley, and
bore the same year an abundant crop of fruit.
[Illustration: Fig. 84.
Changes of the surface at Fra Ramondo, near Soriano, in Calabria.
1, Portion of a hill covered with olives thrown down.
2, New bed of the river Caridi. 3, Town of Soriano.
]
Two tracts of land on which a great part of the town of Polistena stood,
consisting of some hundreds of houses, were detached into a contiguous
ravine, and nearly across it, about half a mile from their original
site; and what is most extraordinary, several of the inhabitants were
dug out from the ruins alive and unhurt.
Two tenements, near Mileto, called the Macini and Vaticano, occupying an
extent of ground about a mile long and half a mile broad, were carried
for a mile down a valley. A thatched cottage, together with large olive
and mulberry trees, most of which remained erect, were carried uninjured
to this extraordinary distance. According to Hamilton, the surface
removed had been long undermined by rivulets, which were afterwards in
full view on the bare spot deserted by the tenements. The earthquake
seems to have opened a passage in the adjoining argillaceous hills,
which admitted water charged with loose soil into the subterranean
channels of the rivulets immediately under the tenements, so that the
foundations of the ground set in motion by the earthquake were loosened.
Another example of subsidence, where the edifices were not destroyed,
is mentioned by Grimaldi, as having taken place in the city of
Catanzaro, the capital of the province of that name. The houses in the
quarter called San Giuseppe subsided with the ground to various depths
from two to four feet, but the buildings remained uninjured.
[Illustration: Fig. 85.
Landslips near Cinquefrondi, caused by the earthquake of 1783.]
It would be tedious, and our space would not permit us, to follow the
different authors through their local details of landslips produced in
minor valleys; but they are highly interesting, as showing to how great
an extent the power of rivers to widen valleys, and to carry away large
portions of soil towards the sea, is increased where earthquakes are of
periodical occurrence. Among other territories, that of Cinquefrondi,
was greatly convulsed, various portions of soil being raised or sunk,
and innumerable fissures traversing the country in all directions (see
fig. 85). Along the flanks of a small valley in this district there
appears to have been an almost uninterrupted line of landslips.
_Currents of mud._--Near S. Lucido, among other places, the soil is
described as having been "dissolved," so that large torrents of mud
inundated all the low grounds, like lava. Just emerging from this mud,
the tops only of trees and of the ruins of farm-houses were seen. Two
miles from Laureana, the swampy soil in two ravines became filled with
calcareous matter, which oozed out from the ground immediately before
the first great shock. This mud, rapidly accumulating, began, ere long,
to roll onward, like a flood of lava, into the valley, where the two
streams uniting, moved forward with increased impetus from east to west.
It now presented a breadth of 225 feet by 15 in depth, and, before it
ceased to move, covered a surface equal in length to an Italian mile. In
its progress it overwhelmed a flock of thirty goats, and tore up by the
roots many olive and mulberry trees, which floated like ships upon its
surface. When this calcareous lava had ceased to move, it gradually
became dry and hard, during which process the mass was lowered seven
feet and a half. It contained fragments of earth of a ferruginous
color, and emitting a sulphureous smell.
_Fall of the sea-cliffs._--Along the sea-coast of the Straits of
Messina, near the celebrated rock of Scilla, the fall of huge masses
detached from the bold and lofty cliffs overwhelmed many villas and
gardens. At Gian Greco, a continuous line of cliff, for a mile in
length, was thrown down. Great agitation was frequently observed in the
bed of the sea during the shocks, and, on those parts of the coast where
the movement was most violent, all kinds of fish were taken in
abundance, and with unusual facility. Some rare species, as that called
Cicirelli, which usually lie buried in the sand, were taken on the
surface of the waters in great quantity. The sea is said to have boiled
up near Messina, and to have been agitated as if by a copious discharge
of vapors from its bottom.
_Shore near Scilla inundated._--The prince of Scilla had persuaded a
great part of his vassals to betake themselves to their fishing-boats
for safety, and he himself had gone on board. On the night of the 5th of
February, when some of the people were sleeping in the boats, and others
on a level plain slightly elevated above the sea, the earth rocked, and
suddenly a great mass was torn from the contiguous Mount Jaci, and
thrown down with a dreadful crash upon the plain. Immediately
afterwards, the sea, rising more than twenty feet above the level of
this low tract, rolled foaming over it, and swept away the multitude. It
then retreated, but soon rushed back again with greater violence,
bringing with it some of the people and animals it had carried away. At
the same time every boat was sunk or dashed against the beach, and some
of them were swept far inland. The aged prince, with 1430 of his people,
was destroyed.
_State of Stromboli and Etna during the shocks._--The inhabitants of
Pizzo remarked that on the 5th of February, 1783, when the first great
shock afflicted Calabria, the volcano of Stromboli, which is in full
view of that town, and at the distance of about fifty miles, smoked
less, and threw up a less quantity of inflamed matter than it had done
for some years previously. On the other hand, the great crater of Etna
is said to have given out a considerable quantity of vapor towards the
beginning, and Stromboli towards the close, of the commotions. But as no
eruption happened from either of these great vents during the whole
earthquake, the sources of the Calabrian convulsions, and of the
volcanic fires of Etna and Stromboli, appear to be very independent of
each other; unless, indeed, they have the same mutual relation as
Vesuvius and the volcanoes of the Phlegraean Fields and Ischia, a violent
disturbance in one district serving as a safety-valve to the other, and
both never being in full activity at once.
_Excavation of valleys._--It is impossible for the geologist to consider
attentively the effect of this single earthquake of 1783, and to look
forward to the alterations in the physical condition of the country to
which a continued series of such movements will hereafter give rise,
without perceiving that the formation of valleys by running water can
never be understood, if we consider the question independently of the
agency of earthquakes. It must not be imagined that rivers only begin to
act when a country is already elevated far above the level of the sea,
for their action must of necessity be most powerful while land is
_rising_ and _sinking_ by successive movements. Whether Calabria is now
undergoing any considerable change of relative level, in regard to the
sea, or is, upon the whole, nearly stationary, is a question which our
observations, confined almost entirely to the last half century, cannot
possibly enable us to determine. But we know that strata, containing
species of shells identical with those now living in the contiguous
parts of the Mediterranean, have been raised in that country, as they
have in Sicily, to the height of several thousand feet.
Now, those geologists who grant that the present course of Nature in the
inanimate world has continued the same since the existing species of
animals were in being, will not feel surprised that the Calabrian
streams and rivers have cut out of such comparatively modern strata a
great system of valleys, varying in depth from fifty to six hundred
feet, and often several miles wide, if they consider how numerous may
have been the shocks which accompanied the uplifting of those recent
marine strata to so prodigious a height. Some speculators, indeed, who
disregard the analogy of existing nature, and who are always ready to
assume that her forces were more energetic in by-gone ages, may dispense
with a long series of movements, and suppose that Calabria "rose like an
exhalation" from the deep, after the manner of Milton's Pandemonium. But
such an hypothesis would deprive them of that peculiar removing force
required to form a regular system of deep and wide valleys; for _time_,
which they are so unwilling to assume, is essential to the operation.
Time must be allowed in the intervals between distinct convulsions, for
running water to clear away the ruins caused by landslips, otherwise the
fallen masses will serve as buttresses, and prevent the succeeding
earthquake from exerting its full power. The sides of the valley must be
again cut away by the stream, and made to form precipices and
over-hanging cliffs, before the next shock can take effect in the same
manner.
Possibly the direction of the succeeding shock may not coincide with
that of the valley, a great extent of adjacent country being equally
shaken. Still it will usually happen that no permanent geographical
change will be produced except in valleys. In them alone will occur
landslips from the boundary cliffs, and these will frequently divert the
stream from its accustomed course, causing the original ravine to become
both wider and more tortuous in its direction.
If a single convulsion of extreme violence should agitate at once an
entire hydrographical basin, or if the shocks should follow each other
too rapidly, the previously existing valleys would be annihilated,
instead of being modified and enlarged. Every stream might in that case
be compelled to begin its operations anew, and to shape out new
channels, instead of continuing to deepen and widen those already
excavated. But if the subterranean movements have been intermittent, and
if sufficient periods have always intervened between the severer shocks
to allow the drainage of the country to be nearly restored to its
original state, then are both the kind and degree of force supplied by
which running water may hollow out valleys of any depth or size
consistent with the elevation above the sea which the districts drained
by them may have attained.
When we read of the drying up and desertion of the channels of rivers,
the accounts most frequently refer to their deflection into some other
part of the same alluvial plain, perhaps several miles distant. Under
certain circumstances a change of level may undoubtedly force the water
to flow over into some distinct hydrographical basin; but even then it
will fall immediately into some other system of valleys already formed.
We learn from history that, ever since the first Greek colonists settled
in Calabria, that region has been subject to devastation by earthquakes;
and, for the last century and a half, ten years have seldom elapsed
without a shock; but the severer convulsions have not only been
separated by intervals of twenty, fifty, or one hundred years, but have
not affected precisely the same points when they recurred. Thus the
earthquake of 1783, although confined within the same geographical
limits as that of 1638, and not very inferior in violence, visited,
according to Grimaldi, very different districts. The points where the
local intensity of the force is developed being thus perpetually varied,
more time is allowed for the removal of separate mountain masses thrown
into river-channels by each shock.
_Number of persons who perished during the earthquake._--The number of
persons who perished during the earthquake in the two Calabrias and
Sicily, is estimated by Hamilton at about forty thousand; and about
twenty thousand more died by epidemics, which were caused by
insufficient nourishment, exposure to the atmosphere, and malaria,
arising from the new stagnant lakes and pools.
By far the greater number were buried under the ruins of their houses;
but many were burnt to death in the conflagrations which almost
invariably followed the shocks. These fires raged the more violently in
some cities, such as Oppido, from the immense magazines of oil which
were consumed.
Many persons were engulfed in deep fissures, especially the peasants
when flying across the open country, and their skeletons may perhaps be
buried in the earth to this day, at the depth of several hundred feet.
When Dolomieu visited Messina after the shock of Feb. 5th, he describes
the city as still presenting, at least at a distance, an imperfect image
of its ancient splendor. Every house was injured, but the walls were
standing; the whole population had taken refuge in wooden huts in the
neighborhood, and all was solitude and silence in the streets: it seemed
as if the city had been desolated by the plague, and the impression made
upon his feelings was that of melancholy and sadness. "But when I passed
over to Calabria, and first beheld Polistena, the scene of horror almost
deprived me of my faculties; my mind was filled with mingled compassion
and terror; nothing had escaped; all was levelled with the dust; not a
single house or piece of wall remained; on all sides were heaps of stone
so destitute of form, that they gave no conception of there ever having
been a town on the spot. The stench of the dead bodies still rose from
the ruins. I conversed with many persons who had been buried for three,
four, and even for five days; I questioned them respecting their
sensations in so dreadful a situation, and they agreed that of all the
physical evils they endured, thirst was the most intolerable; and that
their mental agony was increased by the idea that they were abandoned by
their friends, who might have rendered them assistance."[672]
It is supposed that about a fourth part of the inhabitants of Polistena,
and of some other towns, were buried alive, and might have been saved
had there been no want of hands; but in so general a calamity, where
each was occupied with his own misfortunes or those of his family, aid
could rarely be obtained. Neither tears, nor supplications, nor promises
of high rewards were listened to. Many acts of self-devotion, prompted
by parental and conjugal tenderness, or by friendship, or the gratitude
of faithful servants, are recorded; but individual exertions were, for
the most part, ineffectual. It frequently happened, that persons in
search of those most dear to them could hear their moans,--could
recognize their voices--were certain of the exact spot where they lay
buried beneath their feet, yet could afford them no succor. The piled
mass resisted all their strength, and rendered their efforts of no
avail.
At Terranuova, four Augustin monks, who had taken refuge in a vaulted
sacristy, the arch of which continued to support an immense pile of
ruins, made their cries heard for the space of four days. One only of
the brethren of the whole convent was saved, and "of what avail was his
strength to remove the enormous weight of rubbish which had overwhelmed
his companions?" He heard their voices die away gradually; and when
afterwards their four corpses were disinterred, they were found clasped
in each other's arms. Affecting narratives are preserved of mothers
saved after the fifth, sixth, and even seventh day of their interment,
when their infants or children had perished with hunger.
It might have been imagined that the sight of sufferings such as these
would have been sufficient to awaken sentiments of humanity and pity in
the most savage breasts; but while some acts of heroism are related,
nothing could exceed the general atrocity of conduct displayed by the
Calabrian peasants: they abandoned the farms, and flocked in great
numbers into the towns--not to rescue their countrymen from a lingering
death, but to plunder. They dashed through the streets, fearless of
danger, amid tottering walls and clouds of dust, trampling beneath their
feet the bodies of the wounded and half-buried, and often stripping
them, while yet living, of their clothes.[673]
_Concluding remarks._--But to enter more fully into these details would
be foreign to the purpose of the present work, and several volumes
would be required to give the reader a just idea of the sufferings
which the inhabitants of many populous districts have undergone during
the earthquakes of the last 150 years. A bare mention of the loss of
life--as that fifty or a hundred thousand souls perished in one
catastrophe--conveys to the reader no idea of the extent of misery
inflicted: we must learn, from the narratives of eye-witnesses, the
various forms in which death was encountered, the numbers who escaped
with loss of limbs or serious bodily injuries, and the multitude who
were suddenly reduced to penury and want. It has been often remarked,
that the dread of earthquakes is strongest in the minds of those who
have experienced them most frequently; whereas, in the case of almost
every other danger, familiarity with peril renders men intrepid. The
reason is obvious--scarcely any part of the mischief apprehended in this
instance is imaginary; the first shock is often the most destructive;
and, as it may occur in the dead of the night, or if by day, without
giving the least warning of its approach, no forethought can guard
against it; and when the convulsion has begun, no skill, or courage, or
presence of mind, can point out the path of safety. During the
intervals, of uncertain duration, between the more fatal shocks, slight
tremors of the soil are not unfrequent; and as these sometimes precede
more violent convulsions, they become a source of anxiety and alarm. The
terror arising from this cause alone is of itself no inconsiderable
evil.
Although sentiments of pure religion are frequently awakened by these
awful visitations, yet we more commonly find that an habitual state of
fear, a sense of helplessness, and a belief in the futility of all human
exertions, prepare the minds of the vulgar for the influence of a
demoralizing superstition.
Where earthquakes are frequent, there can never be perfect security of
property under the best government; industry cannot be assured of
reaping the fruits of its labor; and the most daring acts of outrage may
occasionally be perpetrated with impunity, when the arm of the law is
paralyzed by the general consternation. It is hardly necessary to add,
that the progress of civilization and national wealth must be retarded
by convulsions which level cities to the ground, destroy harbors, render
roads impassable, and cause the most cultivated valley-plains to be
covered with lakes, or the ruins of adjoining hills.
Those geologists who imagine that, at remote periods ere man became a
sojourner on earth, the volcanic agency was more energetic than now,
should be careful to found their opinion on strict geological evidence,
and not permit themselves to be biased, as they have often been, by a
notion, that the disturbing force would probably be mitigated for the
sake of man.
I shall endeavor to point out in the sequel, that the 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, and the very existence and
perpetuation of dry land secured. 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 may 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 should
increase at the same time; for it has been justly said, that the greater
the circle of light, the greater the boundary of darkness by which it is
surrounded.[674]