Volcano
Aiton's Encyclopedia (1910)
a mountain or hill from which lava, heated rock material, and gases are ejected. The term was applied first to Mount Etna, the supposed home of Vulcanus, the god of fire. The material ejected is apt to give a volcano the form of a cone. The opening is surrounded usually by a pit-shaped cavity called a crater. The crater of Mauna Loa in Hawaii is 13,000 feet wide and 800 feet deep. Frequently there are many additional small openings. Within ten miles of the main crater, Mount Etna has over two hundred small vents. Many volcanoes have been quiet so long that they are regarded as extinct. Many such cold, lofty peaks exist in the Sierra Nevada Mountains of California. Volcanoes not lately in a state of eruption but which are thought likely to be resting only are termed dormant. Volcanoes vary greatly in height. Some are scarcely above sea level. Vesuvius is 4,000 feet high. Cotopaxi in the Andes is the highest active volcano. It rises through the clouds to an altitude of 20,000 feet. There are over three hundred active volcanoes. They are widely distributed. A series encircles the Pacific Ocean; a second series runs east and west, including the volcanoes of the West Indies , the Canaries, the Azores, and the Mediterranean region. Where the Pacific circle crosses the east and west series volcanic activity is marked. The region of greatest volcanic activity is that of Java and adjacent islands. Latitude appears to have no influence. Erebus within the Antarctic Circle reddens the southern sky, and Mount Hecla in Iceland rivals Vesuvius in activity. Pompeii was overwhelmed by an eruption of Vesuvius in 79. Late in August, 1883, an eruption in an island in the Strait of Sunda created a cavity into which the sea rushed with violence, setting waves in motion that overwhelmed and drowned villages. The cause of eruption is not known with certainty but it is believed that internal heat forms gases that expand and drive out the molten material as exploding powder drives the bullet from a gun. See Lava ; Basalt ; Hecla ; Etna ; Vesuvius ; Pompeii ; Cotopaxi ; Stromboli ; Geysers
What Has Changed in the Last Century
When Aiton's wrote in 1910 that "the cause of eruption is not known with certainty," it was stating the honest limit of the science; the answer arrived in the 1960s with plate tectonics, which showed that the "Pacific circle" of volcanoes the entry describes marks subduction zones where wet oceanic crust sinks and triggers melting, while Hawaii sits over a stationary mantle hotspot. The count has grown too: the Smithsonian's Global Volcanism Program lists roughly 1,350 volcanoes with eruptions in the last 12,000 years, against the entry's "over three hundred active," with 40 to 50 erupting on any given day. Cotopaxi has lost its title, since Ojos del Salado in Chile, at about 22,600 feet, is now generally called the world's highest volcano. And the confidence about extinction has faded — California's Long Valley and Mono-Inyo systems are treated as live, Lassen Peak in the Cascades erupted from 1914 to 1917, and the Hunga Tonga blast of January 2022 sent a plume higher into the atmosphere than any eruption on instrumental record.
Written for this edition, 2026.