During historic times a considerable number of new volcanoes have been formed, both on land and in the bed of the sea, the latter resulting in the birth of new islands. Aside from certain newly formed volcanoes, the origin of which has been recorded by ancient writers of Greece, Rome, and Japan, a few more modern instances may be cited.
Near Pozzuoli is a hill called Monte Nuovo, 440 feet high, which is hardly distinguishable from the other low volcanic cones among which it stands, and which are mentioned by several classical writers. Monte Nuovo was formed by an eruption which broke out September 29, 1538, the ground swelling up and bursting, leaving a fissure, which disclosed glowing lava, and which ejected great masses of blocks, sand, and ash. The activity lasted for a week and has not since been repeated.
Fig. 17. - Monte Nuovo, near Pozzuoli, formed in 1538.
Jorullo, in Mexico, was formed in 1759, the eruptions continuing for several years and then dying out. Immense quantities oi lava flowed forth and several "cinder cones" were built up, one of which is 1300 feet high. Isalco, a volcano on the west coast of Central America, north of the city of San Salvador, was first formed in 1770, and has been in almost uninterrupted activity ever since, sometimes with great violence. A cone of more than 2000 feet in height has been built up. In 1831 a new island appeared off the southwest coast of Sicily, where previous soundings had shown a depth of 100 fathoms, and in the course of a few weeks grew to a height of 200 feet above the sea and a diameter of a mile at sea-level. The activity soon ceased and the island, composed of loose materials, was swept away by the sea.
Fig. 18. - Another view of the crater-floor and walls of Kilauea. (U. S. G. S).
In the Greek archipelago the group of islands known as Santorin has been the scene of repeated operations for more than 2000 years. The outer islands are evidently fragments of an old crater ring, within which are several small islands, which were formed in 186 B.C., 1573, 1707, and 1866, respectively.
Finally may be mentioned an especially interesting group of three new islands, the Bogoslofs, north of the line of the Aleutian islands, Alaska. The first of the islands, Old Bogoslof, was formed by a submarine eruption in 1796, which was observed by a Russian trader. New Bogoslof was formed in 1883 and was first seen in September of that year, but the exact date of origin is not known. A third and very large island, composed of jagged lava, was seen between the older ones on May 28, 1906, "giving off clouds of steam and smoke from any number of little craters scattered all over it." (C. H. Gilbert).