Great Neapolitan Earthquake of 1857/Part II. Ch. XX

by Robert Mallet

Chapter XX.

Sarconi to Saponara.

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I left Sarconi, where little could be learned, and pushed on by the valley of the Moglia, through about two miles of fine oak forest for Saponara.

Having recrossed the Sciavra, I paused upon the S. E. slope of a low hill, south of Saponara, and within half a mile of what was a few weeks since, a town of six thousand inhabitants, now a shapeless heap of ruin.

To the west, on the recent ruins of a Capuchin convent, under Il Monte, and to the east, on the opposite bank of the Sciavra, on the piano, in the fork between it and the Agri, are the ruins of the ancient Roman city of Grumentum.

The low hill, on which I am, like all those hereabouts, is of ill-compacted limestone, in beds nearly horizontal, dipping here 10° W., and much covered with deep alluvium. These must be reposing perfectly unconformably, against the limestone beds, of which the lofty and steep conoidal hill upon which Saponara stood, is composed.

These run through the mass of this hill, tilted to within 15° of vertical, and in a direction, generally, of a few degrees to the west of north and south.

The hill itself is nearly conoidal, rather narrower in its N. E. and S. W. diameter, than at right angles thereto: it is extremely steep, and rises from 900 to 1000 feet (by the eye) above the river Agri.

The town covered the summit, and spread some way down the flanks all round, descending most, upon the east side. The ancient Norman Castello Cilliberti, crowned the crest, which was bare limestone rock, and equally bare for 200 or 300 feet downwards. Beds of increasing thickness of alluvium then begin to cover it, and as it slopes down rapidly at an angle of nearly 45° to the Agri, these become 70 to 100 feet thick.

The opposite bank of the river, running N. W. to S. E., which I can see about 400 feet below me, consists of still deeper alluvium, forming part of the Piano Spineto, &c., resting upon horizontal and exposed beds of clays and schaly argillaceous rocks.

To the north and N. W., beyond the hill of Saponara, the Piano of Mattine delle Rose, extends for some five or six miles, all of such formations, and beyond that the mountains rise to Marsico Vetico, and beyond to the crest of Monte Voltorino. It was from this direction that the blow reached Saponara—delivered end on through its vertical beds, from the vast mass of loose material of the piano. Insulated to a depth of 1000 feet, the Agri and Sciavra running round its base from N. W. to south, peaked, narrow, and abrupt, and surrounded by horizontally abutting, dense and inelastic formations, the summit of the hill and the unhappy town upon it, must have shook and swayed like a mast, after the shock of the 16th of December.

The appearance of the ruin of Saponara was appalling. As I advanced, and gradually ascended close to it upon the S. E., and looking north, literally nothing remained standing, upon the crest, but the Castello Cilliberti (Photog. No. 251). Its roofs and floors were fallen in, its towers split or fallen, and many of its massive, indurated, ancient, and buttressed walls prostrated. All the upper part of the town, that which had been the most thickly built upon and densely inhabited, was now strewed around in featureless ruin; acres of ground were covered and heaped, with rounded mounds and sloping avalanches of white and dusty debris, but not a wall, or even the base of one, standing or visible.

Upon the very summit (to the right of the Castello Cilliberti, Photog. No. 251) may be seen projecting above the mass of rubbish the solitary fragment remaining erect of the ancient church,—a building of enormous solidity, massive, and ancient—and whose masonry, indurated by time, attested, by the enormous blocks in which some of its quoins were dislodged, its resistance to the terrible violence of the shock here. These are seen from a closer point of view in Photog. No. 252, looking nearly northward.

It was not, however, until having passed beneath the town, to the north of it, and looked back upon it, that the awful character of its desolation became fully developed.

Seen from this side (Photog. No. 253) the summit and far down the slope all round, presented nothing but a rounded knoll—shadowless and pale—of chalky stone and rubbish, without line or trace of street or house remaining; it might have seemed an abandoned stone quarry, or the rubbish of a chalk pit, save that its rounded and monotonous outline, was broken here and there by beams and blackened timbers that rooted in the rubbish stood thrown up in wild confusion against the sky like the gaunt arms of despair.^[1] Such an horizon high above me, and close around, on all sides the cold and dripping huts, thrown together, of whatever ruin had first presented to the hand, and filled with wounded and perishing beings, depressed the spirits of even the passing observer, to an extent that made me readily comprehend, the dull and stupefied patience, with which the survivors still cowered round the ruin of their homes.

There was less of the town upon the north, than upon the south slope of the hill; and as the blow came from the N. W., the “free lying stratum” was at the south and S. E. side, so that the condition for destruction, and the extent of food for it, were both here the greatest possible.

The only portion in which walls were standing at all, and still showing something of the features of a town, though shattered and in great part roofless, was at the east side, a long way down from the summit, as seen in part in Photog. No. 251, and in Photog. No. 254 (Col. Roy. Soc.), from the east side, looking back westward and northward.

No more complete proof could have been afforded of the fact, that the utter destruction of the town was due to the swaying of the hill itself upon which it stood, and not to some great increase at this region, of the dimensions or velocity of the earth-wave itself, than the finding several buildings around the base of the hill, and upon the deep alluvium close to its junction with the limestone of which it is composed, comparatively safe—all, however, severely shattered. Of these an example occurs in a house of two stories, seen to the left and low down in Photog No. 253.

The Castello, and the portion of the town below it to the east, gave abundant measures, of direction and emergence. The wave-path was sub-abnormal to almost every building in the place, and vast wedge-shaped masses were thrown out everywhere, some of which may be seen in the Photographs.

The examination of the buildings of the Castello resulted in a wave-path 150° E. of north to south, and an emergence of 14° to 16° from the north.

The buildings on the east slope gave a rather different wave-path; the average of a great many giving 120° 30′ E. of north, and a less emergence 12° to 15° from the north.

I take the former, however, as the true wave-path here, and deem the difference lower down to arise from the gyratory oscillation of the hill itself. A further proof of this was, that on traversing round its base, I found that while all the buildings there situated, gave a prevalent direction of wave-path about the same as above, they also showed complicated secondary fissures in directions that indicated their production by oscillations, emanating everywhere radially from the centre of the hill. I conclude, therefore, that the first great blow which prostrated in a moment the town, came as above. The hill itself, set to oscillate in the same plane as that of the path of the wave, rapidly began to oscillate in other planes, in fact, became a conical pendulum, and hence whatever buildings remained standing but fissured, by the primary blow, were again fissured in new directions or prostrated by this proper motion of the mass of the hill.

There were even evidences in the Castello at top (where these secondary motions were, of course, a maximum) of portions that had been broken out and disjointed, in the direction of the original wave, and by it, having been thrown afterwards, in directions nearly orthogonal to it.

It was difficult to get any indication, from which to calculate velocity here, or any approximation to the amplitude of the wave, nearly everything being totally prostrate and the history of its fall, a blank; the bells, for example, of the church, were many feet deep under stone and rubbish.

The direction of the wave being generally sub-abnormal, rendered it difficult to find any walls at the Castello, directly across the plane of which, the force had passed, and so circumstanced, that, being found still standing, they would afford to calculation, a limit beyond which, the total velocity of the summit of the hill could not have reached. In fact, had the wave and first oscillation of the hill, together been normal or subnormal to the walls of the Castello, not one stone of it would have been left standing; its remnant owed its remaining erect, mainly to the diagonal direction of its walls in reference to the wave, as may be readily seen, in the case of the buttressed curtain wall to the left in Photog. No. 251.

I was enabled, however, to find one massive piece of wall at the north side, whose condition admitted of its being used as a tolerable measure of this limiting velocity. Its lengthway was 72° E. of north; it was therefore within 12° of being transverse to the path of the primary wave.

It was a curtain wall of old rubble masonry, connected with buildings or towers at both ends about 40 feet apart, but in advance of one, so that it had very slight bond with that tower; while at the other an old settlement, or crack, broke a good deal of the connection. This wall was cracked nearly horizontally, about a foot above its base, and leaned over to the north about 1 1/2 inch. It had no batter: its thickness was 2.75 feet, and its height 20 feet. We can calculate the horizontal velocity necessary to have fractured its base, without overthrowing it, from the equation―

$V={\tfrac {2}{3}}g\times {\frac {b\mathrm {L} }{a^{2}}}$

here b = 2.75 feet; and to allow for the wall being 12° out of square to the wave-path, we shall take it = 2.8 feet; a = 20 feet, L = 2 × 52 feet. The coefficient for rubble limestone masonry of this highly indurated mortar being fully double that of ordinary work. Then

$V=21.46\times {\frac {104\times 2.8}{400}}=15.623$ feet per second.

I have no measure of the value of e, for Saponars, except those of the Castello, the maximum of which was 16°. We may assume it about the same as at Sarconi,= 16° 25′; and taking the velocity of the wave itself (in its normal direction) to be the same as at Polla = 12.97 feet per second, we have its horizontal velocity = 12.97/sec e = 12.45 ft. per second; deducting which from the preceding, we obtain 3.173 feet per second as the velocity of oscillation of the hill of Saponara itself, which may be considered as having been horizontal in direction.

The extreme limit of total velocity then, at Saponara, cannot have exceeded about sixteen per second, only about three feet per second greater than at Polla, Padula, &c.—a striking proof how small an increment of velocity, is sufficient to sweep all before it.

1. These timbers had been removed for huts and fuel between the time of my visit and that of taking the photographs, February to May, 1857.