At Stromboli we learn the lesson that the explosive force in volcanoes is that of steam.  The lava in the pipe is permeated with it much as is a thick boiling porridge.  The steam in boiling porridge is unable to escape freely and gathers into bubbles which in breaking spurt out drops of the pasty substance; in the same way the explosion of great bubbles of steam in the viscid lava shoots clots and fragments of it into the air.

Krakatoa.  The most violent eruption of history, that of Krakatoa, a small volcanic island in the strait between Sumatra and Java, occurred in the last week of August, 1883.  Continuous explosions shot a column of steam and ashes. seventeen miles in air.  A black cloud, beneath which was midnight darkness and from which fell a rain of ashes and stones, overspread the surrounding region to a distance of one hundred and fifty miles.  Launched on the currents of the upper air, the dust was swiftly carried westward to long distances.  Three days after the eruption it fell on the deck of a ship sixteen hundred miles away, and in thirteen days the finest impalpable powder from the volcano had floated round the globe.  For many months the dust hung over Europe and America as a faint lofty haze illuminated at sunrise and sunset with brilliant crimson.  In countries nearer the eruption, as in India and Africa, the haze for some time was so thick that it colored sun and moon with blue, green, and copper-red tints and encircled them with coronas.

At a distance of even a thousand miles the detonations of the eruption sounded like the booming of heavy guns a few miles away.  In one direction they were audible for a distance as great as that from San Francisco to Cleveland.  The entire atmosphere was thrown into undulations under which all barometers rose and fell as the air waves thrice encircled the earth.  The shock of the explosions raised sea waves which swept round the adjacent shores at a height of more than fifty feet, and which were perceptible halfway around the globe.

At the close of the eruption it was found that half the mountain had been blown away, and that where the central part of the island had been the sea was a thousand feet deep.

Martinique and st. Vincent.  In 1902 two dormant volcanoes of the West Indies, Mt.  Pelee in Martinique and Soufriere in St. Vincent, broke into eruption simultaneously.  No lava was emitted, but there were blown into the air great quantities of ashes, which mantled the adjacent parts of the islands with a pall as of gray snow.  In early stages of the eruption lakes which occupied old craters were discharged and swept down the ash-covered mountain valleys in torrents of boiling mud.