Volcanoes: What They are and What They Teach

by John W. Judd

A little to the west of the town of Puzzuoli on the Bay of Naples there stands a conical hill rising to the height of 440 feet above the level of the Mediterranean, and covering an area more than half a mile in diameter. Now we have the most conclusive evidence that in ancient times no such hill existed on this site, which was partly occupied by the Lucrine Lake, and the fact is recognised in the name which the hill bears, that of Monte Nuovo, or the 'New Mountain.' See [fig. 10].

Sir William Hamilton rendered admirable service to science by collecting all the contemporary records relating to this interesting case, and he was able to prove, by the testimony of several intelligent and trustworthy witnesses, that during the week following the 29th of September, 1538, this hill had gradually been formed of materials ejected from a volcanic vent which had opened upon this site.

Fig. 10. Monte Nuovo (440 ft. high) on the shores of the Bay of Naples.

HISTORY OF THE FORMATION OF MONTE NUOVO.

The records collected by Hamilton with others which have been discovered since his death prove most conclusively the following facts. During more than two years, the country round was affected by earthquakes, which gradually increased in intensity and attained their climax in the month of September 1538; on the 27th and 28th of that month these earthquake shocks are said to have been felt almost continuously day and night. About 8 o'clock on the morning of the 29th, a depression of the ground was noticed on the site of the future hill, and from this depression, water, which was at first cold and afterwards tepid, began to issue. Four hours afterwards the ground was seen to swell up and open, forming a gaping fissure, within which incandescent matter was visible. From this fissure numerous masses of stone, some of them 'as large as an ox,' with vast quantities of pumice and mud, were thrown: up to a great height, and these falling upon the sides of the vent formed a great mound. This violent ejection of materials continued for two days and nights, and on the third day a very considerable hill was seen to have been built up by the falling fragments, and this hill was climbed by some of the eye-witnesses of the eruption. The next day the ejections were resumed, and many persons who had ventured on the hill were injured, and several killed by the falling stones. The later ejections were however of less violence than the earlier ones, and seem to have died out on the seventh or eighth day after the beginning of the outburst. The great mass of this considerable hill would appear, according to the accounts which have been preserved, to have been built up by the materials which were ejected during two days and nights.

Monte Nuovo is a hill of truncated conical form, which rises to the height of 440 feet above the waters of the Mediterranean, and is now covered with thickets of stone-pine. The hill is entirely made up of volcanic scoriæ, lapilli, and dust, and the sloping sides have evidently been produced by these fragmentary materials sliding over one another till they attained the angle of rest; just as happens with the earth and stones tipped from railway-waggons during the construction of an embankment. In the centre of this conical hill is a vast circular depression, with steeply sloping sides, which is of such depth that its bottom is but little above the sea-level. This cup-shaped depression is the 'crater' of the volcano, and it has evidently been formed by the explosive action which has thrown out the materials immediately above the vent, and caused them to be accumulated around it.

Fig. 11.—Map of the district around Naples, showing Monte Nuovo and the surrounding volcanoes of older date.

The district lying to the west of Naples, in which the Monte Nuovo is situated, contains a great number of hills, all of which present a most striking similarity to that volcano. All these hills are truncated cones, with larger or smaller circular depressions at their summits, and they axe entirely composed of volcanic scoriæ, lapilli, and dust. Some of these hills are of considerably larger dimensions than the Monte Nuovo, while others are of smaller size, as shown in the annexed map, [fig. 11]. No stranger visiting the district, without previous information upon the subject, would ever suspect the fact that, while all the other hills of the district have existed from time immemorial, and are constantly mentioned in the works of Greek and Roman writers, this particular hill of Monte Nuovo came into existence less than 350 years ago.