. The building of an island : being a sketch of the geological structure of the Danish West Indian island of St. Croix, or Santa Cruz. Geology -- Virgin Islands of the United States Saint Croix. 84 THE BUILDING OF AN ISLAND. known by the expressive name of "The ; The diagram (Fig. 29) shows an outline of it as seen from the north. v / V> %â M-. ^ca. <dO. In some cases the conditions during a volcanic eruption are such as to permit of a spectator remaining on, or even within, the edge of a crater during the eruption. In this respect Stromboli, in the Lipari Islands, which
. The building of an island : being a sketch of the geological structure of the Danish West Indian island of St. Croix, or Santa Cruz. Geology -- Virgin Islands of the United States Saint Croix. 84 THE BUILDING OF AN ISLAND. known by the expressive name of "The ; The diagram (Fig. 29) shows an outline of it as seen from the north. v / V> %â M-. ^ca. <dO. In some cases the conditions during a volcanic eruption are such as to permit of a spectator remaining on, or even within, the edge of a crater during the eruption. In this respect Stromboli, in the Lipari Islands, which has re- cently (May, 1907,) astonished the world by its activity, has hitherto presented a specially favorable field of study, because, although nearly always active, its activity has usually been of so moderate a character that the explosions which take place at short intervals at the bottom of the crater could be watched with very little danger to the onlooker. In this way it has been found that when an explosion is about to take place, there rises on the surface of the molten rock at the bottom of the crater a large bubble, which explodes, emitting a cloud of steam and of dust formed by some of the matter being blown into minute fragments. The explosion reveals the glowing molten mass below, and this lights up the column of steam and dust that has been thrown out from the vent, and thus gives rise to the popular but mistaken notion that flames issue from the crater; The dust produced by the explosion is known as volcanic ash, a name to which there can be no objection so long as we remember that there has been no combustion of any solid substance and that therefore the volcanic dust cannot be ash in the usual sense of the term. Where does the steam which causes the explosions come from ? Formerly it was supposed to be from the surface water of the earth, which was thought to have reached the hot rock through cracks, but it is now generallv believed that it comes from the roc
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