Alexander Agassiz, who had been urging me to do a memoir on volcanoes, financed a trip to Vesuvius when it exploded and poured out lava in 1906. Ottajano northeast of Vesuvius was demolished by jets of gravel and stones; and Boscotrecase at the south was invaded by black streams of heavy, sprouting, bouldery slag. Here was a change of habit, from heaping up lavas for thirty-four years, to collapse, internal avalanching, and pure steam explosion accompanied by remnants of stirred lava flow.
Why thirty-four years? A third of a century? Three times the sunspot interval? The previous steamblast explosion of Vesuvius before 1906 had been in 1872. In the case of Mount Pelée and Soufrière the intervals since past explosions had been fifty-one years and ninety years. But it should be pointed out that the Carib volcanoes had two years of terrifying rumblings, odors, and quakes just before 1902. Groundwater exists in large volume under all three volcanoes. Soufrière, Pelée and Vesuvius all began the steamblasts with collapsing craters, that is, with internal lava going down into the bowels of the earth. The lava usually showed in Vesuvius, whereas at Pelée and Soufrière it merely made fumaroles, or gas vents. Man, a mere microbe, could make nothing of hot sulfurous cracks.
On April 25 the electric train slowly pushed us up as far as the observatory station, beyond which all was destroyed. Outside Naples the fields were covered with two inches of gray-green dust, and pines and palms were loaded with a two or three foot drift of sand. Near the observatory a heavy six-inch mantle of sand and dust buried the lava fields. The Vesuvian cone was covered with straight sand slides, whitish gray, which occasionally slipped downward. The landscape was shrouded in drifts of white ashes revealing obscurely the slaggy contortions of lava beneath. Pure white steam boiled up from the cavity in the peak, surrounded by an older rain cloud, like a hat on the volcano’s crown.
My companions—Dr. Tempest Anderson and Messrs. Yeld and Brigg—were all from Yorkshire. We started the ascent of the twenty-nine degree slope in a strong west wind. The steam settled down on the summit, than alternated with clear spells. We followed the west profile of the cone straight up, noting how the funicular rails were twisted by landslides. Everything was covered with pebbles, sand, and dust, with here and there large fragments up to five feet across. We found solid footing on the radial elevations of either scoured old lava or packed fragments. The gullies were filled with deep sand.
The rim we could see ahead was the edge of the crater itself. The abruptness of the fall off, when we finally came to it, was startling in the extreme. The wind was pelting our necks with stinging sand grains which, incidentally, were ruinous to my new Kodak. Only occasionally did sunshine sift through the mixture of sand, steam, and cloud. We could make out an inward slope of thirty-five degrees, terminated 100 feet below by a jutting, fuming precipice. The circular curvature of the crater was embayed. The only noise was the howling wind. We could not see the opposite side of the collapsed cauldron a half mile across. The summit was 4,000 feet above sea level by aneroid measure, 350 feet lower than before the eruption. There was a great notch northeast toward Ottajano where thousands of tons of gravel were hurled clear over the top of Monte Somma, the encircling old ridge. The east-west diameter was left much greater than that of the north-south. The radial ridges and gullies were like a corrugated roof, and sand made a flattened angle of scree at the base of the scoured cone. The corrugations were not rain erosion, but were made by backfallen debris sliding. I got some photographs and Mr. Perret gave me others.
The big thing was the line of mountain blocks of earth crust. In Italy it is made up of Ischia, Pozzuoli, Vesuvius, Lipari, and Etna, whereas the Carribbee line is made up of Mount Misery, Montserrat, Guadeloupe, Dominica, Martinique, and St. Vincent. Such a line of broken earth blocks is a volcanic system. Hundreds of miles long, it is never quiet. A single place seems quiet because superficially we are totally unconscious of the other places. A microbe on the scalp knows nothing of the skin of the toes. Men are mere microbes on the skin of shore, sea, and island. And they are remote from any consciousness of sea bottom.
Vast distances and long intervals are writing records, but man does not measure them. He measures civilization, wars, and dynasties, not the adventures of the ground he dwells upon. Ground he considers static. Actually it is intensely dynamic. Occasionally it explodes and man is destroyed. Earth history and volcanic systems make wars look very small.
The tremendous accumulations of broken rocks over lava beds on the cone of Vesuvius, and on all the Caribbee Islands, recall the breccias, or volcanic conglomerates, of the Yellowstone and of the High Plateaus of Utah. Floods of basalt alternate with vast falls or outwashes of volcanic gravel. Avalanches, landslides, torrents, floods—call them what you will—cover immense areas of the Cordillera. Vesuvius and Pelée pile up cones, but the Caribbees and Italy are also heaped with agglomerates. Erosion destroys cones, but erosion makes agglomerations or valley fills of rocks and mud. This is the history of every volcanic system on the globe. Stübel discovered smooth basalt domes like Mauna Loa under every volcanic system.
In 1904 Vesuvius had vented a lava flow which stopped in September, and its cone was sharp, with only a little crater and inner conelet on top. In 1905 lava had flowed from a northwest split. On April 4, 1906, a splendid black cauliflower cloud arose. The northwest flow stopped and a southern radial rift made lava mouths progress 500, 1,800, and 2,400 feet below the top, more than halfway down the mountain. From the lower mouth came glassy pahoehoe, or smooth destructive streams intensely incandescent and liquid, quickly cooling to aa, or sprouting rough fudge, black crusts, and clinker. The molten porridge flowed as a snaky avalanche into the masonry village of Boscotrecase.
On April 7, at the crater, a column of boulder-laden steam shot up four miles, snapping with lightning. New lava mouths sent forking snakes crushing and swallowing parts of the village. A graveyard was neatly filled within its masonry wall, showing that internally the rocky torrent was a liquid.