The Story Book of Science  by Jean Henri Fabre


"I T is not late yet, Uncle," said Jules; "you ought to tell us about those terrible mountains, those volcanoes that the showers of ashes come from."

At the word "volcano," Emile, who was already asleep, rubbed his eyes and became all attention. He too wanted to hear the great story. As usual, their uncle yielded to their entreaties.

"A volcano is a mountain that throws up smoke, calcined dust, red-hot stones, and melted matter called lava. The summit is hollowed out in a great excavation having the shape of a funnel, sometimes several leagues in circumference. That is what we call the crater. The bottom of the crater communicates with a tortuous conduit or chimney too deep to estimate. The principal volcanoes of Europe are: Vesuvius, near Naples; Etna in Sicily; Hecla in Iceland. Most of the time a volcano is either in repose or throwing up a simple plume of smoke; but from time to time, with intervals that may be very long, the mountain grumbles, trembles, and vomits torrents of fiery substances. It is then said to be in eruption. To give you a general idea of the most remarkable phenomena attending volcanic eruption, I will choose Vesuvius, the best known of the European volcanoes.

"An eruption is generally announced beforehand by a column of smoke that fills the orifice of the crater and rises vertically, when the air is calm, to nearly a mile in height. At this elevation it spreads out in a sort of blanket that intercepts the sun's rays. Some days before the eruption the column of smoke sinks down on the volcano, covering it with a big black cloud. Then the earth begins to tremble around Vesuvius; rumbling detonations under the ground are heard, louder and louder each moment, soon exceeding in intensity the most violent claps of thunder. You would think you heard the cannonades of a numerous artillery detonating ceaselessly in the mountain's sides.

"All at once a sheaf of fire bursts from the crater to the height of 2000 or 3000 meters. The cloud that is floating over the volcano is illumined by the redness of the fire; the sky seems inflamed. Millions of sparks dart out like lightning to the top of the blazing sheaf, describe great arcs, leaving on their way dazzling trails, and fall in a shower of fire on the slopes of the volcano. These sparks, so small from a distance, are incandescent masses of stone, sometimes several meters in dimension, and of a sufficient momentum to crush the most solid buildings in their fall. What hand-made machine could throw such masses of rock to such heights? What all our efforts united could not do even once, the volcano does over and over again, as if in play. For whole weeks and months these red blocks are thrown up by Vesuvius, in numbers like the sparks of a display of fireworks."

"It is both terrible and beautiful," said Jules. "Oh! how I should like to see an eruption, but far off, of course."

"And the people who are on the mountain?" questioned Emile.

"'They are careful not to go on the mountain at that time; they might lose their lives, suffocated by the smoke or crushed by the shower of red-hot stones.

"Meantime, from the depths of the mountain, through the volcanic chimney, ascends a flux of melted mineral substance, or lava, which pours out into the crater and forms a lake of fire as dazzling as the sun. Spectators who, from the plain, anxiously follow the progress of the eruption, are warned of the coming of the lava-flood by the brilliant illumination it throws on the volumes of smoke floating in the upper air. But the crater is full; then the ground suddenly shakes, bursts open with a noise of thunder, and through the crevasses as well as over the edges of the crater the lava flows in streams. The fiery current, formed of dazzling and paste-like matter similar to melted metal, advances slowly; the front of the lava-stream resembles a moving rampart on fire. One can flee before it, but everything stationary is lost. Trees blaze a moment on contact with the lava and sink down, reduced to charcoal; the thickest walls are calcined and fall over; the hardest rocks are vitrified, melted.

"The flow of lava comes to an end, sooner or later. Then subterranean vapors, freed from the enormous pressure of the fluid mass, escape with more violence than ever, carrying with them whirlwinds of fine dust that floats in sinister clouds and sinks down on the neighboring plain, or is even carried by the winds to a distance of hundreds of leagues. Finally, the terrible mountain calms down, and peace is restored for an indefinite time."

"If there are towns near the volcanoes, cannot those streams of fire reach them? Cannot those clouds of ashes bury them?" asked Jules.

"Unfortunately all that is possible and has happened. I will tell you about it to-morrow, for it is time to go to bed now."