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

by Robert Mallet

CHAPTER III.

EXAMINATION ROUND THE COAST AS TO PERMANENT CHANGES OF LEVEL.

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On my way southwards, I received an introduction from the Intendente of Salerno, to Signor Palmieri, an engineer of the Ponte e Stradi, whom I fell in with at Eboli. In conversation he stated his opinion that since the shock of December 16th, the sea level all round the west coast, has been lower, i.e., the land higher than before. He sustained this, by reference to a quay or wharf wall not very long since erected by himself at Amalfi on the shore of the Gulf of Salerno. The level of the sea at half

tide, he said, was always previously at $a$ (Fig. 118), or coincident with the top of the timber work, at the toe of the sea wall, but then stood about one palm, or 10.38 inches English, below it at $b$. I examined into this on my return northwards, but the account of my observations will be best given here. On the 27th of February, 1858, at the lowest point of low water, of the afternoon tide at Amalfi, I found the sea-level to be 11 inches below the top of the cap sill or longitudinal timber, over the tops of the piling at the toe of the wharf wall, (which has a hollow parabolic curved sectional contour); that is to say, about half an inch below the haft-tide level $b$, according to Palmieri. Some loose volcanic sand, was heaped up at the foot of the wall above the permanent gravel of the beach beneath. Within a few hundred yards, I was able to find a sheltered nook between some rocks, where I noted the usual rise of tide, by the weed marks, to be 17 to 18 inches, and that high spring tides rose occasionally about 4 inches more.

I recurred to this spot at high water of the same tide, and although having to use a lanthorn, and a little wind having sprung up, I was yet able to ascertain a rise of tide of 16 inches. Returning to the quay wall, I found the water there, too agitated for direct observation; but referred to my adjacent tide gauge, the quiescent level of high water would then have been, 5 inches above the top of the cap sill, or at $d$, and with an 18 inch tide, 7 inches above same; or at high springs, about 11 inches above same. So that, the haft-tide level is still in reality, just about the level of the top of the cap sill at $a$, as fixed by Signor Palmieri before the earthquake, and no change of level of the land has taken place at this point of the coast. His erroneous conclusion, must have arisen, I presume, from his having mistaken at the time of observation, the periods of high, and of low water.

I also examined the coast carefully to the eastward of Torre del Greco, and to where the railway branches off to Castellammare, and where some of the firm lava streams from Vesuvius, have run into the sea, and afford the best natural marks as to tidal level that the bay presents, but was unable to find any evidence of recent change of level of the land.

I also examined the quays and beach at Salerno, the mouth of the river Vicentino, which falls into the Gulf of Salerno, S.E. of Monte Corvino, and the beds of the rivers Tusciano and Salaris, in the great plain of Pæstum, with the same negative result.

At Pæstum, the proprietor of the soil, who is also the appointed guardian of the antiquities of the place, was at home at his "Casone." He was perfectly familiar with every feature of the shore line, from the ancient city down to Agropoli, and had recently passed along it, but had remarked no changes since December 16th, 1857 though quite alive to the question of rise and fall of the land.

I conclude, therefore, that there is no evidence whatever of any permanent change of level of the land in connection with this earthquake, upon the west coast from Pozzuoli to Agropoli, and it is not conceivable that there should be any, upon the Adriatic coast, where the shock was only perceptible.