Lava
2 of the 6 encyclopedias on this shelf carry an entry for Lava. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
la'va, the molten material poured out of volcanoes. As volcanoes are widely distributed, the lava poured out by them represents different parts of the interior of the earth and varies accordingly. When lava cools slowly it forms crystalline rocks; when it cools quickly it forms a glassy rock, of which obsidium is the best type. Characteristic rocks are basalt and porphyry, tufa and pumice. Disintegrating volcanic rock forms a fertile soil. The fertility of the slopes of the European volcanoes, as Vesuvius and Etna, tempts villagers within the zone of danger. In 1812 a volcanic eruption of St. Vincent covered the Barbadoes Islands with several inches, not of snow, but of fertile, fluffy black dust. The rich sugar-cane fields of Hawaii are of volcanic formation. During what is known as the tertiary geologic age a vast outflow of lava flooded the Pacific coast from Idaho to the ocean. It covered southern Idaho, the greater portion of Washington, eastern Oregon, and northeastern California. In cooling, it formed basaltic rock. The plains of the Snake and the Columbia are volcanic. Extensive areas near Flagstaff, Arizona, are covered with coarse black soil resembling crushed coke. Lava soil of high fertility covers large areas in Java, Japan, Italy, Sicily, and Hungary. Wherever rainfall is sufficient or water can be had, the valleys are exceedingly fertile. Some say that basaltic soil forms the best wheat land known. See Volcanoes; Soil ; Basalt ; Fingal'S Cave
Collier's New Encyclopedia (1921)
a term used vaguely of all in streams from volcanic vents, but more molten matter existing within or flowing specifically confined to the latter, the former being called trap. The lower part of it which has consolidated slowly and under pressure, tends to be of stony consistency, while the upper is scoriation. Some are trachytic, as in the Peak ceous. Lavas vary greatly in composi- Vesuvius and Auvergne; others andesitic, of Teneriffe; many are basaltic, as in the most modern in Vesuvius consist of as in the volcanoes of Chile. Some of green augite, and many of those of Etna of augite and Labrador felspar. partment of Mayenne, and one of the
What Has Changed in the Last Century
Both accounts describe lava well as chemistry and rock type — Collier's list of basaltic, andesitic and trachytic lavas, with their augite and labradorite feldspar, would still pass muster, and 'obsidium' is simply obsidian. What neither could supply is the reason volcanoes sit where they do: Aiton's guess that scattered volcanoes tap "different parts of the interior of the earth" gave way, after plate tectonics was accepted in the 1960s, to an account in which most lava is generated by partial melting of the mantle beneath spreading ridges, subduction zones and hotspots. The "vast outflow of lava" Aiton assigns to the Tertiary is now the Columbia River Basalt Group, dated to roughly 17–6 million years ago and linked to the same deep source that now lies under Yellowstone. The St Vincent volcano that dusted Barbados in 1812 has since erupted in 1902, 1979 and again in April 2021, and lava flows are now watched by satellite thermal sensors and gas spectrometers rather than from the slopes.
Written for this edition, 2026.